compiler/rustc_codegen_gcc/src/intrinsic/mod.rs

   1 pub mod llvm;
   2 mod simd;
   3
   4 use gccjit::{ComparisonOp, Function, RValue, ToRValue, Type, UnaryOp};
   5 use rustc_codegen_ssa::MemFlags;
   6 use rustc_codegen_ssa::base::wants_msvc_seh;
   7 use rustc_codegen_ssa::common::{IntPredicate, span_invalid_monomorphization_error};
   8 use rustc_codegen_ssa::mir::operand::{OperandRef, OperandValue};
   9 use rustc_codegen_ssa::mir::place::PlaceRef;
  10 use rustc_codegen_ssa::traits::{ArgAbiMethods, BaseTypeMethods, BuilderMethods, ConstMethods, IntrinsicCallMethods};
  11 use rustc_middle::bug;
  12 use rustc_middle::ty::{self, Instance, Ty};
  13 use rustc_middle::ty::layout::LayoutOf;
  14 use rustc_span::{Span, Symbol, symbol::kw, sym};
  15 use rustc_target::abi::HasDataLayout;
  16 use rustc_target::abi::call::{ArgAbi, FnAbi, PassMode};
  17 use rustc_target::spec::PanicStrategy;
  18
  19 use crate::abi::GccType;
  20 use crate::builder::Builder;
  21 use crate::common::{SignType, TypeReflection};
  22 use crate::context::CodegenCx;
  23 use crate::type_of::LayoutGccExt;
  24 use crate::intrinsic::simd::generic_simd_intrinsic;
  25
  26 fn get_simple_intrinsic<'gcc, 'tcx>(cx: &CodegenCx<'gcc, 'tcx>, name: Symbol) -> Option<Function<'gcc>> {
  27     let gcc_name = match name {
  28         sym::sqrtf32 => "sqrtf",
  29         sym::sqrtf64 => "sqrt",
  30         sym::powif32 => "__builtin_powif",
  31         sym::powif64 => "__builtin_powi",
  32         sym::sinf32 => "sinf",
  33         sym::sinf64 => "sin",
  34         sym::cosf32 => "cosf",
  35         sym::cosf64 => "cos",
  36         sym::powf32 => "powf",
  37         sym::powf64 => "pow",
  38         sym::expf32 => "expf",
  39         sym::expf64 => "exp",
  40         sym::exp2f32 => "exp2f",
  41         sym::exp2f64 => "exp2",
  42         sym::logf32 => "logf",
  43         sym::logf64 => "log",
  44         sym::log10f32 => "log10f",
  45         sym::log10f64 => "log10",
  46         sym::log2f32 => "log2f",
  47         sym::log2f64 => "log2",
  48         sym::fmaf32 => "fmaf",
  49         sym::fmaf64 => "fma",
  50         sym::fabsf32 => "fabsf",
  51         sym::fabsf64 => "fabs",
  52         sym::minnumf32 => "fminf",
  53         sym::minnumf64 => "fmin",
  54         sym::maxnumf32 => "fmaxf",
  55         sym::maxnumf64 => "fmax",
  56         sym::copysignf32 => "copysignf",
  57         sym::copysignf64 => "copysign",
  58         sym::floorf32 => "floorf",
  59         sym::floorf64 => "floor",
  60         sym::ceilf32 => "ceilf",
  61         sym::ceilf64 => "ceil",
  62         sym::truncf32 => "truncf",
  63         sym::truncf64 => "trunc",
  64         sym::rintf32 => "rintf",
  65         sym::rintf64 => "rint",
  66         sym::nearbyintf32 => "nearbyintf",
  67         sym::nearbyintf64 => "nearbyint",
  68         sym::roundf32 => "roundf",
  69         sym::roundf64 => "round",
  70         sym::abort => "abort",
  71         _ => return None,
  72     };
  73     Some(cx.context.get_builtin_function(&gcc_name))
  74 }
  75
  76 impl<'a, 'gcc, 'tcx> IntrinsicCallMethods<'tcx> for Builder<'a, 'gcc, 'tcx> {
  77     fn codegen_intrinsic_call(&mut self, instance: Instance<'tcx>, fn_abi: &FnAbi<'tcx, Ty<'tcx>>, args: &[OperandRef<'tcx, RValue<'gcc>>], llresult: RValue<'gcc>, span: Span) {
  78         let tcx = self.tcx;
  79         let callee_ty = instance.ty(tcx, ty::ParamEnv::reveal_all());
  80
  81         let (def_id, substs) = match *callee_ty.kind() {
  82             ty::FnDef(def_id, substs) => (def_id, substs),
  83             _ => bug!("expected fn item type, found {}", callee_ty),
  84         };
  85
  86         let sig = callee_ty.fn_sig(tcx);
  87         let sig = tcx.normalize_erasing_late_bound_regions(ty::ParamEnv::reveal_all(), sig);
  88         let arg_tys = sig.inputs();
  89         let ret_ty = sig.output();
  90         let name = tcx.item_name(def_id);
  91         let name_str = name.as_str();
  92
  93         let llret_ty = self.layout_of(ret_ty).gcc_type(self, true);
  94         let result = PlaceRef::new_sized(llresult, fn_abi.ret.layout);
  95
  96         let simple = get_simple_intrinsic(self, name);
  97         let llval =
  98             match name {
  99                 _ if simple.is_some() => {
 100                     // FIXME(antoyo): remove this cast when the API supports function.
 101                     let func = unsafe { std::mem::transmute(simple.expect("simple")) };
 102                     self.call(self.type_void(), func, &args.iter().map(|arg| arg.immediate()).collect::<Vec<_>>(), None)
 103                 },
 104                 sym::likely => {
 105                     self.expect(args[0].immediate(), true)
 106                 }
 107                 sym::unlikely => {
 108                     self.expect(args[0].immediate(), false)
 109                 }
 110                 kw::Try => {
 111                     try_intrinsic(
 112                         self,
 113                         args[0].immediate(),
 114                         args[1].immediate(),
 115                         args[2].immediate(),
 116                         llresult,
 117                     );
 118                     return;
 119                 }
 120                 sym::breakpoint => {
 121                     unimplemented!();
 122                 }
 123                 sym::va_copy => {
 124                     unimplemented!();
 125                 }
 126                 sym::va_arg => {
 127                     unimplemented!();
 128                 }
 129
 130                 sym::volatile_load | sym::unaligned_volatile_load => {
 131                     let tp_ty = substs.type_at(0);
 132                     let mut ptr = args[0].immediate();
 133                     if let PassMode::Cast(ty) = fn_abi.ret.mode {
 134                         ptr = self.pointercast(ptr, self.type_ptr_to(ty.gcc_type(self)));
 135                     }
 136                     let load = self.volatile_load(ptr.get_type(), ptr);
 137                     // TODO(antoyo): set alignment.
