1 use rustc::ty::{self, Ty, adjustment::{PointerCast}, Instance};
2 use rustc::ty::cast::{CastTy, IntTy};
3 use rustc::ty::layout::{self, LayoutOf, HasTyCtxt};
5 use rustc::middle::lang_items::ExchangeMallocFnLangItem;
6 use rustc_apfloat::{ieee, Float, Status, Round};
8 use syntax::symbol::sym;
13 use crate::common::{self, RealPredicate, IntPredicate};
17 use super::{FunctionCx, LocalRef};
18 use super::operand::{OperandRef, OperandValue};
19 use super::place::PlaceRef;
21 impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
22 pub fn codegen_rvalue(
25 dest: PlaceRef<'tcx, Bx::Value>,
26 rvalue: &mir::Rvalue<'tcx>
28 debug!("codegen_rvalue(dest.llval={:?}, rvalue={:?})",
32 mir::Rvalue::Use(ref operand) => {
33 let cg_operand = self.codegen_operand(&mut bx, operand);
34 // FIXME: consider not copying constants through stack. (fixable by codegenning
35 // constants into OperandValue::Ref, why don’t we do that yet if we don’t?)
36 cg_operand.val.store(&mut bx, dest);
40 mir::Rvalue::Cast(mir::CastKind::Pointer(PointerCast::Unsize), ref source, _) => {
41 // The destination necessarily contains a fat pointer, so if
42 // it's a scalar pair, it's a fat pointer or newtype thereof.
43 if bx.cx().is_backend_scalar_pair(dest.layout) {
44 // into-coerce of a thin pointer to a fat pointer - just
45 // use the operand path.
46 let (mut bx, temp) = self.codegen_rvalue_operand(bx, rvalue);
47 temp.val.store(&mut bx, dest);
51 // Unsize of a nontrivial struct. I would prefer for
52 // this to be eliminated by MIR building, but
53 // `CoerceUnsized` can be passed by a where-clause,
54 // so the (generic) MIR may not be able to expand it.
55 let operand = self.codegen_operand(&mut bx, source);
57 OperandValue::Pair(..) |
58 OperandValue::Immediate(_) => {
59 // unsize from an immediate structure. We don't
60 // really need a temporary alloca here, but
61 // avoiding it would require us to have
62 // `coerce_unsized_into` use extractvalue to
63 // index into the struct, and this case isn't
64 // important enough for it.
65 debug!("codegen_rvalue: creating ugly alloca");
66 let scratch = PlaceRef::alloca(&mut bx, operand.layout, "__unsize_temp");
67 scratch.storage_live(&mut bx);
68 operand.val.store(&mut bx, scratch);
69 base::coerce_unsized_into(&mut bx, scratch, dest);
70 scratch.storage_dead(&mut bx);
72 OperandValue::Ref(llref, None, align) => {
73 let source = PlaceRef::new_sized(llref, operand.layout, align);
74 base::coerce_unsized_into(&mut bx, source, dest);
76 OperandValue::Ref(_, Some(_), _) => {
77 bug!("unsized coercion on an unsized rvalue")
83 mir::Rvalue::Repeat(ref elem, count) => {
84 let cg_elem = self.codegen_operand(&mut bx, elem);
86 // Do not generate the loop for zero-sized elements or empty arrays.
87 if dest.layout.is_zst() {
91 if let OperandValue::Immediate(v) = cg_elem.val {
92 let zero = bx.const_usize(0);
93 let start = dest.project_index(&mut bx, zero).llval;
94 let size = bx.const_usize(dest.layout.size.bytes());
96 // Use llvm.memset.p0i8.* to initialize all zero arrays
97 if bx.cx().is_const_integral(v) && bx.cx().const_to_uint(v) == 0 {
98 let fill = bx.cx().const_u8(0);
99 bx.memset(start, fill, size, dest.align, MemFlags::empty());
103 // Use llvm.memset.p0i8.* to initialize byte arrays
104 let v = base::from_immediate(&mut bx, v);
105 if bx.cx().val_ty(v) == bx.cx().type_i8() {
106 bx.memset(start, v, size, dest.align, MemFlags::empty());
111 bx.write_operand_repeatedly(cg_elem, count, dest)
114 mir::Rvalue::Aggregate(ref kind, ref operands) => {
115 let (dest, active_field_index) = match **kind {
116 mir::AggregateKind::Adt(adt_def, variant_index, _, _, active_field_index) => {
117 dest.codegen_set_discr(&mut bx, variant_index);
118 if adt_def.is_enum() {
119 (dest.project_downcast(&mut bx, variant_index), active_field_index)
121 (dest, active_field_index)
126 for (i, operand) in operands.iter().enumerate() {
127 let op = self.codegen_operand(&mut bx, operand);
128 // Do not generate stores and GEPis for zero-sized fields.
