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//===- RemoveAsmMemory.cpp - Remove ``asm("":::"memory")`` ----------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass removes all instances of ``asm("":::"memory")``.
//
//===----------------------------------------------------------------------===//
#include "llvm/ADT/Twine.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/InlineAsm.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Module.h"
#include "llvm/InstVisitor.h"
#include "llvm/Pass.h"
#include <string>
using namespace llvm;
namespace {
class RemoveAsmMemory : public FunctionPass {
public:
static char ID; // Pass identification, replacement for typeid
RemoveAsmMemory() : FunctionPass(ID) {
initializeRemoveAsmMemoryPass(*PassRegistry::getPassRegistry());
}
virtual bool runOnFunction(Function &F);
};
class AsmDirectivesVisitor : public InstVisitor<AsmDirectivesVisitor> {
public:
AsmDirectivesVisitor(Function &F)
: F(F), C(F.getParent()->getContext()), ModifiedFunction(false) {}
~AsmDirectivesVisitor() {}
bool modifiedFunction() const { return ModifiedFunction; }
/// Only Call Instructions are ever inline assembly directives.
void visitCallInst(CallInst &CI);
private:
Function &F;
LLVMContext &C;
bool ModifiedFunction;
AsmDirectivesVisitor() LLVM_DELETED_FUNCTION;
AsmDirectivesVisitor(const AsmDirectivesVisitor &) LLVM_DELETED_FUNCTION;
AsmDirectivesVisitor &operator=(
const AsmDirectivesVisitor &) LLVM_DELETED_FUNCTION;
};
}
char RemoveAsmMemory::ID = 0;
INITIALIZE_PASS(RemoveAsmMemory, "remove-asm-memory",
"remove all instances of ``asm(\"\":::\"memory\")``", false,
false)
bool RemoveAsmMemory::runOnFunction(Function &F) {
AsmDirectivesVisitor AV(F);
AV.visit(F);
return AV.modifiedFunction();
}
void AsmDirectivesVisitor::visitCallInst(CallInst &CI) {
if (!CI.isInlineAsm() ||
!cast<InlineAsm>(CI.getCalledValue())->isAsmMemory())
return;
// In NaCl ``asm("":::"memory")`` always comes in pairs, straddling a
// sequentially consistent fence. Other passes rewrite this fence to
// an equivalent stable NaCl intrinsic, meaning that this assembly can
// be removed.
CI.eraseFromParent();
ModifiedFunction = true;
}
namespace llvm {
FunctionPass *createRemoveAsmMemoryPass() { return new RemoveAsmMemory(); }
}
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