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 rustc_codegen_ssa::base::maybe_create_entry_wrapper;
  23 use rustc_codegen_ssa::mono_item::MonoItemExt;
  24 use rustc_codegen_ssa::traits::*;
  25 use rustc_codegen_ssa::{ModuleCodegen, ModuleKind};
  26 use rustc_data_structures::small_c_str::SmallCStr;
  27 use rustc_middle::dep_graph;
  28 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrs;
  29 use rustc_middle::mir::mono::{Linkage, Visibility};
  30 use rustc_middle::ty::TyCtxt;
  31 use rustc_session::config::DebugInfo;
  32 use rustc_span::symbol::Symbol;
  33 use rustc_target::spec::SanitizerSet;
  34
  35 use std::time::Instant;
  36
  37 pub struct ValueIter<'ll> {
  38     cur: Option<&'ll Value>,
  39     step: unsafe extern "C" fn(&'ll Value) -> Option<&'ll Value>,
  40 }
  41
  42 impl Iterator for ValueIter<'ll> {
  43     type Item = &'ll Value;
  44
  45     fn next(&mut self) -> Option<&'ll Value> {
  46         let old = self.cur;
  47         if let Some(old) = old {
  48             self.cur = unsafe { (self.step)(old) };
  49         }
  50         old
  51     }
  52 }
  53
  54 pub fn iter_globals(llmod: &'ll llvm::Module) -> ValueIter<'ll> {
  55     unsafe { ValueIter { cur: llvm::LLVMGetFirstGlobal(llmod), step: llvm::LLVMGetNextGlobal } }
  56 }
  57
  58 pub fn compile_codegen_unit(
  59     tcx: TyCtxt<'tcx>,
  60     cgu_name: Symbol,
  61 ) -> (ModuleCodegen<ModuleLlvm>, u64) {
  62     let start_time = Instant::now();
  63
  64     let dep_node = tcx.codegen_unit(cgu_name).codegen_dep_node(tcx);
  65     let (module, _) = tcx.dep_graph.with_task(
  66         dep_node,
  67         tcx,
  68         cgu_name,
  69         module_codegen,
  70         Some(dep_graph::hash_result),
  71     );
  72     let time_to_codegen = start_time.elapsed();
  73
  74     // We assume that the cost to run LLVM on a CGU is proportional to
  75     // the time we needed for codegenning it.
  76     let cost = time_to_codegen.as_nanos() as u64;
  77
  78     fn module_codegen(tcx: TyCtxt<'_>, cgu_name: Symbol) -> ModuleCodegen<ModuleLlvm> {
  79         let cgu = tcx.codegen_unit(cgu_name);
  80         let _prof_timer = tcx.prof.generic_activity_with_args(
  81             "codegen_module",
  82             &[cgu_name.to_string(), 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                 attributes::sanitize(&cx, SanitizerSet::empty(), entry);
 102             }
 103
 104             // Run replace-all-uses-with for statics that need it
 105             for &(old_g, new_g) in cx.statics_to_rauw().borrow().iter() {
 106                 unsafe {
 107                     let bitcast = llvm::LLVMConstPointerCast(new_g, cx.val_ty(old_g));
 108                     llvm::LLVMReplaceAllUsesWith(old_g, bitcast);
 109                     llvm::LLVMDeleteGlobal(old_g);
 110                 }
 111             }
 112
 113             // Finalize code coverage by injecting the coverage map. Note, the coverage map will
 114             // also be added to the `llvm.compiler.used` variable, created next.
 115             if cx.sess().instrument_coverage() {
 116                 cx.coverageinfo_finalize();
 117             }
 118
 119             // Create the llvm.used and llvm.compiler.used variables.
 120             if !cx.used_statics().borrow().is_empty() {
 121                 cx.create_used_variable()
 122             }
 123             if !cx.compiler_used_statics().borrow().is_empty() {
 124                 cx.create_compiler_used_variable()
 125             }
 126
 127             // Finalize debuginfo
 128             if cx.sess().opts.debuginfo != DebugInfo::None {
 129                 cx.debuginfo_finalize();
 130             }
 131         }
 132
 133         ModuleCodegen {
 134             name: cgu_name.to_string(),
 135             module_llvm: llvm_module,
 136             kind: ModuleKind::Regular,
 137         }
 138     }
 139
 140     (module, cost)
 141 }
 142
 143 pub fn set_link_section(llval: &Value, attrs: &CodegenFnAttrs) {
 144     let sect = match attrs.link_section {
 145         Some(name) => name,
 146         None => return,
 147     };
 148     unsafe {
 149         let buf = SmallCStr::new(&sect.as_str());
 150         llvm::LLVMSetSection(llval, buf.as_ptr());
 151     }
 152 }
 153
 154 pub fn linkage_to_llvm(linkage: Linkage) -> llvm::Linkage {
 155     match linkage {
 156         Linkage::External => llvm::Linkage::ExternalLinkage,
 157         Linkage::AvailableExternally => llvm::Linkage::AvailableExternallyLinkage,
 158         Linkage::LinkOnceAny => llvm::Linkage::LinkOnceAnyLinkage,
 159         Linkage::LinkOnceODR => llvm::Linkage::LinkOnceODRLinkage,
 160         Linkage::WeakAny => llvm::Linkage::WeakAnyLinkage,
 161         Linkage::WeakODR => llvm::Linkage::WeakODRLinkage,
 162         Linkage::Appending => llvm::Linkage::AppendingLinkage,
 163         Linkage::Internal => llvm::Linkage::InternalLinkage,
 164         Linkage::Private => llvm::Linkage::PrivateLinkage,
 165         Linkage::ExternalWeak => llvm::Linkage::ExternalWeakLinkage,
 166         Linkage::Common => llvm::Linkage::CommonLinkage,
 167     }
 168 }
 169
 170 pub fn visibility_to_llvm(linkage: Visibility) -> llvm::Visibility {
 171     match linkage {
 172         Visibility::Default => llvm::Visibility::Default,
 173         Visibility::Hidden => llvm::Visibility::Hidden,
 174         Visibility::Protected => llvm::Visibility::Protected,
 175     }
 176 }