 138                     self.to_immediate(load, self.layout_of(tp_ty))
 139                 }
 140                 sym::volatile_store => {
 141                     let dst = args[0].deref(self.cx());
 142                     args[1].val.volatile_store(self, dst);
 143                     return;
 144                 }
 145                 sym::unaligned_volatile_store => {
 146                     let dst = args[0].deref(self.cx());
 147                     args[1].val.unaligned_volatile_store(self, dst);
 148                     return;
 149                 }
 150                 sym::prefetch_read_data
 151                     | sym::prefetch_write_data
 152                     | sym::prefetch_read_instruction
 153                     | sym::prefetch_write_instruction => {
 154                         unimplemented!();
 155                     }
 156                 sym::ctlz
 157                     | sym::ctlz_nonzero
 158                     | sym::cttz
 159                     | sym::cttz_nonzero
 160                     | sym::ctpop
 161                     | sym::bswap
 162                     | sym::bitreverse
 163                     | sym::rotate_left
 164                     | sym::rotate_right
 165                     | sym::saturating_add
 166                     | sym::saturating_sub => {
 167                         let ty = arg_tys[0];
 168                         match int_type_width_signed(ty, self) {
 169                             Some((width, signed)) => match name {
 170                                 sym::ctlz | sym::cttz => {
 171                                     let func = self.current_func.borrow().expect("func");
 172                                     let then_block = func.new_block("then");
 173                                     let else_block = func.new_block("else");
 174                                     let after_block = func.new_block("after");
 175
 176                                     let arg = args[0].immediate();
 177                                     let result = func.new_local(None, arg.get_type(), "zeros");
 178                                     let zero = self.cx.context.new_rvalue_zero(arg.get_type());
 179                                     let cond = self.cx.context.new_comparison(None, ComparisonOp::Equals, arg, zero);
 180                                     self.llbb().end_with_conditional(None, cond, then_block, else_block);
 181
 182                                     let zero_result = self.cx.context.new_rvalue_from_long(arg.get_type(), width as i64);
 183                                     then_block.add_assignment(None, result, zero_result);
 184                                     then_block.end_with_jump(None, after_block);
 185
 186                                     // NOTE: since jumps were added in a place
 187                                     // count_leading_zeroes() does not expect, the current blocks
 188                                     // in the state need to be updated.
 189                                     *self.current_block.borrow_mut() = Some(else_block);
 190                                     self.block = Some(else_block);
 191
 192                                     let zeros =
 193                                         match name {
 194                                             sym::ctlz => self.count_leading_zeroes(width, arg),
 195                                             sym::cttz => self.count_trailing_zeroes(width, arg),
 196                                             _ => unreachable!(),
 197                                         };
 198                                     else_block.add_assignment(None, result, zeros);
 199                                     else_block.end_with_jump(None, after_block);
 200
 201                                     // NOTE: since jumps were added in a place rustc does not
 202                                     // expect, the current blocks in the state need to be updated.
 203                                     *self.current_block.borrow_mut() = Some(after_block);
 204                                     self.block = Some(after_block);
 205
 206                                     result.to_rvalue()
 207                                 }
 208                                 sym::ctlz_nonzero => {
 209                                     self.count_leading_zeroes(width, args[0].immediate())
 210                                 },
 211                                 sym::cttz_nonzero => {
 212                                     self.count_trailing_zeroes(width, args[0].immediate())
 213                                 }
 214                                 sym::ctpop => self.pop_count(args[0].immediate()),
 215                                 sym::bswap => {
 216                                     if width == 8 {
 217                                         args[0].immediate() // byte swap a u8/i8 is just a no-op
 218                                     }
 219                                     else {
 220                                         // TODO(antoyo): check if it's faster to use string literals and a
 221                                         // match instead of format!.
 222                                         let bswap = self.cx.context.get_builtin_function(&format!("__builtin_bswap{}", width));
 223                                         let mut arg = args[0].immediate();
 224                                         // FIXME(antoyo): this cast should not be necessary. Remove
 225                                         // when having proper sized integer types.
 226                                         let param_type = bswap.get_param(0).to_rvalue().get_type();
 227                                         if param_type != arg.get_type() {
 228                                             arg = self.bitcast(arg, param_type);
 229                                         }
 230                                         self.cx.context.new_call(None, bswap, &[arg])
 231                                     }
 232                                 },
 233                                 sym::bitreverse => self.bit_reverse(width, args[0].immediate()),
 234                                 sym::rotate_left | sym::rotate_right => {
 235                                     // TODO(antoyo): implement using algorithm from:
 236                                     // https://blog.regehr.org/archives/1063
 237                                     // for other platforms.
 238                                     let is_left = name == sym::rotate_left;
 239                                     let val = args[0].immediate();
 240                                     let raw_shift = args[1].immediate();
 241                                     if is_left {
 242                                         self.rotate_left(val, raw_shift, width)
 243                                     }
 244                                     else {
 245                                         self.rotate_right(val, raw_shift, width)
 246                                     }
 247                                 },
 248                                 sym::saturating_add => {
 249                                     self.saturating_add(args[0].immediate(), args[1].immediate(), signed, width)
 250                                 },
 251                                 sym::saturating_sub => {
 252                                     self.saturating_sub(args[0].immediate(), args[1].immediate(), signed, width)
 253                                 },
 254                                 _ => bug!(),
 255                             },
 256                             None => {
 257                                 span_invalid_monomorphization_error(
 258                                     tcx.sess,
 259                                     span,
 260                                     &format!(
 261                                         "invalid monomorphization of `{}` intrinsic: \
 262                                       expected basic integer type, found `{}`",
 263                                       name, ty
 264                                     ),
 265                                 );
 266                                 return;
 267                             }
 268                         }
 269                     }
 270
 271                 sym::raw_eq => {
 272                     use rustc_target::abi::Abi::*;
 273                     let tp_ty = substs.type_at(0);
 274                     let layout = self.layout_of(tp_ty).layout;
 275                     let _use_integer_compare = match layout.abi() {
 276                         Scalar(_) | ScalarPair(_, _) => true,
 277                         Uninhabited | Vector { .. } => false,
 278                         Aggregate { .. } => {
 279                             // For rusty ABIs, small aggregates are actually passed
 280                             // as `RegKind::Integer` (see `FnAbi::adjust_for_abi`),
 281                             // so we re-use that same threshold here.
