compiler/rustc_codegen_llvm/src/base.rs - toolchain/rustc - Git at Google

 //! Codegen the MIR to the LLVM IR.
 //!
 //! Hopefully useful general knowledge about codegen:
 //!
 //! * There's no way to find out the [`Ty`] type of a [`Value`]. Doing so
 //!   would be "trying to get the eggs out of an omelette" (credit:
 //!   pcwalton). You can, instead, find out its [`llvm::Type`] by calling [`val_ty`],
 //!   but one [`llvm::Type`] corresponds to many [`Ty`]s; for instance, `tup(int, int,
 //!   int)` and `rec(x=int, y=int, z=int)` will have the same [`llvm::Type`].
 //!
 //! [`Ty`]: rustc_middle::ty::Ty
 //! [`val_ty`]: common::val_ty

 use super::ModuleLlvm;

 use crate::attributes;
 use crate::builder::Builder;
 use crate::common;
 use crate::context::CodegenCx;
 use crate::llvm;
 use crate::value::Value;

 use rustc_codegen_ssa::base::maybe_create_entry_wrapper;
 use rustc_codegen_ssa::mono_item::MonoItemExt;
 use rustc_codegen_ssa::traits::*;
 use rustc_codegen_ssa::{ModuleCodegen, ModuleKind};
 use rustc_data_structures::small_c_str::SmallCStr;
 use rustc_middle::dep_graph;
 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrs;
 use rustc_middle::middle::cstore::EncodedMetadata;
 use rustc_middle::middle::exported_symbols;
 use rustc_middle::mir::mono::{Linkage, Visibility};
 use rustc_middle::ty::TyCtxt;
 use rustc_session::config::DebugInfo;
 use rustc_span::symbol::Symbol;
 use rustc_target::spec::SanitizerSet;

 use std::ffi::CString;
 use std::time::Instant;

 pub fn write_compressed_metadata<'tcx>(
     tcx: TyCtxt<'tcx>,
     metadata: &EncodedMetadata,
     llvm_module: &mut ModuleLlvm,
 ) {
     use snap::write::FrameEncoder;
     use std::io::Write;

     // Historical note:
     //
     // When using link.exe it was seen that the section name `.note.rustc`
     // was getting shortened to `.note.ru`, and according to the PE and COFF
     // specification:
     //
     // > Executable images do not use a string table and do not support
     // > section names longer than 8 characters
     //
     // https://docs.microsoft.com/en-us/windows/win32/debug/pe-format
     //
     // As a result, we choose a slightly shorter name! As to why
     // `.note.rustc` works on MinGW, see
     // https://github.com/llvm/llvm-project/blob/llvmorg-12.0.0/lld/COFF/Writer.cpp#L1190-L1197
     let section_name = if tcx.sess.target.is_like_osx { "__DATA,.rustc" } else { ".rustc" };

     let (metadata_llcx, metadata_llmod) = (&*llvm_module.llcx, llvm_module.llmod());
     let mut compressed = rustc_metadata::METADATA_HEADER.to_vec();
     FrameEncoder::new(&mut compressed).write_all(&metadata.raw_data).unwrap();

     let llmeta = common::bytes_in_context(metadata_llcx, &compressed);
     let llconst = common::struct_in_context(metadata_llcx, &[llmeta], false);
     let name = exported_symbols::metadata_symbol_name(tcx);
     let buf = CString::new(name).unwrap();
     let llglobal =
         unsafe { llvm::LLVMAddGlobal(metadata_llmod, common::val_ty(llconst), buf.as_ptr()) };
     unsafe {
         llvm::LLVMSetInitializer(llglobal, llconst);
         let name = SmallCStr::new(section_name);
         llvm::LLVMSetSection(llglobal, name.as_ptr());

         // Also generate a .section directive to force no
         // flags, at least for ELF outputs, so that the
         // metadata doesn't get loaded into memory.
         let directive = format!(".section {}", section_name);
         llvm::LLVMSetModuleInlineAsm2(metadata_llmod, directive.as_ptr().cast(), directive.len())
     }
 }

 pub struct ValueIter<'ll> {
     cur: Option<&'ll Value>,
     step: unsafe extern "C" fn(&'ll Value) -> Option<&'ll Value>,
 }

 impl Iterator for ValueIter<'ll> {
     type Item = &'ll Value;

     fn next(&mut self) -> Option<&'ll Value> {
         let old = self.cur;
         if let Some(old) = old {
             self.cur = unsafe { (self.step)(old) };
         }
         old
     }
 }

 pub fn iter_globals(llmod: &'ll llvm::Module) -> ValueIter<'ll> {
     unsafe { ValueIter { cur: llvm::LLVMGetFirstGlobal(llmod), step: llvm::LLVMGetNextGlobal } }
 }

 pub fn compile_codegen_unit(
     tcx: TyCtxt<'tcx>,
     cgu_name: Symbol,
 ) -> (ModuleCodegen<ModuleLlvm>, u64) {
     let start_time = Instant::now();

     let dep_node = tcx.codegen_unit(cgu_name).codegen_dep_node(tcx);
     let (module, _) =
         tcx.dep_graph.with_task(dep_node, tcx, cgu_name, module_codegen, dep_graph::hash_result);
     let time_to_codegen = start_time.elapsed();