129 if !op.layout.is_zst() {
130 let field_index = active_field_index.unwrap_or(i);
131 let field = dest.project_field(&mut bx, field_index);
132 op.val.store(&mut bx, field);
139 assert!(self.rvalue_creates_operand(rvalue));
140 let (mut bx, temp) = self.codegen_rvalue_operand(bx, rvalue);
141 temp.val.store(&mut bx, dest);
147 pub fn codegen_rvalue_unsized(
150 indirect_dest: PlaceRef<'tcx, Bx::Value>,
151 rvalue: &mir::Rvalue<'tcx>,
153 debug!("codegen_rvalue_unsized(indirect_dest.llval={:?}, rvalue={:?})",
154 indirect_dest.llval, rvalue);
157 mir::Rvalue::Use(ref operand) => {
158 let cg_operand = self.codegen_operand(&mut bx, operand);
159 cg_operand.val.store_unsized(&mut bx, indirect_dest);
163 _ => bug!("unsized assignment other than Rvalue::Use"),
167 pub fn codegen_rvalue_operand(
170 rvalue: &mir::Rvalue<'tcx>
171 ) -> (Bx, OperandRef<'tcx, Bx::Value>) {
172 assert!(self.rvalue_creates_operand(rvalue), "cannot codegen {:?} to operand", rvalue);
175 mir::Rvalue::Cast(ref kind, ref source, mir_cast_ty) => {
176 let operand = self.codegen_operand(&mut bx, source);
177 debug!("cast operand is {:?}", operand);
178 let cast = bx.cx().layout_of(self.monomorphize(&mir_cast_ty));
180 let val = match *kind {
181 mir::CastKind::Pointer(PointerCast::ReifyFnPointer) => {
182 match operand.layout.ty.sty {
183 ty::FnDef(def_id, substs) => {
184 if bx.cx().tcx().has_attr(def_id, sym::rustc_args_required_const) {
185 bug!("reifying a fn ptr that requires const arguments");
187 OperandValue::Immediate(
188 callee::resolve_and_get_fn(bx.cx(), def_id, substs))
191 bug!("{} cannot be reified to a fn ptr", operand.layout.ty)
195 mir::CastKind::Pointer(PointerCast::ClosureFnPointer(_)) => {
196 match operand.layout.ty.sty {
197 ty::Closure(def_id, substs) => {
198 let instance = Instance::resolve_closure(
199 bx.cx().tcx(), def_id, substs, ty::ClosureKind::FnOnce);
200 OperandValue::Immediate(bx.cx().get_fn(instance))
203 bug!("{} cannot be cast to a fn ptr", operand.layout.ty)
207 mir::CastKind::Pointer(PointerCast::UnsafeFnPointer) => {
208 // this is a no-op at the LLVM level
211 mir::CastKind::Pointer(PointerCast::Unsize) => {
212 assert!(bx.cx().is_backend_scalar_pair(cast));
214 OperandValue::Pair(lldata, llextra) => {
215 // unsize from a fat pointer - this is a
216 // "trait-object-to-supertrait" coercion, for
218 // &'a fmt::Debug+Send => &'a fmt::Debug,
220 // HACK(eddyb) have to bitcast pointers
221 // until LLVM removes pointee types.