 282                             layout.size() <= self.data_layout().pointer_size * 2
 283                         }
 284                     };
 285
 286                     let a = args[0].immediate();
 287                     let b = args[1].immediate();
 288                     if layout.size().bytes() == 0 {
 289                         self.const_bool(true)
 290                     }
 291                     /*else if use_integer_compare {
 292                         let integer_ty = self.type_ix(layout.size.bits()); // FIXME(antoyo): LLVM creates an integer of 96 bits for [i32; 3], but gcc doesn't support this, so it creates an integer of 128 bits.
 293                         let ptr_ty = self.type_ptr_to(integer_ty);
 294                         let a_ptr = self.bitcast(a, ptr_ty);
 295                         let a_val = self.load(integer_ty, a_ptr, layout.align.abi);
 296                         let b_ptr = self.bitcast(b, ptr_ty);
 297                         let b_val = self.load(integer_ty, b_ptr, layout.align.abi);
 298                         self.icmp(IntPredicate::IntEQ, a_val, b_val)
 299                     }*/
 300                     else {
 301                         let void_ptr_type = self.context.new_type::<*const ()>();
 302                         let a_ptr = self.bitcast(a, void_ptr_type);
 303                         let b_ptr = self.bitcast(b, void_ptr_type);
 304                         let n = self.context.new_cast(None, self.const_usize(layout.size().bytes()), self.sizet_type);
 305                         let builtin = self.context.get_builtin_function("memcmp");
 306                         let cmp = self.context.new_call(None, builtin, &[a_ptr, b_ptr, n]);
 307                         self.icmp(IntPredicate::IntEQ, cmp, self.const_i32(0))
 308                     }
 309                 }
 310
 311                 sym::black_box => {
 312                     args[0].val.store(self, result);
 313
 314                     let block = self.llbb();
 315                     let extended_asm = block.add_extended_asm(None, "");
 316                     extended_asm.add_input_operand(None, "r", result.llval);
 317                     extended_asm.add_clobber("memory");
 318                     extended_asm.set_volatile_flag(true);
 319
 320                     // We have copied the value to `result` already.
 321                     return;
 322                 }
 323
 324                 _ if name_str.starts_with("simd_") => {
 325                     match generic_simd_intrinsic(self, name, callee_ty, args, ret_ty, llret_ty, span) {
 326                         Ok(llval) => llval,
 327                         Err(()) => return,
 328                     }
 329                 }
 330
 331                 _ => bug!("unknown intrinsic '{}'", name),
 332             };
 333
 334         if !fn_abi.ret.is_ignore() {
 335             if let PassMode::Cast(ty) = fn_abi.ret.mode {
 336                 let ptr_llty = self.type_ptr_to(ty.gcc_type(self));
 337                 let ptr = self.pointercast(result.llval, ptr_llty);
 338                 self.store(llval, ptr, result.align);
 339             }
 340             else {
 341                 OperandRef::from_immediate_or_packed_pair(self, llval, result.layout)
 342                     .val
 343                     .store(self, result);
 344             }
 345         }
 346     }
 347
 348     fn abort(&mut self) {
 349         let func = self.context.get_builtin_function("abort");
 350         let func: RValue<'gcc> = unsafe { std::mem::transmute(func) };
 351         self.call(self.type_void(), func, &[], None);
 352     }
 353
 354     fn assume(&mut self, value: Self::Value) {
 355         // TODO(antoyo): switch to asumme when it exists.
 356         // Or use something like this:
 357         // #define __assume(cond) do { if (!(cond)) __builtin_unreachable(); } while (0)
 358         self.expect(value, true);
 359     }
 360
 361     fn expect(&mut self, cond: Self::Value, _expected: bool) -> Self::Value {
 362         // TODO(antoyo)
 363         cond
 364     }
 365
 366     fn type_test(&mut self, _pointer: Self::Value, _typeid: Self::Value) -> Self::Value {
 367         // Unsupported.
 368         self.context.new_rvalue_from_int(self.int_type, 0)
 369     }
 370
 371     fn va_start(&mut self, _va_list: RValue<'gcc>) -> RValue<'gcc> {
 372         unimplemented!();
 373     }
 374
 375     fn va_end(&mut self, _va_list: RValue<'gcc>) -> RValue<'gcc> {
 376         unimplemented!();
 377     }
 378 }
 379
 380 impl<'a, 'gcc, 'tcx> ArgAbiMethods<'tcx> for Builder<'a, 'gcc, 'tcx> {
 381     fn store_fn_arg(&mut self, arg_abi: &ArgAbi<'tcx, Ty<'tcx>>, idx: &mut usize, dst: PlaceRef<'tcx, Self::Value>) {
 382         arg_abi.store_fn_arg(self, idx, dst)
 383     }
 384
 385     fn store_arg(&mut self, arg_abi: &ArgAbi<'tcx, Ty<'tcx>>, val: RValue<'gcc>, dst: PlaceRef<'tcx, RValue<'gcc>>) {
 386         arg_abi.store(self, val, dst)
 387     }
 388
 389     fn arg_memory_ty(&self, arg_abi: &ArgAbi<'tcx, Ty<'tcx>>) -> Type<'gcc> {
 390         arg_abi.memory_ty(self)
 391     }
 392 }
 393
 394 pub trait ArgAbiExt<'gcc, 'tcx> {
 395     fn memory_ty(&self, cx: &CodegenCx<'gcc, 'tcx>) -> Type<'gcc>;
 396     fn store(&self, bx: &mut Builder<'_, 'gcc, 'tcx>, val: RValue<'gcc>, dst: PlaceRef<'tcx, RValue<'gcc>>);
 397     fn store_fn_arg(&self, bx: &mut Builder<'_, 'gcc, 'tcx>, idx: &mut usize, dst: PlaceRef<'tcx, RValue<'gcc>>);
 398 }
 399
 400 impl<'gcc, 'tcx> ArgAbiExt<'gcc, 'tcx> for ArgAbi<'tcx, Ty<'tcx>> {
 401     /// Gets the LLVM type for a place of the original Rust type of
 402     /// this argument/return, i.e., the result of `type_of::type_of`.
 403     fn memory_ty(&self, cx: &CodegenCx<'gcc, 'tcx>) -> Type<'gcc> {
 404         self.layout.gcc_type(cx, true)
 405     }
 406
 407     /// Stores a direct/indirect value described by this ArgAbi into a
 408     /// place for the original Rust type of this argument/return.
 409     /// Can be used for both storing formal arguments into Rust variables
 410     /// or results of call/invoke instructions into their destinations.
