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Protect user-supplied runtime library functions in LTO

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Add user-supplied C runtime and compiler-rt library functions to
llvm.compiler.used to protect them from premature optimization by
passes like -globalopt and -ipsccp.  Calls to (seemingly unused)
runtime library functions can be added by -instcombine and instruction
lowering.

Patch by Duncan Exon Smith, thanks!

Fixes <rdar://problem/14740087>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194514 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Justin Bogner
2013-11-12 21:44:01 +00:00
parent 59e648e3c8
commit dc6b4b4fc2
3 changed files with 76 additions and 3 deletions
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49
lib/LTO/LTOCodeGenerator.cpp
View File

@ -18,6 +18,7 @@
#include "llvm/Analysis/Passes.h"
#include "llvm/Analysis/Verifier.h"
#include "llvm/Bitcode/ReaderWriter.h"
#include "llvm/CodeGen/RuntimeLibcalls.h"
#include "llvm/Config/config.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DataLayout.h"
@ -40,6 +41,8 @@
#include "llvm/Support/TargetSelect.h"
#include "llvm/Support/ToolOutputFile.h"
#include "llvm/Support/system_error.h"
#include "llvm/Target/TargetLibraryInfo.h"
#include "llvm/Target/TargetLowering.h"
#include "llvm/Target/TargetOptions.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Target/Mangler.h"
@ -312,6 +315,7 @@ bool LTOCodeGenerator::determineTarget(std::string &errMsg) {
void LTOCodeGenerator::
applyRestriction(GlobalValue &GV,
const ArrayRef<StringRef> &Libcalls,
std::vector<const char*> &MustPreserveList,
SmallPtrSet<GlobalValue*, 8> &AsmUsed,
Mangler &Mangler) {
@ -324,6 +328,15 @@ applyRestriction(GlobalValue &GV,
MustPreserveList.push_back(GV.getName().data());
if (AsmUndefinedRefs.count(Buffer))
AsmUsed.insert(&GV);
// Conservatively append user-supplied runtime library functions 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).
if (isa<Function>(GV) &&
std::binary_search(Libcalls.begin(), Libcalls.end(), GV.getName()))
AsmUsed.insert(&GV);
}
static void findUsedValues(GlobalVariable *LLVMUsed,
@ -337,6 +350,33 @@ static void findUsedValues(GlobalVariable *LLVMUsed,
UsedValues.insert(GV);
}
static void accumulateAndSortLibcalls(std::vector<StringRef> &Libcalls,
const TargetLibraryInfo& TLI,
const TargetLowering *Lowering)
{
// 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::Func F = static_cast<LibFunc::Func>(I);
if (TLI.has(F))
Libcalls.push_back(TLI.getName(F));
}
// TargetLowering has info on library calls that CodeGen expects to be
// available, both from the C runtime and compiler-rt.
if (Lowering)
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.push_back(Name);
std::sort(Libcalls.begin(), Libcalls.end());
Libcalls.erase(std::unique(Libcalls.begin(), Libcalls.end()),
Libcalls.end());
}
void LTOCodeGenerator::applyScopeRestrictions() {
if (ScopeRestrictionsDone)
return;
@ -350,16 +390,19 @@ void LTOCodeGenerator::applyScopeRestrictions() {
Mangler Mangler(TargetMach);
std::vector<const char*> MustPreserveList;
SmallPtrSet<GlobalValue*, 8> AsmUsed;
std::vector<StringRef> Libcalls;
TargetLibraryInfo TLI(Triple(TargetMach->getTargetTriple()));
accumulateAndSortLibcalls(Libcalls, TLI, TargetMach->getTargetLowering());
for (Module::iterator f = mergedModule->begin(),
e = mergedModule->end(); f != e; ++f)
applyRestriction(*f, MustPreserveList, AsmUsed, Mangler);
applyRestriction(*f, Libcalls, MustPreserveList, AsmUsed, Mangler);
for (Module::global_iterator v = mergedModule->global_begin(),
e = mergedModule->global_end(); v != e; ++v)
applyRestriction(*v, MustPreserveList, AsmUsed, Mangler);
applyRestriction(*v, Libcalls, MustPreserveList, AsmUsed, Mangler);
for (Module::alias_iterator a = mergedModule->alias_begin(),
e = mergedModule->alias_end(); a != e; ++a)
applyRestriction(*a, MustPreserveList, AsmUsed, Mangler);
applyRestriction(*a, Libcalls, MustPreserveList, AsmUsed, Mangler);
GlobalVariable *LLVMCompilerUsed =
mergedModule->getGlobalVariable("llvm.compiler.used");