     // We assume that the cost to run LLVM on a CGU is proportional to
     // the time we needed for codegenning it.
     let cost = time_to_codegen.as_nanos() as u64;

     fn module_codegen(tcx: TyCtxt<'_>, cgu_name: Symbol) -> ModuleCodegen<ModuleLlvm> {
         let cgu = tcx.codegen_unit(cgu_name);
         let _prof_timer = tcx.prof.generic_activity_with_args(
             "codegen_module",
             &[cgu_name.to_string(), cgu.size_estimate().to_string()],
         );
         // Instantiate monomorphizations without filling out definitions yet...
         let llvm_module = ModuleLlvm::new(tcx, &cgu_name.as_str());
         {
             let cx = CodegenCx::new(tcx, cgu, &llvm_module);
             let mono_items = cx.codegen_unit.items_in_deterministic_order(cx.tcx);
             for &(mono_item, (linkage, visibility)) in &mono_items {
                 mono_item.predefine::<Builder<'_, '_, '_>>(&cx, linkage, visibility);
             }

             // ... and now that we have everything pre-defined, fill out those definitions.
             for &(mono_item, _) in &mono_items {
                 mono_item.define::<Builder<'_, '_, '_>>(&cx);
             }

             // If this codegen unit contains the main function, also create the
             // wrapper here
             if let Some(entry) = maybe_create_entry_wrapper::<Builder<'_, '_, '_>>(&cx) {
                 attributes::sanitize(&cx, SanitizerSet::empty(), entry);
             }

             // Run replace-all-uses-with for statics that need it
             for &(old_g, new_g) in cx.statics_to_rauw().borrow().iter() {
                 unsafe {
                     let bitcast = llvm::LLVMConstPointerCast(new_g, cx.val_ty(old_g));
                     llvm::LLVMReplaceAllUsesWith(old_g, bitcast);
                     llvm::LLVMDeleteGlobal(old_g);
                 }
             }

             // Finalize code coverage by injecting the coverage map. Note, the coverage map will
             // also be added to the `llvm.compiler.used` variable, created next.
             if cx.sess().instrument_coverage() {
                 cx.coverageinfo_finalize();
             }

             // Create the llvm.used and llvm.compiler.used variables.
             if !cx.used_statics().borrow().is_empty() {
                 cx.create_used_variable()
             }
             if !cx.compiler_used_statics().borrow().is_empty() {
                 cx.create_compiler_used_variable()
             }

             // Finalize debuginfo
             if cx.sess().opts.debuginfo != DebugInfo::None {
                 cx.debuginfo_finalize();
             }
         }

         ModuleCodegen {
             name: cgu_name.to_string(),
             module_llvm: llvm_module,
             kind: ModuleKind::Regular,
         }
     }

     (module, cost)
 }

 pub fn set_link_section(llval: &Value, attrs: &CodegenFnAttrs) {
     let sect = match attrs.link_section {
         Some(name) => name,
         None => return,
     };
     unsafe {
         let buf = SmallCStr::new(&sect.as_str());
         llvm::LLVMSetSection(llval, buf.as_ptr());
     }
 }

 pub fn linkage_to_llvm(linkage: Linkage) -> llvm::Linkage {
     match linkage {
         Linkage::External => llvm::Linkage::ExternalLinkage,
         Linkage::AvailableExternally => llvm::Linkage::AvailableExternallyLinkage,
         Linkage::LinkOnceAny => llvm::Linkage::LinkOnceAnyLinkage,
         Linkage::LinkOnceODR => llvm::Linkage::LinkOnceODRLinkage,
         Linkage::WeakAny => llvm::Linkage::WeakAnyLinkage,
         Linkage::WeakODR => llvm::Linkage::WeakODRLinkage,
         Linkage::Appending => llvm::Linkage::AppendingLinkage,
         Linkage::Internal => llvm::Linkage::InternalLinkage,
         Linkage::Private => llvm::Linkage::PrivateLinkage,
         Linkage::ExternalWeak => llvm::Linkage::ExternalWeakLinkage,
         Linkage::Common => llvm::Linkage::CommonLinkage,
     }
 }