222 let lldata = bx.pointercast(lldata,
223 bx.cx().scalar_pair_element_backend_type(cast, 0, true));
224 OperandValue::Pair(lldata, llextra)
226 OperandValue::Immediate(lldata) => {
228 let (lldata, llextra) = base::unsize_thin_ptr(&mut bx, lldata,
229 operand.layout.ty, cast.ty);
230 OperandValue::Pair(lldata, llextra)
232 OperandValue::Ref(..) => {
233 bug!("by-ref operand {:?} in codegen_rvalue_operand",
238 mir::CastKind::Pointer(PointerCast::MutToConstPointer)
239 | mir::CastKind::Misc if bx.cx().is_backend_scalar_pair(operand.layout) => {
240 if let OperandValue::Pair(data_ptr, meta) = operand.val {
241 if bx.cx().is_backend_scalar_pair(cast) {
242 let data_cast = bx.pointercast(data_ptr,
243 bx.cx().scalar_pair_element_backend_type(cast, 0, true));
244 OperandValue::Pair(data_cast, meta)
245 } else { // cast to thin-ptr
246 // Cast of fat-ptr to thin-ptr is an extraction of data-ptr and
247 // pointer-cast of that pointer to desired pointer type.
248 let llcast_ty = bx.cx().immediate_backend_type(cast);
249 let llval = bx.pointercast(data_ptr, llcast_ty);
250 OperandValue::Immediate(llval)
253 bug!("Unexpected non-Pair operand")
256 mir::CastKind::Pointer(PointerCast::MutToConstPointer)
257 | mir::CastKind::Misc => {
258 assert!(bx.cx().is_backend_immediate(cast));
259 let ll_t_out = bx.cx().immediate_backend_type(cast);
260 if operand.layout.abi.is_uninhabited() {
261 let val = OperandValue::Immediate(bx.cx().const_undef(ll_t_out));
262 return (bx, OperandRef {
267 let r_t_in = CastTy::from_ty(operand.layout.ty)
268 .expect("bad input type for cast");
269 let r_t_out = CastTy::from_ty(cast.ty).expect("bad output type for cast");
270 let ll_t_in = bx.cx().immediate_backend_type(operand.layout);
271 match operand.layout.variants {
272 layout::Variants::Single { index } => {
274 operand.layout.ty.discriminant_for_variant(bx.tcx(), index)
276 let discr_val = bx.cx().const_uint_big(ll_t_out, discr.val);
277 return (bx, OperandRef {
278 val: OperandValue::Immediate(discr_val),
283 layout::Variants::Multiple { .. } => {},
285 let llval = operand.immediate();
287 let mut signed = false;
288 if let layout::Abi::Scalar(ref scalar) = operand.layout.abi {
289 if let layout::Int(_, s) = scalar.value {
290 // We use `i1` for bytes that are always `0` or `1`,
291 // e.g., `#[repr(i8)] enum E { A, B }`, but we can't
292 // let LLVM interpret the `i1` as signed, because
293 // then `i1 1` (i.e., E::B) is effectively `i8 -1`.
294 signed = !scalar.is_bool() && s;
296 let er = scalar.valid_range_exclusive(bx.cx());
297 if er.end != er.start &&
298 scalar.valid_range.end() > scalar.valid_range.start() {
299 // We want `table[e as usize]` to not
300 // have bound checks, and this is the most
301 // convenient place to put the `assume`.
303 bx.cx().const_uint_big(ll_t_in, *scalar.valid_range.end());
305 IntPredicate::IntULE,
314 let newval = match (r_t_in, r_t_out) {
315 (CastTy::Int(_), CastTy::Int(_)) => {
316 bx.intcast(llval, ll_t_out, signed)
318 (CastTy::Float, CastTy::Float) => {
319 let srcsz = bx.cx().float_width(ll_t_in);
320 let dstsz = bx.cx().float_width(ll_t_out);
322 bx.fpext(llval, ll_t_out)
323 } else if srcsz > dstsz {
324 bx.fptrunc(llval, ll_t_out)
329 (CastTy::Ptr(_), CastTy::Ptr(_)) |
330 (CastTy::FnPtr, CastTy::Ptr(_)) |
331 (CastTy::RPtr(_), CastTy::Ptr(_)) =>
332 bx.pointercast(llval, ll_t_out),
333 (CastTy::Ptr(_), CastTy::Int(_)) |
334 (CastTy::FnPtr, CastTy::Int(_)) =>
335 bx.ptrtoint(llval, ll_t_out),
336 (CastTy::Int(_), CastTy::Ptr(_)) => {
337 let usize_llval = bx.intcast(llval, bx.cx().type_isize(), signed);
338 bx.inttoptr(usize_llval, ll_t_out)
340 (CastTy::Int(_), CastTy::Float) =>
341 cast_int_to_float(&mut bx, signed, llval, ll_t_in, ll_t_out),
342 (CastTy::Float, CastTy::Int(IntTy::I)) =>
343 cast_float_to_int(&mut bx, true, llval, ll_t_in, ll_t_out),
344 (CastTy::Float, CastTy::Int(_)) =>
345 cast_float_to_int(&mut bx, false, llval, ll_t_in, ll_t_out),
346 _ => bug!("unsupported cast: {:?} to {:?}", operand.layout.ty, cast.ty)
348 OperandValue::Immediate(newval)
357 mir::Rvalue::Ref(_, bk, ref place) => {
358 let cg_place = self.codegen_place(&mut bx, &place.as_ref());
360 let ty = cg_place.layout.ty;
362 // Note: places are indirect, so storing the `llval` into the
363 // destination effectively creates a reference.