 411     fn store(&self, bx: &mut Builder<'_, 'gcc, 'tcx>, val: RValue<'gcc>, dst: PlaceRef<'tcx, RValue<'gcc>>) {
 412         if self.is_ignore() {
 413             return;
 414         }
 415         if self.is_sized_indirect() {
 416             OperandValue::Ref(val, None, self.layout.align.abi).store(bx, dst)
 417         }
 418         else if self.is_unsized_indirect() {
 419             bug!("unsized `ArgAbi` must be handled through `store_fn_arg`");
 420         }
 421         else if let PassMode::Cast(cast) = self.mode {
 422             // FIXME(eddyb): Figure out when the simpler Store is safe, clang
 423             // uses it for i16 -> {i8, i8}, but not for i24 -> {i8, i8, i8}.
 424             let can_store_through_cast_ptr = false;
 425             if can_store_through_cast_ptr {
 426                 let cast_ptr_llty = bx.type_ptr_to(cast.gcc_type(bx));
 427                 let cast_dst = bx.pointercast(dst.llval, cast_ptr_llty);
 428                 bx.store(val, cast_dst, self.layout.align.abi);
 429             }
 430             else {
 431                 // The actual return type is a struct, but the ABI
 432                 // adaptation code has cast it into some scalar type.  The
 433                 // code that follows is the only reliable way I have
 434                 // found to do a transform like i64 -> {i32,i32}.
 435                 // Basically we dump the data onto the stack then memcpy it.
 436                 //
 437                 // Other approaches I tried:
 438                 // - Casting rust ret pointer to the foreign type and using Store
 439                 //   is (a) unsafe if size of foreign type > size of rust type and
 440                 //   (b) runs afoul of strict aliasing rules, yielding invalid
 441                 //   assembly under -O (specifically, the store gets removed).
 442                 // - Truncating foreign type to correct integral type and then
 443                 //   bitcasting to the struct type yields invalid cast errors.
 444
 445                 // We instead thus allocate some scratch space...
 446                 let scratch_size = cast.size(bx);
 447                 let scratch_align = cast.align(bx);
 448                 let llscratch = bx.alloca(cast.gcc_type(bx), scratch_align);
 449                 bx.lifetime_start(llscratch, scratch_size);
 450
 451                 // ... where we first store the value...
 452                 bx.store(val, llscratch, scratch_align);
 453
 454                 // ... and then memcpy it to the intended destination.
 455                 bx.memcpy(
 456                     dst.llval,
 457                     self.layout.align.abi,
 458                     llscratch,
 459                     scratch_align,
 460                     bx.const_usize(self.layout.size.bytes()),
 461                     MemFlags::empty(),
 462                 );
 463
 464                 bx.lifetime_end(llscratch, scratch_size);
 465             }
 466         }
 467         else {
 468             OperandValue::Immediate(val).store(bx, dst);
 469         }
 470     }
 471
 472     fn store_fn_arg<'a>(&self, bx: &mut Builder<'a, 'gcc, 'tcx>, idx: &mut usize, dst: PlaceRef<'tcx, RValue<'gcc>>) {
 473         let mut next = || {
 474             let val = bx.current_func().get_param(*idx as i32);
 475             *idx += 1;
 476             val.to_rvalue()
 477         };
 478         match self.mode {
 479             PassMode::Ignore => {}
 480             PassMode::Pair(..) => {
 481                 OperandValue::Pair(next(), next()).store(bx, dst);
 482             }
 483             PassMode::Indirect { extra_attrs: Some(_), .. } => {
 484                 OperandValue::Ref(next(), Some(next()), self.layout.align.abi).store(bx, dst);
 485             }
 486             PassMode::Direct(_) | PassMode::Indirect { extra_attrs: None, .. } | PassMode::Cast(_) => {
 487                 let next_arg = next();
 488                 self.store(bx, next_arg.to_rvalue(), dst);
 489             }
 490         }
 491     }
 492 }
 493
 494 fn int_type_width_signed<'gcc, 'tcx>(ty: Ty<'tcx>, cx: &CodegenCx<'gcc, 'tcx>) -> Option<(u64, bool)> {
 495     match ty.kind() {
 496         ty::Int(t) => Some((
 497             match t {
 498                 rustc_middle::ty::IntTy::Isize => u64::from(cx.tcx.sess.target.pointer_width),
 499                 rustc_middle::ty::IntTy::I8 => 8,
 500                 rustc_middle::ty::IntTy::I16 => 16,
 501                 rustc_middle::ty::IntTy::I32 => 32,
 502                 rustc_middle::ty::IntTy::I64 => 64,
 503                 rustc_middle::ty::IntTy::I128 => 128,
 504             },
 505             true,
 506         )),
 507         ty::Uint(t) => Some((
 508             match t {
 509                 rustc_middle::ty::UintTy::Usize => u64::from(cx.tcx.sess.target.pointer_width),
 510                 rustc_middle::ty::UintTy::U8 => 8,
 511                 rustc_middle::ty::UintTy::U16 => 16,
 512                 rustc_middle::ty::UintTy::U32 => 32,
 513                 rustc_middle::ty::UintTy::U64 => 64,
 514                 rustc_middle::ty::UintTy::U128 => 128,
 515             },
 516             false,
 517         )),
 518         _ => None,
 519     }
 520 }
 521
 522 impl<'a, 'gcc, 'tcx> Builder<'a, 'gcc, 'tcx> {
 523     fn bit_reverse(&mut self, width: u64, value: RValue<'gcc>) -> RValue<'gcc> {
 524         let result_type = value.get_type();
 525         let typ = result_type.to_unsigned(self.cx);
 526
 527         let value =
 528             if result_type.is_signed(self.cx) {
 529                 self.context.new_cast(None, value, typ)
 530             }
 531             else {
 532                 value
 533             };
 534
 535         let context = &self.cx.context;
 536         let result =
 537             match width {
 538                 8 => {
 539                     // First step.
 540                     let left = self.and(value, context.new_rvalue_from_int(typ, 0xF0));
 541                     let left = self.lshr(left, context.new_rvalue_from_int(typ, 4));
 542                     let right = self.and(value, context.new_rvalue_from_int(typ, 0x0F));
 543                     let right = self.shl(right, context.new_rvalue_from_int(typ, 4));
 544                     let step1 = self.or(left, right);
 545
 546                     // Second step.
 547                     let left = self.and(step1, context.new_rvalue_from_int(typ, 0xCC));
 548                     let left = self.lshr(left, context.new_rvalue_from_int(typ, 2));
 549                     let right = self.and(step1, context.new_rvalue_from_int(typ, 0x33));
 550                     let right = self.shl(right, context.new_rvalue_from_int(typ, 2));
 551                     let step2 = self.or(left, right);
 552
 553                     // Third step.
 554                     let left = self.and(step2, context.new_rvalue_from_int(typ, 0xAA));
 555                     let left = self.lshr(left, context.new_rvalue_from_int(typ, 1));
 556                     let right = self.and(step2, context.new_rvalue_from_int(typ, 0x55));
 557                     let right = self.shl(right, context.new_rvalue_from_int(typ, 1));
 558                     let step3 = self.or(left, right);
 559
 560                     step3
 561                 },
 562                 16 => {
 563                     // First step.
