src/librustc_codegen_llvm/base.rs

   1 //! Codegen the completed AST to the LLVM IR.
   2 //!
   3 //! Some functions here, such as codegen_block and codegen_expr, return a value --
   4 //! the result of the codegen to LLVM -- while others, such as codegen_fn
   5 //! and mono_item, are called only for the side effect of adding a
   6 //! particular definition to the LLVM IR output we're producing.
   7 //!
   8 //! Hopefully useful general knowledge about codegen:
   9 //!
  10 //! * There's no way to find out the `Ty` type of a Value. Doing so
  11 //!   would be "trying to get the eggs out of an omelette" (credit:
  12 //!   pcwalton). You can, instead, find out its `llvm::Type` by calling `val_ty`,
  13 //!   but one `llvm::Type` corresponds to many `Ty`s; for instance, `tup(int, int,
  14 //!   int)` and `rec(x=int, y=int, z=int)` will have the same `llvm::Type`.
  15
  16 use super::ModuleLlvm;
  17
  18 use crate::attributes;
  19 use crate::builder::Builder;
  20 use crate::common;
  21 use crate::context::CodegenCx;
  22 use crate::llvm;
  23 use crate::metadata;
  24 use crate::value::Value;
  25
  26 use rustc_codegen_ssa::base::maybe_create_entry_wrapper;
  27 use rustc_codegen_ssa::mono_item::MonoItemExt;
  28 use rustc_codegen_ssa::traits::*;
  29 use rustc_codegen_ssa::{ModuleCodegen, ModuleKind};
  30 use rustc_data_structures::small_c_str::SmallCStr;
  31 use rustc_middle::dep_graph;
  32 use rustc_middle::middle::codegen_fn_attrs::{CodegenFnAttrFlags, CodegenFnAttrs};
  33 use rustc_middle::middle::cstore::EncodedMetadata;
  34 use rustc_middle::middle::exported_symbols;
  35 use rustc_middle::mir::mono::{Linkage, Visibility};
  36 use rustc_middle::ty::TyCtxt;
  37 use rustc_session::config::DebugInfo;
  38 use rustc_span::symbol::Symbol;
  39
  40 use std::ffi::CString;
  41 use std::time::Instant;
  42
  43 pub fn write_compressed_metadata<'tcx>(
  44     tcx: TyCtxt<'tcx>,
  45     metadata: &EncodedMetadata,
  46     llvm_module: &mut ModuleLlvm,
  47 ) {
  48     use flate2::write::DeflateEncoder;
  49     use flate2::Compression;
  50     use std::io::Write;
  51
  52     let (metadata_llcx, metadata_llmod) = (&*llvm_module.llcx, llvm_module.llmod());
  53     let mut compressed = tcx.metadata_encoding_version();
  54     DeflateEncoder::new(&mut compressed, Compression::fast())
  55         .write_all(&metadata.raw_data)
  56         .unwrap();
  57
  58     let llmeta = common::bytes_in_context(metadata_llcx, &compressed);
  59     let llconst = common::struct_in_context(metadata_llcx, &[llmeta], false);
  60     let name = exported_symbols::metadata_symbol_name(tcx);
  61     let buf = CString::new(name).unwrap();
  62     let llglobal =
  63         unsafe { llvm::LLVMAddGlobal(metadata_llmod, common::val_ty(llconst), buf.as_ptr()) };
  64     unsafe {
  65         llvm::LLVMSetInitializer(llglobal, llconst);
  66         let section_name = metadata::metadata_section_name(&tcx.sess.target.target);
  67         let name = SmallCStr::new(section_name);
  68         llvm::LLVMSetSection(llglobal, name.as_ptr());
  69
  70         // Also generate a .section directive to force no
  71         // flags, at least for ELF outputs, so that the
  72         // metadata doesn't get loaded into memory.
  73         let directive = format!(".section {}", section_name);
  74         llvm::LLVMSetModuleInlineAsm2(metadata_llmod, directive.as_ptr().cast(), directive.len())
  75     }
  76 }
  77
  78 pub struct ValueIter<'ll> {
  79     cur: Option<&'ll Value>,
  80     step: unsafe extern "C" fn(&'ll Value) -> Option<&'ll Value>,
  81 }
  82
  83 impl Iterator for ValueIter<'ll> {
  84     type Item = &'ll Value;
  85
  86     fn next(&mut self) -> Option<&'ll Value> {
  87         let old = self.cur;
  88         if let Some(old) = old {
  89             self.cur = unsafe { (self.step)(old) };
  90         }
  91         old
  92     }
  93 }
  94
  95 pub fn iter_globals(llmod: &'ll llvm::Module) -> ValueIter<'ll> {
  96     unsafe { ValueIter { cur: llvm::LLVMGetFirstGlobal(llmod), step: llvm::LLVMGetNextGlobal } }
  97 }
  98
  99 pub fn compile_codegen_unit(
 100     tcx: TyCtxt<'tcx>,
 101     cgu_name: Symbol,
 102 ) -> (ModuleCodegen<ModuleLlvm>, u64) {
 103     let prof_timer = tcx.prof.generic_activity("codegen_module");
 104     let start_time = Instant::now();
 105
 106     let dep_node = tcx.codegen_unit(cgu_name).codegen_dep_node(tcx);
 107     let (module, _) =
 108         tcx.dep_graph.with_task(dep_node, tcx, cgu_name, module_codegen, dep_graph::hash_result);
 109     let time_to_codegen = start_time.elapsed();
 110     drop(prof_timer);
 111
 112     // We assume that the cost to run LLVM on a CGU is proportional to
 113     // the time we needed for codegenning it.