364 let val = if !bx.cx().type_has_metadata(ty) {
365 OperandValue::Immediate(cg_place.llval)
367 OperandValue::Pair(cg_place.llval, cg_place.llextra.unwrap())
371 layout: self.cx.layout_of(self.cx.tcx().mk_ref(
372 self.cx.tcx().lifetimes.re_erased,
373 ty::TypeAndMut { ty, mutbl: bk.to_mutbl_lossy() }
378 mir::Rvalue::Len(ref place) => {
379 let size = self.evaluate_array_len(&mut bx, place);
380 let operand = OperandRef {
381 val: OperandValue::Immediate(size),
382 layout: bx.cx().layout_of(bx.tcx().types.usize),
387 mir::Rvalue::BinaryOp(op, ref lhs, ref rhs) => {
388 let lhs = self.codegen_operand(&mut bx, lhs);
389 let rhs = self.codegen_operand(&mut bx, rhs);
390 let llresult = match (lhs.val, rhs.val) {
391 (OperandValue::Pair(lhs_addr, lhs_extra),
392 OperandValue::Pair(rhs_addr, rhs_extra)) => {
393 self.codegen_fat_ptr_binop(&mut bx, op,
399 (OperandValue::Immediate(lhs_val),
400 OperandValue::Immediate(rhs_val)) => {
401 self.codegen_scalar_binop(&mut bx, op, lhs_val, rhs_val, lhs.layout.ty)
406 let operand = OperandRef {
407 val: OperandValue::Immediate(llresult),
408 layout: bx.cx().layout_of(
409 op.ty(bx.tcx(), lhs.layout.ty, rhs.layout.ty)),
413 mir::Rvalue::CheckedBinaryOp(op, ref lhs, ref rhs) => {
414 let lhs = self.codegen_operand(&mut bx, lhs);
415 let rhs = self.codegen_operand(&mut bx, rhs);
416 let result = self.codegen_scalar_checked_binop(&mut bx, op,
417 lhs.immediate(), rhs.immediate(),
419 let val_ty = op.ty(bx.tcx(), lhs.layout.ty, rhs.layout.ty);
420 let operand_ty = bx.tcx().intern_tup(&[val_ty, bx.tcx().types.bool]);
421 let operand = OperandRef {
423 layout: bx.cx().layout_of(operand_ty)
429 mir::Rvalue::UnaryOp(op, ref operand) => {
430 let operand = self.codegen_operand(&mut bx, operand);
431 let lloperand = operand.immediate();
432 let is_float = operand.layout.ty.is_floating_point();
433 let llval = match op {
434 mir::UnOp::Not => bx.not(lloperand),
435 mir::UnOp::Neg => if is_float {
442 val: OperandValue::Immediate(llval),
443 layout: operand.layout,
447 mir::Rvalue::Discriminant(ref place) => {
448 let discr_ty = rvalue.ty(&*self.mir, bx.tcx());
449 let discr = self.codegen_place(&mut bx, &place.as_ref())
450 .codegen_get_discr(&mut bx, discr_ty);
452 val: OperandValue::Immediate(discr),
453 layout: self.cx.layout_of(discr_ty)
457 mir::Rvalue::NullaryOp(mir::NullOp::SizeOf, ty) => {
458 assert!(bx.cx().type_is_sized(ty));
459 let val = bx.cx().const_usize(bx.cx().layout_of(ty).size.bytes());
460 let tcx = self.cx.tcx();
462 val: OperandValue::Immediate(val),
463 layout: self.cx.layout_of(tcx.types.usize),
467 mir::Rvalue::NullaryOp(mir::NullOp::Box, content_ty) => {
468 let content_ty = self.monomorphize(&content_ty);
469 let content_layout = bx.cx().layout_of(content_ty);
470 let llsize = bx.cx().const_usize(content_layout.size.bytes());
471 let llalign = bx.cx().const_usize(content_layout.align.abi.bytes());
