UpdateCompilerUsed.cpp
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//==-LTOInternalize.cpp - LLVM Link Time Optimizer Internalization Utility -==//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file defines a helper to run the internalization part of LTO.
//
//===----------------------------------------------------------------------===//
#include "llvm/LTO/legacy/UpdateCompilerUsed.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/CodeGen/TargetLowering.h"
#include "llvm/CodeGen/TargetSubtargetInfo.h"
#include "llvm/IR/LegacyPassManager.h"
#include "llvm/IR/Mangler.h"
#include "llvm/Transforms/Utils/ModuleUtils.h"
using namespace llvm;
namespace {
// Helper class that collects AsmUsed and user supplied libcalls.
class PreserveLibCallsAndAsmUsed {
public:
PreserveLibCallsAndAsmUsed(const StringSet<> &AsmUndefinedRefs,
const TargetMachine &TM,
std::vector<GlobalValue *> &LLVMUsed)
: AsmUndefinedRefs(AsmUndefinedRefs), TM(TM), LLVMUsed(LLVMUsed) {}
void findInModule(Module &TheModule) {
initializeLibCalls(TheModule);
for (Function &F : TheModule)
findLibCallsAndAsm(F);
for (GlobalVariable &GV : TheModule.globals())
findLibCallsAndAsm(GV);
for (GlobalAlias &GA : TheModule.aliases())
findLibCallsAndAsm(GA);
}
private:
// Inputs
const StringSet<> &AsmUndefinedRefs;
const TargetMachine &TM;
// Temps
llvm::Mangler Mangler;
StringSet<> Libcalls;
// Output
std::vector<GlobalValue *> &LLVMUsed;
// Collect names of runtime library functions. User-defined functions with the
// same names are added to llvm.compiler.used to prevent them from being
// deleted by optimizations.
void initializeLibCalls(const Module &TheModule) {
TargetLibraryInfoImpl TLII(Triple(TM.getTargetTriple()));
TargetLibraryInfo TLI(TLII);
// TargetLibraryInfo has info on C runtime library calls on the current
// target.
for (unsigned I = 0, E = static_cast<unsigned>(LibFunc::NumLibFuncs);
I != E; ++I) {
LibFunc F = static_cast<LibFunc>(I);
if (TLI.has(F))
Libcalls.insert(TLI.getName(F));
}
SmallPtrSet<const TargetLowering *, 1> TLSet;
for (const Function &F : TheModule) {
const TargetLowering *Lowering =
TM.getSubtargetImpl(F)->getTargetLowering();
if (Lowering && TLSet.insert(Lowering).second)
// TargetLowering has info on library calls that CodeGen expects to be
// available, both from the C runtime and compiler-rt.
for (unsigned I = 0, E = static_cast<unsigned>(RTLIB::UNKNOWN_LIBCALL);
I != E; ++I)
if (const char *Name =
Lowering->getLibcallName(static_cast<RTLIB::Libcall>(I)))
Libcalls.insert(Name);
}
}
void findLibCallsAndAsm(GlobalValue &GV) {
// There are no restrictions to apply to declarations.
if (GV.isDeclaration())
return;
// There is nothing more restrictive than private linkage.
if (GV.hasPrivateLinkage())
return;
// Conservatively append user-supplied runtime library functions (supplied
// either directly, or via a function alias) to llvm.compiler.used. These
// could be internalized and deleted by optimizations like -globalopt,
// causing problems when later optimizations add new library calls (e.g.,
// llvm.memset => memset and printf => puts).
// Leave it to the linker to remove any dead code (e.g. with -dead_strip).
GlobalValue *FuncAliasee = nullptr;
if (isa<GlobalAlias>(GV)) {
auto *A = cast<GlobalAlias>(&GV);
FuncAliasee = dyn_cast<Function>(A->getAliasee());
}
if ((isa<Function>(GV) || FuncAliasee) && Libcalls.count(GV.getName())) {
LLVMUsed.push_back(&GV);
return;
}
SmallString<64> Buffer;
TM.getNameWithPrefix(Buffer, &GV, Mangler);
if (AsmUndefinedRefs.count(Buffer))
LLVMUsed.push_back(&GV);
}
};
} // namespace anonymous
void llvm::updateCompilerUsed(Module &TheModule, const TargetMachine &TM,
const StringSet<> &AsmUndefinedRefs) {
std::vector<GlobalValue *> UsedValues;
PreserveLibCallsAndAsmUsed(AsmUndefinedRefs, TM, UsedValues)
.findInModule(TheModule);
if (UsedValues.empty())
return;
appendToCompilerUsed(TheModule, UsedValues);
}