 564                     let left = self.and(value, context.new_rvalue_from_int(typ, 0x5555));
 565                     let left = self.shl(left, context.new_rvalue_from_int(typ, 1));
 566                     let right = self.and(value, context.new_rvalue_from_int(typ, 0xAAAA));
 567                     let right = self.lshr(right, context.new_rvalue_from_int(typ, 1));
 568                     let step1 = self.or(left, right);
 569
 570                     // Second step.
 571                     let left = self.and(step1, context.new_rvalue_from_int(typ, 0x3333));
 572                     let left = self.shl(left, context.new_rvalue_from_int(typ, 2));
 573                     let right = self.and(step1, context.new_rvalue_from_int(typ, 0xCCCC));
 574                     let right = self.lshr(right, context.new_rvalue_from_int(typ, 2));
 575                     let step2 = self.or(left, right);
 576
 577                     // Third step.
 578                     let left = self.and(step2, context.new_rvalue_from_int(typ, 0x0F0F));
 579                     let left = self.shl(left, context.new_rvalue_from_int(typ, 4));
 580                     let right = self.and(step2, context.new_rvalue_from_int(typ, 0xF0F0));
 581                     let right = self.lshr(right, context.new_rvalue_from_int(typ, 4));
 582                     let step3 = self.or(left, right);
 583
 584                     // Fourth step.
 585                     let left = self.and(step3, context.new_rvalue_from_int(typ, 0x00FF));
 586                     let left = self.shl(left, context.new_rvalue_from_int(typ, 8));
 587                     let right = self.and(step3, context.new_rvalue_from_int(typ, 0xFF00));
 588                     let right = self.lshr(right, context.new_rvalue_from_int(typ, 8));
 589                     let step4 = self.or(left, right);
 590
 591                     step4
 592                 },
 593                 32 => {
 594                     // TODO(antoyo): Refactor with other implementations.
 595                     // First step.
 596                     let left = self.and(value, context.new_rvalue_from_long(typ, 0x55555555));
 597                     let left = self.shl(left, context.new_rvalue_from_long(typ, 1));
 598                     let right = self.and(value, context.new_rvalue_from_long(typ, 0xAAAAAAAA));
 599                     let right = self.lshr(right, context.new_rvalue_from_long(typ, 1));
 600                     let step1 = self.or(left, right);
 601
 602                     // Second step.
 603                     let left = self.and(step1, context.new_rvalue_from_long(typ, 0x33333333));
 604                     let left = self.shl(left, context.new_rvalue_from_long(typ, 2));
 605                     let right = self.and(step1, context.new_rvalue_from_long(typ, 0xCCCCCCCC));
 606                     let right = self.lshr(right, context.new_rvalue_from_long(typ, 2));
 607                     let step2 = self.or(left, right);
 608
 609                     // Third step.
 610                     let left = self.and(step2, context.new_rvalue_from_long(typ, 0x0F0F0F0F));
 611                     let left = self.shl(left, context.new_rvalue_from_long(typ, 4));
 612                     let right = self.and(step2, context.new_rvalue_from_long(typ, 0xF0F0F0F0));
 613                     let right = self.lshr(right, context.new_rvalue_from_long(typ, 4));
 614                     let step3 = self.or(left, right);
 615
 616                     // Fourth step.
 617                     let left = self.and(step3, context.new_rvalue_from_long(typ, 0x00FF00FF));
 618                     let left = self.shl(left, context.new_rvalue_from_long(typ, 8));
 619                     let right = self.and(step3, context.new_rvalue_from_long(typ, 0xFF00FF00));
 620                     let right = self.lshr(right, context.new_rvalue_from_long(typ, 8));
 621                     let step4 = self.or(left, right);
 622
 623                     // Fifth step.
 624                     let left = self.and(step4, context.new_rvalue_from_long(typ, 0x0000FFFF));
 625                     let left = self.shl(left, context.new_rvalue_from_long(typ, 16));
 626                     let right = self.and(step4, context.new_rvalue_from_long(typ, 0xFFFF0000));
 627                     let right = self.lshr(right, context.new_rvalue_from_long(typ, 16));
 628                     let step5 = self.or(left, right);
 629
 630                     step5
 631                 },
 632                 64 => {
 633                     // First step.
 634                     let left = self.shl(value, context.new_rvalue_from_long(typ, 32));
 635                     let right = self.lshr(value, context.new_rvalue_from_long(typ, 32));
 636                     let step1 = self.or(left, right);
 637
 638                     // Second step.
 639                     let left = self.and(step1, context.new_rvalue_from_long(typ, 0x0001FFFF0001FFFF));
 640                     let left = self.shl(left, context.new_rvalue_from_long(typ, 15));
 641                     let right = self.and(step1, context.new_rvalue_from_long(typ, 0xFFFE0000FFFE0000u64 as i64)); // TODO(antoyo): transmute the number instead?
 642                     let right = self.lshr(right, context.new_rvalue_from_long(typ, 17));
 643                     let step2 = self.or(left, right);
 644
 645                     // Third step.
 646                     let left = self.lshr(step2, context.new_rvalue_from_long(typ, 10));
 647                     let left = self.xor(step2, left);
 648                     let temp = self.and(left, context.new_rvalue_from_long(typ, 0x003F801F003F801F));
 649
 650                     let left = self.shl(temp, context.new_rvalue_from_long(typ, 10));
 651                     let left = self.or(temp, left);
 652                     let step3 = self.xor(left, step2);
 653
 654                     // Fourth step.
 655                     let left = self.lshr(step3, context.new_rvalue_from_long(typ, 4));
 656                     let left = self.xor(step3, left);
 657                     let temp = self.and(left, context.new_rvalue_from_long(typ, 0x0E0384210E038421));
 658
 659                     let left = self.shl(temp, context.new_rvalue_from_long(typ, 4));
 660                     let left = self.or(temp, left);
 661                     let step4 = self.xor(left, step3);
 662
 663                     // Fifth step.
 664                     let left = self.lshr(step4, context.new_rvalue_from_long(typ, 2));
 665                     let left = self.xor(step4, left);
 666                     let temp = self.and(left, context.new_rvalue_from_long(typ, 0x2248884222488842));
 667
 668                     let left = self.shl(temp, context.new_rvalue_from_long(typ, 2));
 669                     let left = self.or(temp, left);
 670                     let step5 = self.xor(left, step4);
 671
 672                     step5
 673                 },
 674                 128 => {
 675                     // TODO(antoyo): find a more efficient implementation?