472 let box_layout = bx.cx().layout_of(bx.tcx().mk_box(content_ty));
473 let llty_ptr = bx.cx().backend_type(box_layout);
476 let def_id = match bx.tcx().lang_items().require(ExchangeMallocFnLangItem) {
479 bx.cx().sess().fatal(&format!("allocation of `{}` {}", box_layout.ty, s));
482 let instance = ty::Instance::mono(bx.tcx(), def_id);
483 let r = bx.cx().get_fn(instance);
484 let call = bx.call(r, &[llsize, llalign], None);
485 let val = bx.pointercast(call, llty_ptr);
487 let operand = OperandRef {
488 val: OperandValue::Immediate(val),
493 mir::Rvalue::Use(ref operand) => {
494 let operand = self.codegen_operand(&mut bx, operand);
497 mir::Rvalue::Repeat(..) |
498 mir::Rvalue::Aggregate(..) => {
499 // According to `rvalue_creates_operand`, only ZST
500 // aggregate rvalues are allowed to be operands.
501 let ty = rvalue.ty(self.mir, self.cx.tcx());
502 let operand = OperandRef::new_zst(
504 self.cx.layout_of(self.monomorphize(&ty)),
511 fn evaluate_array_len(
514 place: &mir::Place<'tcx>,
516 // ZST are passed as operands and require special handling
517 // because codegen_place() panics if Local is operand.
519 base: mir::PlaceBase::Local(index),
522 if let LocalRef::Operand(Some(op)) = self.locals[index] {
523 if let ty::Array(_, n) = op.layout.ty.sty {
524 let n = n.unwrap_usize(bx.cx().tcx());
525 return bx.cx().const_usize(n);
529 // use common size calculation for non zero-sized types
530 let cg_value = self.codegen_place(bx, &place.as_ref());
531 cg_value.len(bx.cx())
534 pub fn codegen_scalar_binop(
542 let is_float = input_ty.is_floating_point();
543 let is_signed = input_ty.is_signed();
544 let is_unit = input_ty.is_unit();
546 mir::BinOp::Add => if is_float {
551 mir::BinOp::Sub => if is_float {
556 mir::BinOp::Mul => if is_float {
561 mir::BinOp::Div => if is_float {
563 } else if is_signed {
568 mir::BinOp::Rem => if is_float {
570 } else if is_signed {
575 mir::BinOp::BitOr => bx.or(lhs, rhs),
576 mir::BinOp::BitAnd => bx.and(lhs, rhs),
577 mir::BinOp::BitXor => bx.xor(lhs, rhs),
578 mir::BinOp::Offset => bx.inbounds_gep(lhs, &[rhs]),
579 mir::BinOp::Shl => common::build_unchecked_lshift(bx, lhs, rhs),
580 mir::BinOp::Shr => common::build_unchecked_rshift(bx, input_ty, lhs, rhs),
581 mir::BinOp::Ne | mir::BinOp::Lt | mir::BinOp::Gt |
582 mir::BinOp::Eq | mir::BinOp::Le | mir::BinOp::Ge => if is_unit {
583 bx.cx().const_bool(match op {
584 mir::BinOp::Ne | mir::BinOp::Lt | mir::BinOp::Gt => false,
585 mir::BinOp::Eq | mir::BinOp::Le | mir::BinOp::Ge => true,
590 base::bin_op_to_fcmp_predicate(op.to_hir_binop()),
595 base::bin_op_to_icmp_predicate(op.to_hir_binop(), is_signed),
602 pub fn codegen_fat_ptr_binop(
607 lhs_extra: Bx::Value,
609 rhs_extra: Bx::Value,
614 let lhs = bx.icmp(IntPredicate::IntEQ, lhs_addr, rhs_addr);
615 let rhs = bx.icmp(IntPredicate::IntEQ, lhs_extra, rhs_extra);
619 let lhs = bx.icmp(IntPredicate::IntNE, lhs_addr, rhs_addr);
