compiler/rustc_codegen_llvm/src/base.rs

   1 //! Codegen the MIR to the LLVM IR.
   2 //!
   3 //! Hopefully useful general knowledge about codegen:
   4 //!
   5 //! * There's no way to find out the [`Ty`] type of a [`Value`]. Doing so
   6 //!   would be "trying to get the eggs out of an omelette" (credit:
   7 //!   pcwalton). You can, instead, find out its [`llvm::Type`] by calling [`val_ty`],
   8 //!   but one [`llvm::Type`] corresponds to many [`Ty`]s; for instance, `tup(int, int,
   9 //!   int)` and `rec(x=int, y=int, z=int)` will have the same [`llvm::Type`].
  10 //!
  11 //! [`Ty`]: rustc_middle::ty::Ty
  12 //! [`val_ty`]: crate::common::val_ty
  13
  14 use super::ModuleLlvm;
  15
  16 use crate::attributes;
  17 use crate::builder::Builder;
  18 use crate::context::CodegenCx;
  19 use crate::llvm;
  20 use crate::value::Value;
  21
  22 use cstr::cstr;
  23
  24 use rustc_codegen_ssa::base::maybe_create_entry_wrapper;
  25 use rustc_codegen_ssa::mono_item::MonoItemExt;
  26 use rustc_codegen_ssa::traits::*;
  27 use rustc_codegen_ssa::{ModuleCodegen, ModuleKind};
  28 use rustc_data_structures::small_c_str::SmallCStr;
  29 use rustc_middle::dep_graph;
  30 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrs;
  31 use rustc_middle::mir::mono::{Linkage, Visibility};
  32 use rustc_middle::ty::TyCtxt;
  33 use rustc_session::config::DebugInfo;
  34 use rustc_span::symbol::Symbol;
  35 use rustc_target::spec::SanitizerSet;
  36
  37 use std::time::Instant;
  38
  39 pub struct ValueIter<'ll> {
  40     cur: Option<&'ll Value>,
  41     step: unsafe extern "C" fn(&'ll Value) -> Option<&'ll Value>,
  42 }
  43
  44 impl<'ll> Iterator for ValueIter<'ll> {
  45     type Item = &'ll Value;
  46
  47     fn next(&mut self) -> Option<&'ll Value> {
  48         let old = self.cur;
  49         if let Some(old) = old {
  50             self.cur = unsafe { (self.step)(old) };
  51         }
  52         old
  53     }
  54 }
  55
  56 pub fn iter_globals(llmod: &llvm::Module) -> ValueIter<'_> {
  57     unsafe { ValueIter { cur: llvm::LLVMGetFirstGlobal(llmod), step: llvm::LLVMGetNextGlobal } }
  58 }
  59
  60 pub fn compile_codegen_unit(tcx: TyCtxt<'_>, cgu_name: Symbol) -> (ModuleCodegen<ModuleLlvm>, u64) {
  61     let start_time = Instant::now();
  62
  63     let dep_node = tcx.codegen_unit(cgu_name).codegen_dep_node(tcx);
  64     let (module, _) = tcx.dep_graph.with_task(
  65         dep_node,
  66         tcx,
  67         cgu_name,
  68         module_codegen,
  69         Some(dep_graph::hash_result),
  70     );
  71     let time_to_codegen = start_time.elapsed();
  72
  73     // We assume that the cost to run LLVM on a CGU is proportional to
  74     // the time we needed for codegenning it.
  75     let cost = time_to_codegen.as_nanos() as u64;
  76
  77     fn module_codegen(tcx: TyCtxt<'_>, cgu_name: Symbol) -> ModuleCodegen<ModuleLlvm> {
  78         let cgu = tcx.codegen_unit(cgu_name);
  79         let _prof_timer =
  80             tcx.prof.generic_activity_with_arg_recorder("codegen_module", |recorder| {
  81                 recorder.record_arg(cgu_name.to_string());
  82                 recorder.record_arg(cgu.size_estimate().to_string());
  83             });
  84         // Instantiate monomorphizations without filling out definitions yet...
  85         let llvm_module = ModuleLlvm::new(tcx, cgu_name.as_str());
  86         {
  87             let cx = CodegenCx::new(tcx, cgu, &llvm_module);
  88             let mono_items = cx.codegen_unit.items_in_deterministic_order(cx.tcx);
  89             for &(mono_item, (linkage, visibility)) in &mono_items {
  90                 mono_item.predefine::<Builder<'_, '_, '_>>(&cx, linkage, visibility);
  91             }
  92
  93             // ... and now that we have everything pre-defined, fill out those definitions.