 114     let cost = time_to_codegen.as_secs() * 1_000_000_000 + time_to_codegen.subsec_nanos() as u64;
 115
 116     fn module_codegen(tcx: TyCtxt<'_>, cgu_name: Symbol) -> ModuleCodegen<ModuleLlvm> {
 117         let cgu = tcx.codegen_unit(cgu_name);
 118         // Instantiate monomorphizations without filling out definitions yet...
 119         let llvm_module = ModuleLlvm::new(tcx, &cgu_name.as_str());
 120         {
 121             let cx = CodegenCx::new(tcx, cgu, &llvm_module);
 122             let mono_items = cx.codegen_unit.items_in_deterministic_order(cx.tcx);
 123             for &(mono_item, (linkage, visibility)) in &mono_items {
 124                 mono_item.predefine::<Builder<'_, '_, '_>>(&cx, linkage, visibility);
 125             }
 126
 127             // ... and now that we have everything pre-defined, fill out those definitions.
 128             for &(mono_item, _) in &mono_items {
 129                 mono_item.define::<Builder<'_, '_, '_>>(&cx);
 130             }
 131
 132             // If this codegen unit contains the main function, also create the
 133             // wrapper here
 134             if let Some(entry) = maybe_create_entry_wrapper::<Builder<'_, '_, '_>>(&cx) {
 135                 attributes::sanitize(&cx, CodegenFnAttrFlags::empty(), entry);
 136             }
 137
 138             // Run replace-all-uses-with for statics that need it
 139             for &(old_g, new_g) in cx.statics_to_rauw().borrow().iter() {
 140                 unsafe {
 141                     let bitcast = llvm::LLVMConstPointerCast(new_g, cx.val_ty(old_g));
 142                     llvm::LLVMReplaceAllUsesWith(old_g, bitcast);
 143                     llvm::LLVMDeleteGlobal(old_g);
 144                 }
 145             }
 146
 147             // Create the llvm.used variable
 148             // This variable has type [N x i8*] and is stored in the llvm.metadata section
 149             if !cx.used_statics().borrow().is_empty() {
 150                 cx.create_used_variable()
 151             }
 152
 153             // Finalize debuginfo
 154             if cx.sess().opts.debuginfo != DebugInfo::None {
 155                 cx.debuginfo_finalize();
 156             }
 157         }
 158
 159         ModuleCodegen {
 160             name: cgu_name.to_string(),
 161             module_llvm: llvm_module,
 162             kind: ModuleKind::Regular,
 163         }
 164     }
 165
 166     (module, cost)
 167 }
 168
 169 pub fn set_link_section(llval: &Value, attrs: &CodegenFnAttrs) {
 170     let sect = match attrs.link_section {
 171         Some(name) => name,
 172         None => return,
 173     };
 174     unsafe {
 175         let buf = SmallCStr::new(&sect.as_str());
 176         llvm::LLVMSetSection(llval, buf.as_ptr());
 177     }
 178 }
 179
 180 pub fn linkage_to_llvm(linkage: Linkage) -> llvm::Linkage {
 181     match linkage {
 182         Linkage::External => llvm::Linkage::ExternalLinkage,
 183         Linkage::AvailableExternally => llvm::Linkage::AvailableExternallyLinkage,
 184         Linkage::LinkOnceAny => llvm::Linkage::LinkOnceAnyLinkage,
 185         Linkage::LinkOnceODR => llvm::Linkage::LinkOnceODRLinkage,
 186         Linkage::WeakAny => llvm::Linkage::WeakAnyLinkage,
 187         Linkage::WeakODR => llvm::Linkage::WeakODRLinkage,
 188         Linkage::Appending => llvm::Linkage::AppendingLinkage,
 189         Linkage::Internal => llvm::Linkage::InternalLinkage,
 190         Linkage::Private => llvm::Linkage::PrivateLinkage,
 191         Linkage::ExternalWeak => llvm::Linkage::ExternalWeakLinkage,
 192         Linkage::Common => llvm::Linkage::CommonLinkage,
 193     }
 194 }
 195
 196 pub fn visibility_to_llvm(linkage: Visibility) -> llvm::Visibility {
 197     match linkage {
 198         Visibility::Default => llvm::Visibility::Default,
 199         Visibility::Hidden => llvm::Visibility::Hidden,
 200         Visibility::Protected => llvm::Visibility::Protected,
 201     }
 202 }