620 let rhs = bx.icmp(IntPredicate::IntNE, lhs_extra, rhs_extra);
623 mir::BinOp::Le | mir::BinOp::Lt |
624 mir::BinOp::Ge | mir::BinOp::Gt => {
625 // a OP b ~ a.0 STRICT(OP) b.0 | (a.0 == b.0 && a.1 OP a.1)
626 let (op, strict_op) = match op {
627 mir::BinOp::Lt => (IntPredicate::IntULT, IntPredicate::IntULT),
628 mir::BinOp::Le => (IntPredicate::IntULE, IntPredicate::IntULT),
629 mir::BinOp::Gt => (IntPredicate::IntUGT, IntPredicate::IntUGT),
630 mir::BinOp::Ge => (IntPredicate::IntUGE, IntPredicate::IntUGT),
633 let lhs = bx.icmp(strict_op, lhs_addr, rhs_addr);
634 let and_lhs = bx.icmp(IntPredicate::IntEQ, lhs_addr, rhs_addr);
635 let and_rhs = bx.icmp(op, lhs_extra, rhs_extra);
636 let rhs = bx.and(and_lhs, and_rhs);
640 bug!("unexpected fat ptr binop");
645 pub fn codegen_scalar_checked_binop(
652 ) -> OperandValue<Bx::Value> {
653 // This case can currently arise only from functions marked
654 // with #[rustc_inherit_overflow_checks] and inlined from
655 // another crate (mostly core::num generic/#[inline] fns),
656 // while the current crate doesn't use overflow checks.
657 if !bx.cx().check_overflow() {
658 let val = self.codegen_scalar_binop(bx, op, lhs, rhs, input_ty);
659 return OperandValue::Pair(val, bx.cx().const_bool(false));
662 let (val, of) = match op {
663 // These are checked using intrinsics
664 mir::BinOp::Add | mir::BinOp::Sub | mir::BinOp::Mul => {
666 mir::BinOp::Add => OverflowOp::Add,
667 mir::BinOp::Sub => OverflowOp::Sub,
668 mir::BinOp::Mul => OverflowOp::Mul,
671 bx.checked_binop(oop, input_ty, lhs, rhs)
673 mir::BinOp::Shl | mir::BinOp::Shr => {
674 let lhs_llty = bx.cx().val_ty(lhs);
675 let rhs_llty = bx.cx().val_ty(rhs);
676 let invert_mask = common::shift_mask_val(bx, lhs_llty, rhs_llty, true);
677 let outer_bits = bx.and(rhs, invert_mask);
679 let of = bx.icmp(IntPredicate::IntNE, outer_bits, bx.cx().const_null(rhs_llty));
680 let val = self.codegen_scalar_binop(bx, op, lhs, rhs, input_ty);
685 bug!("Operator `{:?}` is not a checkable operator", op)
689 OperandValue::Pair(val, of)
693 impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
694 pub fn rvalue_creates_operand(&self, rvalue: &mir::Rvalue<'tcx>) -> bool {
696 mir::Rvalue::Ref(..) |
697 mir::Rvalue::Len(..) |
698 mir::Rvalue::Cast(..) | // (*)
699 mir::Rvalue::BinaryOp(..) |
700 mir::Rvalue::CheckedBinaryOp(..) |
701 mir::Rvalue::UnaryOp(..) |
702 mir::Rvalue::Discriminant(..) |
703 mir::Rvalue::NullaryOp(..) |
704 mir::Rvalue::Use(..) => // (*)
706 mir::Rvalue::Repeat(..) |
707 mir::Rvalue::Aggregate(..) => {
708 let ty = rvalue.ty(self.mir, self.cx.tcx());
709 let ty = self.monomorphize(&ty);
710 self.cx.layout_of(ty).is_zst()
714 // (*) this is only true if the type is suitable
718 fn cast_int_to_float<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
725 // Most integer types, even i128, fit into [-f32::MAX, f32::MAX] after rounding.