 676                     let sixty_four = self.context.new_rvalue_from_long(typ, 64);
 677                     let high = self.context.new_cast(None, value >> sixty_four, self.u64_type);
 678                     let low = self.context.new_cast(None, value, self.u64_type);
 679
 680                     let reversed_high = self.bit_reverse(64, high);
 681                     let reversed_low = self.bit_reverse(64, low);
 682
 683                     let new_low = self.context.new_cast(None, reversed_high, typ);
 684                     let new_high = self.context.new_cast(None, reversed_low, typ) << sixty_four;
 685
 686                     new_low | new_high
 687                 },
 688                 _ => {
 689                     panic!("cannot bit reverse with width = {}", width);
 690                 },
 691             };
 692
 693         self.context.new_cast(None, result, result_type)
 694     }
 695
 696     fn count_leading_zeroes(&self, width: u64, arg: RValue<'gcc>) -> RValue<'gcc> {
 697         // TODO(antoyo): use width?
 698         let arg_type = arg.get_type();
 699         let count_leading_zeroes =
 700             if arg_type.is_uint(&self.cx) {
 701                 "__builtin_clz"
 702             }
 703             else if arg_type.is_ulong(&self.cx) {
 704                 "__builtin_clzl"
 705             }
 706             else if arg_type.is_ulonglong(&self.cx) {
 707                 "__builtin_clzll"
 708             }
 709             else if width == 128 {
 710                 // Algorithm from: https://stackoverflow.com/a/28433850/389119
 711                 let array_type = self.context.new_array_type(None, arg_type, 3);
 712                 let result = self.current_func()
 713                     .new_local(None, array_type, "count_loading_zeroes_results");
 714
 715                 let sixty_four = self.context.new_rvalue_from_long(arg_type, 64);
 716                 let high = self.context.new_cast(None, arg >> sixty_four, self.u64_type);
 717                 let low = self.context.new_cast(None, arg, self.u64_type);
 718
 719                 let zero = self.context.new_rvalue_zero(self.usize_type);
 720                 let one = self.context.new_rvalue_one(self.usize_type);
 721                 let two = self.context.new_rvalue_from_long(self.usize_type, 2);
 722
 723                 let clzll = self.context.get_builtin_function("__builtin_clzll");
 724
 725                 let first_elem = self.context.new_array_access(None, result, zero);
 726                 let first_value = self.context.new_cast(None, self.context.new_call(None, clzll, &[high]), arg_type);
 727                 self.llbb()
 728                     .add_assignment(None, first_elem, first_value);
 729
 730                 let second_elem = self.context.new_array_access(None, result, one);
 731                 let second_value = self.context.new_cast(None, self.context.new_call(None, clzll, &[low]), arg_type) + sixty_four;
 732                 self.llbb()
 733                     .add_assignment(None, second_elem, second_value);
 734
 735                 let third_elem = self.context.new_array_access(None, result, two);
 736                 let third_value = self.context.new_rvalue_from_long(arg_type, 128);
 737                 self.llbb()
 738                     .add_assignment(None, third_elem, third_value);
 739
 740                 let not_high = self.context.new_unary_op(None, UnaryOp::LogicalNegate, self.u64_type, high);
 741                 let not_low = self.context.new_unary_op(None, UnaryOp::LogicalNegate, self.u64_type, low);
 742                 let not_low_and_not_high = not_low & not_high;
 743                 let index = not_high + not_low_and_not_high;
 744                 // NOTE: the following cast is necessary to avoid a GIMPLE verification failure in
 745                 // gcc.
 746                 // TODO(antoyo): do the correct verification in libgccjit to avoid an error at the
 747                 // compilation stage.
 748                 let index = self.context.new_cast(None, index, self.i32_type);
 749
 750                 let res = self.context.new_array_access(None, result, index);
 751
 752                 return self.context.new_cast(None, res, arg_type);
 753             }
 754             else {
 755                 let count_leading_zeroes = self.context.get_builtin_function("__builtin_clz");
 756                 let arg = self.context.new_cast(None, arg, self.uint_type);
 757                 let diff = self.int_width(self.uint_type) - self.int_width(arg_type);
 758                 let diff = self.context.new_rvalue_from_long(self.int_type, diff);
 759                 let res = self.context.new_call(None, count_leading_zeroes, &[arg]) - diff;
 760                 return self.context.new_cast(None, res, arg_type);
 761             };
 762         let count_leading_zeroes = self.context.get_builtin_function(count_leading_zeroes);
 763         let res = self.context.new_call(None, count_leading_zeroes, &[arg]);
 764         self.context.new_cast(None, res, arg_type)
 765     }
 766
 767     fn count_trailing_zeroes(&self, _width: u64, arg: RValue<'gcc>) -> RValue<'gcc> {
 768         let result_type = arg.get_type();
 769         let arg =
 770             if result_type.is_signed(self.cx) {
 771                 let new_type = result_type.to_unsigned(self.cx);
 772                 self.context.new_cast(None, arg, new_type)
 773             }
 774             else {
 775                 arg
 776             };
 777         let arg_type = arg.get_type();
 778         let (count_trailing_zeroes, expected_type) =
 779             if arg_type.is_uchar(&self.cx) || arg_type.is_ushort(&self.cx) || arg_type.is_uint(&self.cx) {
 780                 // NOTE: we don't need to & 0xFF for uchar because the result is undefined on zero.
 781                 ("__builtin_ctz", self.cx.uint_type)
 782             }
 783             else if arg_type.is_ulong(&self.cx) {
 784                 ("__builtin_ctzl", self.cx.ulong_type)
 785             }
 786             else if arg_type.is_ulonglong(&self.cx) {
 787                 ("__builtin_ctzll", self.cx.ulonglong_type)
 788             }
 789             else if arg_type.is_u128(&self.cx) {
 790                 // Adapted from the algorithm to count leading zeroes from: https://stackoverflow.com/a/28433850/389119
 791                 let array_type = self.context.new_array_type(None, arg_type, 3);
 792                 let result = self.current_func()
 793                     .new_local(None, array_type, "count_loading_zeroes_results");
 794
 795                 let sixty_four = self.context.new_rvalue_from_long(arg_type, 64);
 796                 let high = self.context.new_cast(None, arg >> sixty_four, self.u64_type);
 797                 let low = self.context.new_cast(None, arg, self.u64_type);
 798
 799                 let zero = self.context.new_rvalue_zero(self.usize_type);
 800                 let one = self.context.new_rvalue_one(self.usize_type);
 801                 let two = self.context.new_rvalue_from_long(self.usize_type, 2);
 802
 803                 let ctzll = self.context.get_builtin_function("__builtin_ctzll");
 804
 805                 let first_elem = self.context.new_array_access(None, result, zero);
 806                 let first_value = self.context.new_cast(None, self.context.new_call(None, ctzll, &[low]), arg_type);
 807                 self.llbb()
 808                     .add_assignment(None, first_elem, first_value);
 809
 810                 let second_elem = self.context.new_array_access(None, result, one);
 811                 let second_value = self.context.new_cast(None, self.context.new_call(None, ctzll, &[high]), arg_type) + sixty_four;
 812                 self.llbb()
 813                     .add_assignment(None, second_elem, second_value);
 814
 815                 let third_elem = self.context.new_array_access(None, result, two);
 816                 let third_value = self.context.new_rvalue_from_long(arg_type, 128);
 817                 self.llbb()
 818                     .add_assignment(None, third_elem, third_value);
 819
 820                 let not_low = self.context.new_unary_op(None, UnaryOp::LogicalNegate, self.u64_type, low);
 821                 let not_high = self.context.new_unary_op(None, UnaryOp::LogicalNegate, self.u64_type, high);
 822                 let not_low_and_not_high = not_low & not_high;
 823                 let index = not_low + not_low_and_not_high;
 824                 // NOTE: the following cast is necessary to avoid a GIMPLE verification failure in
 825                 // gcc.