 pub fn visibility_to_llvm(linkage: Visibility) -> llvm::Visibility {
     match linkage {
         Visibility::Default => llvm::Visibility::Default,
         Visibility::Hidden => llvm::Visibility::Hidden,
         Visibility::Protected => llvm::Visibility::Protected,
     }
 }
	//! Codegen the MIR to the LLVM IR.
	//!
	//! Hopefully useful general knowledge about codegen:
	//!
	//! * There's no way to find out the [`Ty`] type of a [`Value`]. Doing so
	//! would be "trying to get the eggs out of an omelette" (credit:
	//! pcwalton). You can, instead, find out its [`llvm::Type`] by calling [`val_ty`],
	//! but one [`llvm::Type`] corresponds to many [`Ty`]s; for instance, `tup(int, int,
	//! int)` and `rec(x=int, y=int, z=int)` will have the same [`llvm::Type`].
	//!
	//! [`Ty`]: rustc_middle::ty::Ty
	//! [`val_ty`]: common::val_ty

	use super::ModuleLlvm;

	use crate::attributes;
	use crate::builder::Builder;
	use crate::common;
	use crate::context::CodegenCx;
	use crate::llvm;
	use crate::value::Value;

	use rustc_codegen_ssa::base::maybe_create_entry_wrapper;
	use rustc_codegen_ssa::mono_item::MonoItemExt;
	use rustc_codegen_ssa::traits::*;
	use rustc_codegen_ssa::{ModuleCodegen, ModuleKind};
	use rustc_data_structures::small_c_str::SmallCStr;
	use rustc_middle::dep_graph;
	use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrs;
	use rustc_middle::middle::cstore::EncodedMetadata;
	use rustc_middle::middle::exported_symbols;
	use rustc_middle::mir::mono::{Linkage, Visibility};
	use rustc_middle::ty::TyCtxt;
	use rustc_session::config::DebugInfo;
	use rustc_span::symbol::Symbol;
	use rustc_target::spec::SanitizerSet;

	use std::ffi::CString;
	use std::time::Instant;

	pub fn write_compressed_metadata<'tcx>(
	tcx: TyCtxt<'tcx>,
	metadata: &EncodedMetadata,
	llvm_module: &mut ModuleLlvm,
	) {
	use snap::write::FrameEncoder;
	use std::io::Write;

	// Historical note:
	//
	// When using link.exe it was seen that the section name `.note.rustc`
	// was getting shortened to `.note.ru`, and according to the PE and COFF
	// specification:
	//
	// > Executable images do not use a string table and do not support
	// > section names longer than 8 characters
	//
	// https://docs.microsoft.com/en-us/windows/win32/debug/pe-format
	//
	// As a result, we choose a slightly shorter name! As to why
	// `.note.rustc` works on MinGW, see
	// https://github.com/llvm/llvm-project/blob/llvmorg-12.0.0/lld/COFF/Writer.cpp#L1190-L1197
	let section_name = if tcx.sess.target.is_like_osx { "__DATA,.rustc" } else { ".rustc" };

	let (metadata_llcx, metadata_llmod) = (&*llvm_module.llcx, llvm_module.llmod());
	let mut compressed = rustc_metadata::METADATA_HEADER.to_vec();
	FrameEncoder::new(&mut compressed).write_all(&metadata.raw_data).unwrap();

	let llmeta = common::bytes_in_context(metadata_llcx, &compressed);
	let llconst = common::struct_in_context(metadata_llcx, &[llmeta], false);
	let name = exported_symbols::metadata_symbol_name(tcx);
	let buf = CString::new(name).unwrap();
	let llglobal =
	unsafe { llvm::LLVMAddGlobal(metadata_llmod, common::val_ty(llconst), buf.as_ptr()) };
	unsafe {
	llvm::LLVMSetInitializer(llglobal, llconst);
	let name = SmallCStr::new(section_name);
	llvm::LLVMSetSection(llglobal, name.as_ptr());

	// Also generate a .section directive to force no
	// flags, at least for ELF outputs, so that the
	// metadata doesn't get loaded into memory.
	let directive = format!(".section {}", section_name);
	llvm::LLVMSetModuleInlineAsm2(metadata_llmod, directive.as_ptr().cast(), directive.len())
	}
	}

	pub struct ValueIter<'ll> {
	cur: Option<&'ll Value>,
	step: unsafe extern "C" fn(&'ll Value) -> Option<&'ll Value>,
	}

	impl Iterator for ValueIter<'ll> {
	type Item = &'ll Value;

	fn next(&mut self) -> Option<&'ll Value> {
	let old = self.cur;
	if let Some(old) = old {
	self.cur = unsafe { (self.step)(old) };
	}
	old
	}
	}

	pub fn iter_globals(llmod: &'ll llvm::Module) -> ValueIter<'ll> {
	unsafe { ValueIter { cur: llvm::LLVMGetFirstGlobal(llmod), step: llvm::LLVMGetNextGlobal } }
	}

	pub fn compile_codegen_unit(
	tcx: TyCtxt<'tcx>,
	cgu_name: Symbol,
	) -> (ModuleCodegen<ModuleLlvm>, u64) {
	let start_time = Instant::now();

	let dep_node = tcx.codegen_unit(cgu_name).codegen_dep_node(tcx);
	let (module, _) =
	tcx.dep_graph.with_task(dep_node, tcx, cgu_name, module_codegen, dep_graph::hash_result);
	let time_to_codegen = start_time.elapsed();