726 // It's only u128 -> f32 that can cause overflows (i.e., should yield infinity).
727 // LLVM's uitofp produces undef in those cases, so we manually check for that case.
728 let is_u128_to_f32 = !signed &&
729 bx.cx().int_width(int_ty) == 128 &&
730 bx.cx().float_width(float_ty) == 32;
732 // All inputs greater or equal to (f32::MAX + 0.5 ULP) are rounded to infinity,
733 // and for everything else LLVM's uitofp works just fine.
734 use rustc_apfloat::ieee::Single;
735 const MAX_F32_PLUS_HALF_ULP: u128 = ((1 << (Single::PRECISION + 1)) - 1)
736 << (Single::MAX_EXP - Single::PRECISION as i16);
737 let max = bx.cx().const_uint_big(int_ty, MAX_F32_PLUS_HALF_ULP);
738 let overflow = bx.icmp(IntPredicate::IntUGE, x, max);
739 let infinity_bits = bx.cx().const_u32(ieee::Single::INFINITY.to_bits() as u32);
740 let infinity = bx.bitcast(infinity_bits, float_ty);
741 let fp = bx.uitofp(x, float_ty);
742 bx.select(overflow, infinity, fp)
745 bx.sitofp(x, float_ty)
747 bx.uitofp(x, float_ty)
752 fn cast_float_to_int<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
759 let fptosui_result = if signed {
765 if !bx.cx().sess().opts.debugging_opts.saturating_float_casts {
766 return fptosui_result;
769 let int_width = bx.cx().int_width(int_ty);
770 let float_width = bx.cx().float_width(float_ty);
771 // LLVM's fpto[su]i returns undef when the input x is infinite, NaN, or does not fit into the
772 // destination integer type after rounding towards zero. This `undef` value can cause UB in
773 // safe code (see issue #10184), so we implement a saturating conversion on top of it:
774 // Semantically, the mathematical value of the input is rounded towards zero to the next
775 // mathematical integer, and then the result is clamped into the range of the destination
776 // integer type. Positive and negative infinity are mapped to the maximum and minimum value of
777 // the destination integer type. NaN is mapped to 0.
779 // Define f_min and f_max as the largest and smallest (finite) floats that are exactly equal to
780 // a value representable in int_ty.
781 // They are exactly equal to int_ty::{MIN,MAX} if float_ty has enough significand bits.
782 // Otherwise, int_ty::MAX must be rounded towards zero, as it is one less than a power of two.
783 // int_ty::MIN, however, is either zero or a negative power of two and is thus exactly
784 // representable. Note that this only works if float_ty's exponent range is sufficiently large.
785 // f16 or 256 bit integers would break this property. Right now the smallest float type is f32
786 // with exponents ranging up to 127, which is barely enough for i128::MIN = -2^127.
787 // On the other hand, f_max works even if int_ty::MAX is greater than float_ty::MAX. Because
788 // we're rounding towards zero, we just get float_ty::MAX (which is always an integer).
789 // This already happens today with u128::MAX = 2^128 - 1 > f32::MAX.
790 let int_max = |signed: bool, int_width: u64| -> u128 {
791 let shift_amount = 128 - int_width;
793 i128::MAX as u128 >> shift_amount
795 u128::MAX >> shift_amount
798 let int_min = |signed: bool, int_width: u64| -> i128 {
800 i128::MIN >> (128 - int_width)
806 let compute_clamp_bounds_single =
807 |signed: bool, int_width: u64| -> (u128, u128) {
808 let rounded_min = ieee::Single::from_i128_r(int_min(signed, int_width), Round::TowardZero);
809 assert_eq!(rounded_min.status, Status::OK);
810 let rounded_max = ieee::Single::from_u128_r(int_max(signed, int_width), Round::TowardZero);
811 assert!(rounded_max.value.is_finite());
812 (rounded_min.value.to_bits(), rounded_max.value.to_bits())
814 let compute_clamp_bounds_double =
815 |signed: bool, int_width: u64| -> (u128, u128) {
816 let rounded_min = ieee::Double::from_i128_r(int_min(signed, int_width), Round::TowardZero);
817 assert_eq!(rounded_min.status, Status::OK);
818 let rounded_max = ieee::Double::from_u128_r(int_max(signed, int_width), Round::TowardZero);
819 assert!(rounded_max.value.is_finite());
820 (rounded_min.value.to_bits(), rounded_max.value.to_bits())
823 let mut float_bits_to_llval = |bits| {
824 let bits_llval = match float_width {
825 32 => bx.cx().const_u32(bits as u32),
826 64 => bx.cx().const_u64(bits as u64),
827 n => bug!("unsupported float width {}", n),
829 bx.bitcast(bits_llval, float_ty)
831 let (f_min, f_max) = match float_width {
832 32 => compute_clamp_bounds_single(signed, int_width),
833 64 => compute_clamp_bounds_double(signed, int_width),
834 n => bug!("unsupported float width {}", n),
836 let f_min = float_bits_to_llval(f_min);
837 let f_max = float_bits_to_llval(f_max);
838 // To implement saturation, we perform the following steps:
840 // 1. Cast x to an integer with fpto[su]i. This may result in undef.