 826                 // TODO(antoyo): do the correct verification in libgccjit to avoid an error at the
 827                 // compilation stage.
 828                 let index = self.context.new_cast(None, index, self.i32_type);
 829
 830                 let res = self.context.new_array_access(None, result, index);
 831
 832                 return self.context.new_cast(None, res, result_type);
 833             }
 834             else {
 835                 unimplemented!("count_trailing_zeroes for {:?}", arg_type);
 836             };
 837         let count_trailing_zeroes = self.context.get_builtin_function(count_trailing_zeroes);
 838         let arg =
 839             if arg_type != expected_type {
 840                 self.context.new_cast(None, arg, expected_type)
 841             }
 842             else {
 843                 arg
 844             };
 845         let res = self.context.new_call(None, count_trailing_zeroes, &[arg]);
 846         self.context.new_cast(None, res, result_type)
 847     }
 848
 849     fn int_width(&self, typ: Type<'gcc>) -> i64 {
 850         self.cx.int_width(typ) as i64
 851     }
 852
 853     fn pop_count(&self, value: RValue<'gcc>) -> RValue<'gcc> {
 854         // TODO(antoyo): use the optimized version with fewer operations.
 855         let result_type = value.get_type();
 856         let value_type = result_type.to_unsigned(self.cx);
 857
 858         let value =
 859             if result_type.is_signed(self.cx) {
 860                 self.context.new_cast(None, value, value_type)
 861             }
 862             else {
 863                 value
 864             };
 865
 866         if value_type.is_u128(&self.cx) {
 867             // TODO(antoyo): implement in the normal algorithm below to have a more efficient
 868             // implementation (that does not require a call to __popcountdi2).
 869             let popcount = self.context.get_builtin_function("__builtin_popcountll");
 870             let sixty_four = self.context.new_rvalue_from_long(value_type, 64);
 871             let high = self.context.new_cast(None, value >> sixty_four, self.cx.ulonglong_type);
 872             let high = self.context.new_call(None, popcount, &[high]);
 873             let low = self.context.new_cast(None, value, self.cx.ulonglong_type);
 874             let low = self.context.new_call(None, popcount, &[low]);
 875             let res = high + low;
 876             return self.context.new_cast(None, res, result_type);
 877         }
 878
 879         // First step.
 880         let mask = self.context.new_rvalue_from_long(value_type, 0x5555555555555555);
 881         let left = value & mask;
 882         let shifted = value >> self.context.new_rvalue_from_int(value_type, 1);
 883         let right = shifted & mask;
 884         let value = left + right;
 885
 886         // Second step.
 887         let mask = self.context.new_rvalue_from_long(value_type, 0x3333333333333333);
 888         let left = value & mask;
 889         let shifted = value >> self.context.new_rvalue_from_int(value_type, 2);
 890         let right = shifted & mask;
 891         let value = left + right;
 892
 893         // Third step.
 894         let mask = self.context.new_rvalue_from_long(value_type, 0x0F0F0F0F0F0F0F0F);
 895         let left = value & mask;
 896         let shifted = value >> self.context.new_rvalue_from_int(value_type, 4);
 897         let right = shifted & mask;
 898         let value = left + right;
 899
 900         if value_type.is_u8(&self.cx) {
 901             return self.context.new_cast(None, value, result_type);
 902         }
 903
 904         // Fourth step.
 905         let mask = self.context.new_rvalue_from_long(value_type, 0x00FF00FF00FF00FF);
 906         let left = value & mask;
 907         let shifted = value >> self.context.new_rvalue_from_int(value_type, 8);
 908         let right = shifted & mask;
 909         let value = left + right;
 910
 911         if value_type.is_u16(&self.cx) {
 912             return self.context.new_cast(None, value, result_type);
 913         }
 914
 915         // Fifth step.
 916         let mask = self.context.new_rvalue_from_long(value_type, 0x0000FFFF0000FFFF);
 917         let left = value & mask;
 918         let shifted = value >> self.context.new_rvalue_from_int(value_type, 16);
 919         let right = shifted & mask;
 920         let value = left + right;
 921
 922         if value_type.is_u32(&self.cx) {
 923             return self.context.new_cast(None, value, result_type);
 924         }
 925
 926         // Sixth step.
