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//===- RewriteAsmDirectives.cpp - Handle Architecture-Independent Assembly-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass rewrites any inline assembly directive which is portable
// into LLVM bitcode.
//
//===----------------------------------------------------------------------===//
#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 RewriteAsmDirectives : public FunctionPass {
public:
static char ID; // Pass identification, replacement for typeid
RewriteAsmDirectives() : FunctionPass(ID) {
initializeRewriteAsmDirectivesPass(*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 RewriteAsmDirectives::ID = 0;
INITIALIZE_PASS(
RewriteAsmDirectives, "rewrite-asm-directives",
"rewrite portable inline assembly directives into non-asm LLVM IR",
false, false)
bool RewriteAsmDirectives::runOnFunction(Function &F) {
AsmDirectivesVisitor AV(F);
AV.visit(F);
return AV.modifiedFunction();
}
void AsmDirectivesVisitor::visitCallInst(CallInst &CI) {
if (!CI.isInlineAsm())
return;
Instruction *Replacement = NULL;
InlineAsm *IA = cast<InlineAsm>(CI.getCalledValue());
std::string AsmStr(IA->getAsmString());
std::string ConstraintStr(IA->getConstraintString());
Type *T = CI.getType();
bool isEmptyAsm = AsmStr.empty();
// Different triples will encode "touch everything" differently, e.g.:
// - le32-unknown-nacl has "~{memory}".
// - x86 "~{memory},~{dirflag},~{fpsr},~{flags}".
// The following code therefore only searches for memory: this pass
// deals with portable assembly, touching anything else than memory in
// an empty assembly statement is meaningless.
bool touchesMemory = ConstraintStr.find("~{memory}") != std::string::npos;
if (T->isVoidTy() && IA->hasSideEffects() && isEmptyAsm && touchesMemory) {
// asm("":::"memory") => fence seq_cst
// This transformation is safe and strictly stronger: the former is
// purely a compiler fence, whereas the latter is a compiler fence
// as well as a hardware fence which orders all loads and stores on
// the current thread of execution.
Replacement = new FenceInst(C, SequentiallyConsistent, CrossThread, &CI);
}
if (Replacement) {
Replacement->setDebugLoc(CI.getDebugLoc());
CI.replaceAllUsesWith(Replacement);
CI.eraseFromParent();
ModifiedFunction = true;
}
}
namespace llvm {
FunctionPass *createRewriteAsmDirectivesPass() {
return new RewriteAsmDirectives();
}
}
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