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<'ll> 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: &llvm::Module) -> ValueIter<'_> {
  55     unsafe { ValueIter { cur: llvm::LLVMGetFirstGlobal(llmod), step: llvm::LLVMGetNextGlobal } }
  56 }
  57
  58 pub fn compile_codegen_unit(tcx: TyCtxt<'_>, cgu_name: Symbol) -> (ModuleCodegen<ModuleLlvm>, u64) {
  59     let start_time = Instant::now();
  60
  61     let dep_node = tcx.codegen_unit(cgu_name).codegen_dep_node(tcx);
  62     let (module, _) = tcx.dep_graph.with_task(
  63         dep_node,
  64         tcx,
  65         cgu_name,
  66         module_codegen,
  67         Some(dep_graph::hash_result),
  68     );
  69     let time_to_codegen = start_time.elapsed();
  70
  71     // We assume that the cost to run LLVM on a CGU is proportional to
  72     // the time we needed for codegenning it.
  73     let cost = time_to_codegen.as_nanos() as u64;
  74
  75     fn module_codegen(tcx: TyCtxt<'_>, cgu_name: Symbol) -> ModuleCodegen<ModuleLlvm> {
  76         let cgu = tcx.codegen_unit(cgu_name);
  77         let _prof_timer =
  78             tcx.prof.generic_activity_with_arg_recorder("codegen_module", |recorder| {
  79                 recorder.record_arg(cgu_name.to_string());
  80                 recorder.record_arg(cgu.size_estimate().to_string());
  81             });
  82         // Instantiate monomorphizations without filling out definitions yet...
  83         let llvm_module = ModuleLlvm::new(tcx, cgu_name.as_str());
  84         {
  85             let cx = CodegenCx::new(tcx, cgu, &llvm_module);
  86             let mono_items = cx.codegen_unit.items_in_deterministic_order(cx.tcx);
  87             for &(mono_item, (linkage, visibility)) in &mono_items {
  88                 mono_item.predefine::<Builder<'_, '_, '_>>(&cx, linkage, visibility);
  89             }
  90
  91             // ... and now that we have everything pre-defined, fill out those definitions.
  92             for &(mono_item, _) in &mono_items {
  93                 mono_item.define::<Builder<'_, '_, '_>>(&cx);
  94             }
  95
  96             // If this codegen unit contains the main function, also create the
  97             // wrapper here
  98             if let Some(entry) = maybe_create_entry_wrapper::<Builder<'_, '_, '_>>(&cx) {
  99                 let attrs = attributes::sanitize_attrs(&cx, SanitizerSet::empty());
 100                 attributes::apply_to_llfn(entry, llvm::AttributePlace::Function, &attrs);
 101             }
 102
 103             // Finalize code coverage by injecting the coverage map. Note, the coverage map will
 104             // also be added to the `llvm.compiler.used` variable, created next.
 105             if cx.sess().instrument_coverage() {
 106                 cx.coverageinfo_finalize();
 107             }
 108
 109             // Create the llvm.used and llvm.compiler.used variables.
 110             if !cx.used_statics().borrow().is_empty() {
 111                 cx.create_used_variable()
 112             }
 113             if !cx.compiler_used_statics().borrow().is_empty() {
 114                 cx.create_compiler_used_variable()
 115             }
 116
 117             // Run replace-all-uses-with for statics that need it. This must
 118             // happen after the llvm.used variables are created.
 119             for &(old_g, new_g) in cx.statics_to_rauw().borrow().iter() {
 120                 unsafe {
 121                     let bitcast = llvm::LLVMConstPointerCast(new_g, cx.val_ty(old_g));
 122                     llvm::LLVMReplaceAllUsesWith(old_g, bitcast);
 123                     llvm::LLVMDeleteGlobal(old_g);
 124                 }
 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 Some(sect) = attrs.link_section else { return };
 145     unsafe {
 146         let buf = SmallCStr::new(sect.as_str());
 147         llvm::LLVMSetSection(llval, buf.as_ptr());
 148     }
 149 }
 150
 151 pub fn linkage_to_llvm(linkage: Linkage) -> llvm::Linkage {
 152     match linkage {
 153         Linkage::External => llvm::Linkage::ExternalLinkage,
 154         Linkage::AvailableExternally => llvm::Linkage::AvailableExternallyLinkage,
 155         Linkage::LinkOnceAny => llvm::Linkage::LinkOnceAnyLinkage,
 156         Linkage::LinkOnceODR => llvm::Linkage::LinkOnceODRLinkage,
 157         Linkage::WeakAny => llvm::Linkage::WeakAnyLinkage,
 158         Linkage::WeakODR => llvm::Linkage::WeakODRLinkage,
 159         Linkage::Appending => llvm::Linkage::AppendingLinkage,
 160         Linkage::Internal => llvm::Linkage::InternalLinkage,
 161         Linkage::Private => llvm::Linkage::PrivateLinkage,
 162         Linkage::ExternalWeak => llvm::Linkage::ExternalWeakLinkage,
 163         Linkage::Common => llvm::Linkage::CommonLinkage,
 164     }
 165 }
 166
 167 pub fn visibility_to_llvm(linkage: Visibility) -> llvm::Visibility {
 168     match linkage {
 169         Visibility::Default => llvm::Visibility::Default,
 170         Visibility::Hidden => llvm::Visibility::Hidden,
 171         Visibility::Protected => llvm::Visibility::Protected,
 172     }
 173 }