	// We assume that the cost to run LLVM on a CGU is proportional to
	// the time we needed for codegenning it.
	let cost = time_to_codegen.as_nanos() as u64;

	fn module_codegen(tcx: TyCtxt<'_>, cgu_name: Symbol) -> ModuleCodegen<ModuleLlvm> {
	let cgu = tcx.codegen_unit(cgu_name);
	let _prof_timer = tcx.prof.generic_activity_with_args(
	"codegen_module",
	&[cgu_name.to_string(), cgu.size_estimate().to_string()],
	);
	// Instantiate monomorphizations without filling out definitions yet...
	let llvm_module = ModuleLlvm::new(tcx, &cgu_name.as_str());
	{
	let cx = CodegenCx::new(tcx, cgu, &llvm_module);
	let mono_items = cx.codegen_unit.items_in_deterministic_order(cx.tcx);
	for &(mono_item, (linkage, visibility)) in &mono_items {
	mono_item.predefine::<Builder<'_, '_, '_>>(&cx, linkage, visibility);
	}

	// ... and now that we have everything pre-defined, fill out those definitions.
	for &(mono_item, _) in &mono_items {
	mono_item.define::<Builder<'_, '_, '_>>(&cx);
	}

	// If this codegen unit contains the main function, also create the
	// wrapper here
	if let Some(entry) = maybe_create_entry_wrapper::<Builder<'_, '_, '_>>(&cx) {
	attributes::sanitize(&cx, SanitizerSet::empty(), entry);
	}

	// Run replace-all-uses-with for statics that need it
	for &(old_g, new_g) in cx.statics_to_rauw().borrow().iter() {
	unsafe {
	let bitcast = llvm::LLVMConstPointerCast(new_g, cx.val_ty(old_g));
	llvm::LLVMReplaceAllUsesWith(old_g, bitcast);
	llvm::LLVMDeleteGlobal(old_g);
	}
	}

	// Finalize code coverage by injecting the coverage map. Note, the coverage map will
	// also be added to the `llvm.compiler.used` variable, created next.
	if cx.sess().instrument_coverage() {
	cx.coverageinfo_finalize();
	}

	// Create the llvm.used and llvm.compiler.used variables.
	if !cx.used_statics().borrow().is_empty() {
	cx.create_used_variable()
	}
	if !cx.compiler_used_statics().borrow().is_empty() {
	cx.create_compiler_used_variable()
	}

	// Finalize debuginfo
	if cx.sess().opts.debuginfo != DebugInfo::None {
	cx.debuginfo_finalize();
	}
	}

	ModuleCodegen {
	name: cgu_name.to_string(),
	module_llvm: llvm_module,
	kind: ModuleKind::Regular,
	}
	}

	(module, cost)
	}

	pub fn set_link_section(llval: &Value, attrs: &CodegenFnAttrs) {
	let sect = match attrs.link_section {
	Some(name) => name,
	None => return,
	};
	unsafe {
	let buf = SmallCStr::new(&sect.as_str());
	llvm::LLVMSetSection(llval, buf.as_ptr());
	}
	}

	pub fn linkage_to_llvm(linkage: Linkage) -> llvm::Linkage {
	match linkage {
	Linkage::External => llvm::Linkage::ExternalLinkage,
	Linkage::AvailableExternally => llvm::Linkage::AvailableExternallyLinkage,
	Linkage::LinkOnceAny => llvm::Linkage::LinkOnceAnyLinkage,
	Linkage::LinkOnceODR => llvm::Linkage::LinkOnceODRLinkage,
	Linkage::WeakAny => llvm::Linkage::WeakAnyLinkage,
	Linkage::WeakODR => llvm::Linkage::WeakODRLinkage,
	Linkage::Appending => llvm::Linkage::AppendingLinkage,
	Linkage::Internal => llvm::Linkage::InternalLinkage,
	Linkage::Private => llvm::Linkage::PrivateLinkage,
	Linkage::ExternalWeak => llvm::Linkage::ExternalWeakLinkage,
	Linkage::Common => llvm::Linkage::CommonLinkage,
	}
	}

	pub fn visibility_to_llvm(linkage: Visibility) -> llvm::Visibility {
	match linkage {
	Visibility::Default => llvm::Visibility::Default,
	Visibility::Hidden => llvm::Visibility::Hidden,
	Visibility::Protected => llvm::Visibility::Protected,
	}
	}