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ef0719f36b
Implement -femit-local-var-lifetime which adds local (stack) variable lifetime annotation to LLVM IR, which enables sharing stack space for variables whose lifetimes do not overlap. Resolves issue #2227 This is not enabled by default yet, to prevent miscompilation due to bugs (should be enabled in future for optimization levels > 0, and when sanitizers are enabled).
97 lines
2.9 KiB
C++
97 lines
2.9 KiB
C++
//===-- gen/variable_lifetime.cpp - -----------------------------*- C++ -*-===//
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//
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// LDC – the LLVM D compiler
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//
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// This file is distributed under the BSD-style LDC license. See the LICENSE
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// file for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// Codegen for local variable lifetime: llvm.lifetime.start abd
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// llvm.lifetime.end.
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//
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//===----------------------------------------------------------------------===//
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#include "gen/variable_lifetime.h"
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#include "driver/cl_options.h"
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#include "gen/irstate.h"
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#include <vector>
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#include <utility>
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// TODO: make this option depend on -O and -fsanitize settings.
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static llvm::cl::opt<bool> fEmitLocalVarLifetime(
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"femit-local-var-lifetime",
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llvm::cl::desc(
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"Emit local variable lifetime, enabling more optimizations."),
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llvm::cl::Hidden, llvm::cl::ZeroOrMore);
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LocalVariableLifetimeAnnotator::LocalVariableLifetimeAnnotator(IRState &irs)
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: irs(irs) {
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allocaType =
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llvm::Type::getInt8Ty(irs.context())
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->getPointerTo(irs.module.getDataLayout().getAllocaAddrSpace());
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}
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void LocalVariableLifetimeAnnotator::pushScope() { scopes.emplace_back(); }
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void LocalVariableLifetimeAnnotator::addLocalVariable(llvm::Value *address,
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llvm::Value *size) {
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assert(address);
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assert(size);
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if (!fEmitLocalVarLifetime)
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return;
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if (scopes.empty())
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return;
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// Push to scopes
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scopes.back().variables.emplace_back(size, address);
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// Emit lifetime start
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address = irs.ir->CreateBitCast(address, allocaType);
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irs.CreateCallOrInvoke(getLLVMLifetimeStartFn(), {size, address}, "",
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true /*nothrow*/);
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}
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// Emits end-of-lifetime annotation for all variables in current scope.
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void LocalVariableLifetimeAnnotator::popScope() {
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if (scopes.empty())
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return;
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for (const auto &var : scopes.back().variables) {
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auto size = var.first;
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auto address = var.second;
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address = irs.ir->CreateBitCast(address, allocaType);
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assert(address);
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irs.CreateCallOrInvoke(getLLVMLifetimeEndFn(), {size, address}, "",
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true /*nothrow*/);
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}
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scopes.pop_back();
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}
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/// Lazily declare the @llvm.lifetime.start intrinsic.
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llvm::Function *LocalVariableLifetimeAnnotator::getLLVMLifetimeStartFn() {
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if (lifetimeStartFunction)
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return lifetimeStartFunction;
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lifetimeStartFunction = llvm::Intrinsic::getDeclaration(
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&irs.module, llvm::Intrinsic::lifetime_start, allocaType);
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assert(lifetimeStartFunction);
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return lifetimeStartFunction;
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}
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/// Lazily declare the @llvm.lifetime.end intrinsic.
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llvm::Function *LocalVariableLifetimeAnnotator::getLLVMLifetimeEndFn() {
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if (lifetimeEndFunction)
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return lifetimeEndFunction;
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lifetimeEndFunction = llvm::Intrinsic::getDeclaration(
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&irs.module, llvm::Intrinsic::lifetime_end, allocaType);
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assert(lifetimeEndFunction);
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return lifetimeEndFunction;
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}
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