  94             for &(mono_item, _) in &mono_items {
  95                 mono_item.define::<Builder<'_, '_, '_>>(&cx);
  96             }
  97
  98             // If this codegen unit contains the main function, also create the
  99             // wrapper here
 100             if let Some(entry) = maybe_create_entry_wrapper::<Builder<'_, '_, '_>>(&cx) {
 101                 let attrs = attributes::sanitize_attrs(&cx, SanitizerSet::empty());
 102                 attributes::apply_to_llfn(entry, llvm::AttributePlace::Function, &attrs);
 103             }
 104
 105             // Finalize code coverage by injecting the coverage map. Note, the coverage map will
 106             // also be added to the `llvm.compiler.used` variable, created next.
 107             if cx.sess().instrument_coverage() {
 108                 cx.coverageinfo_finalize();
 109             }
 110
 111             // Create the llvm.used and llvm.compiler.used variables.
 112             if !cx.used_statics.borrow().is_empty() {
 113                 cx.create_used_variable_impl(cstr!("llvm.used"), &*cx.used_statics.borrow());
 114             }
 115             if !cx.compiler_used_statics.borrow().is_empty() {
 116                 cx.create_used_variable_impl(
 117                     cstr!("llvm.compiler.used"),
 118                     &*cx.compiler_used_statics.borrow(),
 119                 );
 120             }
 121
 122             // Run replace-all-uses-with for statics that need it. This must
 123             // happen after the llvm.used variables are created.
 124             for &(old_g, new_g) in cx.statics_to_rauw().borrow().iter() {
 125                 unsafe {
 126                     let bitcast = llvm::LLVMConstPointerCast(new_g, cx.val_ty(old_g));
 127                     llvm::LLVMReplaceAllUsesWith(old_g, bitcast);
 128                     llvm::LLVMDeleteGlobal(old_g);
 129                 }
 130             }
 131
 132             // Finalize debuginfo
 133             if cx.sess().opts.debuginfo != DebugInfo::None {
 134                 cx.debuginfo_finalize();
 135             }
 136         }
 137
 138         ModuleCodegen {
 139             name: cgu_name.to_string(),
 140             module_llvm: llvm_module,
 141             kind: ModuleKind::Regular,
 142         }
 143     }
 144
 145     (module, cost)
 146 }
 147
 148 pub fn set_link_section(llval: &Value, attrs: &CodegenFnAttrs) {
 149     let Some(sect) = attrs.link_section else { return };
 150     unsafe {
 151         let buf = SmallCStr::new(sect.as_str());
 152         llvm::LLVMSetSection(llval, buf.as_ptr());
 153     }
 154 }
 155
 156 pub fn linkage_to_llvm(linkage: Linkage) -> llvm::Linkage {
 157     match linkage {
 158         Linkage::External => llvm::Linkage::ExternalLinkage,
 159         Linkage::AvailableExternally => llvm::Linkage::AvailableExternallyLinkage,
 160         Linkage::LinkOnceAny => llvm::Linkage::LinkOnceAnyLinkage,
 161         Linkage::LinkOnceODR => llvm::Linkage::LinkOnceODRLinkage,
 162         Linkage::WeakAny => llvm::Linkage::WeakAnyLinkage,
 163         Linkage::WeakODR => llvm::Linkage::WeakODRLinkage,
 164         Linkage::Appending => llvm::Linkage::AppendingLinkage,
 165         Linkage::Internal => llvm::Linkage::InternalLinkage,
 166         Linkage::Private => llvm::Linkage::PrivateLinkage,
 167         Linkage::ExternalWeak => llvm::Linkage::ExternalWeakLinkage,
 168         Linkage::Common => llvm::Linkage::CommonLinkage,
 169     }
 170 }
 171
 172 pub fn visibility_to_llvm(linkage: Visibility) -> llvm::Visibility {
 173     match linkage {
 174         Visibility::Default => llvm::Visibility::Default,
 175         Visibility::Hidden => llvm::Visibility::Hidden,
 176         Visibility::Protected => llvm::Visibility::Protected,
 177     }
 178 }