841 // 2. Compare x to f_min and f_max, and use the comparison results to select:
842 // a) int_ty::MIN if x < f_min or x is NaN
843 // b) int_ty::MAX if x > f_max
844 // c) the result of fpto[su]i otherwise
845 // 3. If x is NaN, return 0.0, otherwise return the result of step 2.
847 // This avoids resulting undef because values in range [f_min, f_max] by definition fit into the
848 // destination type. It creates an undef temporary, but *producing* undef is not UB. Our use of
849 // undef does not introduce any non-determinism either.
850 // More importantly, the above procedure correctly implements saturating conversion.
852 // If x is NaN, 0 is returned by definition.
853 // Otherwise, x is finite or infinite and thus can be compared with f_min and f_max.
854 // This yields three cases to consider:
855 // (1) if x in [f_min, f_max], the result of fpto[su]i is returned, which agrees with
856 // saturating conversion for inputs in that range.
857 // (2) if x > f_max, then x is larger than int_ty::MAX. This holds even if f_max is rounded
858 // (i.e., if f_max < int_ty::MAX) because in those cases, nextUp(f_max) is already larger
859 // than int_ty::MAX. Because x is larger than int_ty::MAX, the return value of int_ty::MAX
861 // (3) if x < f_min, then x is smaller than int_ty::MIN. As shown earlier, f_min exactly equals
862 // int_ty::MIN and therefore the return value of int_ty::MIN is correct.
865 // Step 1 was already performed above.
867 // Step 2: We use two comparisons and two selects, with %s1 being the result:
868 // %less_or_nan = fcmp ult %x, %f_min
869 // %greater = fcmp olt %x, %f_max
870 // %s0 = select %less_or_nan, int_ty::MIN, %fptosi_result
871 // %s1 = select %greater, int_ty::MAX, %s0
872 // Note that %less_or_nan uses an *unordered* comparison. This comparison is true if the
873 // operands are not comparable (i.e., if x is NaN). The unordered comparison ensures that s1
874 // becomes int_ty::MIN if x is NaN.
875 // Performance note: Unordered comparison can be lowered to a "flipped" comparison and a
876 // negation, and the negation can be merged into the select. Therefore, it not necessarily any
877 // more expensive than a ordered ("normal") comparison. Whether these optimizations will be
878 // performed is ultimately up to the backend, but at least x86 does perform them.
879 let less_or_nan = bx.fcmp(RealPredicate::RealULT, x, f_min);
880 let greater = bx.fcmp(RealPredicate::RealOGT, x, f_max);
881 let int_max = bx.cx().const_uint_big(int_ty, int_max(signed, int_width));
882 let int_min = bx.cx().const_uint_big(int_ty, int_min(signed, int_width) as u128);
883 let s0 = bx.select(less_or_nan, int_min, fptosui_result);
884 let s1 = bx.select(greater, int_max, s0);
886 // Step 3: NaN replacement.
887 // For unsigned types, the above step already yielded int_ty::MIN == 0 if x is NaN.
888 // Therefore we only need to execute this step for signed integer types.
890 // LLVM has no isNaN predicate, so we use (x == x) instead
891 let zero = bx.cx().const_uint(int_ty, 0);
892 let cmp = bx.fcmp(RealPredicate::RealOEQ, x, x);
893 bx.select(cmp, s1, zero)