 927         let mask = self.context.new_rvalue_from_long(value_type, 0x00000000FFFFFFFF);
 928         let left = value & mask;
 929         let shifted = value >> self.context.new_rvalue_from_int(value_type, 32);
 930         let right = shifted & mask;
 931         let value = left + right;
 932
 933         self.context.new_cast(None, value, result_type)
 934     }
 935
 936     // Algorithm from: https://blog.regehr.org/archives/1063
 937     fn rotate_left(&mut self, value: RValue<'gcc>, shift: RValue<'gcc>, width: u64) -> RValue<'gcc> {
 938         let max = self.context.new_rvalue_from_long(shift.get_type(), width as i64);
 939         let shift = shift % max;
 940         let lhs = self.shl(value, shift);
 941         let result_and =
 942             self.and(
 943                 self.context.new_unary_op(None, UnaryOp::Minus, shift.get_type(), shift),
 944                 self.context.new_rvalue_from_long(shift.get_type(), width as i64 - 1),
 945             );
 946         let rhs = self.lshr(value, result_and);
 947         self.or(lhs, rhs)
 948     }
 949
 950     // Algorithm from: https://blog.regehr.org/archives/1063
 951     fn rotate_right(&mut self, value: RValue<'gcc>, shift: RValue<'gcc>, width: u64) -> RValue<'gcc> {
 952         let max = self.context.new_rvalue_from_long(shift.get_type(), width as i64);
 953         let shift = shift % max;
 954         let lhs = self.lshr(value, shift);
 955         let result_and =
 956             self.and(
 957                 self.context.new_unary_op(None, UnaryOp::Minus, shift.get_type(), shift),
 958                 self.context.new_rvalue_from_long(shift.get_type(), width as i64 - 1),
 959             );
 960         let rhs = self.shl(value, result_and);
 961         self.or(lhs, rhs)
 962     }
 963
 964     fn saturating_add(&mut self, lhs: RValue<'gcc>, rhs: RValue<'gcc>, signed: bool, width: u64) -> RValue<'gcc> {
 965         let func = self.current_func.borrow().expect("func");
 966
 967         if signed {
 968             // Algorithm from: https://stackoverflow.com/a/56531252/389119
 969             let after_block = func.new_block("after");
 970             let func_name =
 971                 match width {
 972                     8 => "__builtin_add_overflow",
 973                     16 => "__builtin_add_overflow",
 974                     32 => "__builtin_sadd_overflow",
 975                     64 => "__builtin_saddll_overflow",
 976                     128 => "__builtin_add_overflow",
 977                     _ => unreachable!(),
 978                 };
 979             let overflow_func = self.context.get_builtin_function(func_name);
 980             let result_type = lhs.get_type();
 981             let res = func.new_local(None, result_type, "saturating_sum");
 982             let overflow = self.overflow_call(overflow_func, &[lhs, rhs, res.get_address(None)], None);
 983
 984             let then_block = func.new_block("then");
 985
 986             let unsigned_type = self.context.new_int_type(width as i32 / 8, false);
 987             let shifted = self.context.new_cast(None, lhs, unsigned_type) >> self.context.new_rvalue_from_int(unsigned_type, width as i32 - 1);
 988             let uint_max = self.context.new_unary_op(None, UnaryOp::BitwiseNegate, unsigned_type,
 989                 self.context.new_rvalue_from_int(unsigned_type, 0)
 990             );
 991             let int_max = uint_max >> self.context.new_rvalue_one(unsigned_type);
 992             then_block.add_assignment(None, res, self.context.new_cast(None, shifted + int_max, result_type));
 993             then_block.end_with_jump(None, after_block);
 994
 995             self.llbb().end_with_conditional(None, overflow, then_block, after_block);
 996
 997             // NOTE: since jumps were added in a place rustc does not
 998             // expect, the current blocks in the state need to be updated.
 999             *self.current_block.borrow_mut() = Some(after_block);
1000             self.block = Some(after_block);
1001
1002             res.to_rvalue()
1003         }
1004         else {
1005             // Algorithm from: http://locklessinc.com/articles/sat_arithmetic/
1006             let res = lhs + rhs;
1007             let res_type = res.get_type();
1008             let cond = self.context.new_comparison(None, ComparisonOp::LessThan, res, lhs);
1009             let value = self.context.new_unary_op(None, UnaryOp::Minus, res_type, self.context.new_cast(None, cond, res_type));
1010             res | value
1011         }
1012     }
1013
1014     // Algorithm from: https://locklessinc.com/articles/sat_arithmetic/
1015     fn saturating_sub(&mut self, lhs: RValue<'gcc>, rhs: RValue<'gcc>, signed: bool, width: u64) -> RValue<'gcc> {
1016         if signed {
1017             // Also based on algorithm from: https://stackoverflow.com/a/56531252/389119
1018             let func_name =
1019                 match width {
1020                     8 => "__builtin_sub_overflow",
1021                     16 => "__builtin_sub_overflow",
1022                     32 => "__builtin_ssub_overflow",
1023                     64 => "__builtin_ssubll_overflow",
1024                     128 => "__builtin_sub_overflow",
1025                     _ => unreachable!(),
1026                 };
1027             let overflow_func = self.context.get_builtin_function(func_name);
1028             let result_type = lhs.get_type();
1029             let func = self.current_func.borrow().expect("func");
1030             let res = func.new_local(None, result_type, "saturating_diff");
1031             let overflow = self.overflow_call(overflow_func, &[lhs, rhs, res.get_address(None)], None);
1032
1033             let then_block = func.new_block("then");
1034             let after_block = func.new_block("after");
1035
1036             let unsigned_type = self.context.new_int_type(width as i32 / 8, false);
1037             let shifted = self.context.new_cast(None, lhs, unsigned_type) >> self.context.new_rvalue_from_int(unsigned_type, width as i32 - 1);
1038             let uint_max = self.context.new_unary_op(None, UnaryOp::BitwiseNegate, unsigned_type,
1039                 self.context.new_rvalue_from_int(unsigned_type, 0)
1040             );
1041             let int_max = uint_max >> self.context.new_rvalue_one(unsigned_type);
1042             then_block.add_assignment(None, res, self.context.new_cast(None, shifted + int_max, result_type));
1043             then_block.end_with_jump(None, after_block);
1044
1045             self.llbb().end_with_conditional(None, overflow, then_block, after_block);
1046
1047             // NOTE: since jumps were added in a place rustc does not
1048             // expect, the current blocks in the state need to be updated.
1049             *self.current_block.borrow_mut() = Some(after_block);
1050             self.block = Some(after_block);
1051
1052             res.to_rvalue()
1053         }
1054         else {
1055             let res = lhs - rhs;
1056             let comparison = self.context.new_comparison(None, ComparisonOp::LessThanEquals, res, lhs);
1057             let comparison = self.context.new_cast(None, comparison, lhs.get_type());
1058             let unary_op = self.context.new_unary_op(None, UnaryOp::Minus, comparison.get_type(), comparison);
1059             self.and(res, unary_op)
1060         }
1061     }
1062 }
1063
1064 fn try_intrinsic<'gcc, 'tcx>(bx: &mut Builder<'_, 'gcc, 'tcx>, try_func: RValue<'gcc>, data: RValue<'gcc>, _catch_func: RValue<'gcc>, dest: RValue<'gcc>) {
1065     if bx.sess().panic_strategy() == PanicStrategy::Abort {
1066         bx.call(bx.type_void(), try_func, &[data], None);
1067         // Return 0 unconditionally from the intrinsic call;
1068         // we can never unwind.
1069         let ret_align = bx.tcx.data_layout.i32_align.abi;
1070         bx.store(bx.const_i32(0), dest, ret_align);
1071     }
1072     else if wants_msvc_seh(bx.sess()) {
1073         unimplemented!();
1074     }
1075     else {
1076         unimplemented!();
1077     }
1078 }