asm_inserter.cpp

#include "llvm/Pass.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/InlineAsm.h"
#include "llvm/Support/raw_ostream.h"

#include "llvm/IR/LegacyPassManager.h"
#include "llvm/Transforms/IPO/PassManagerBuilder.h"

using namespace llvm;

namespace {
struct AsmInserter : public FunctionPass {
  static char ID;
  AsmInserter() : FunctionPass(ID) {}

  bool runOnFunction(Function &F) override {
    bool changed = false;
    for (BasicBlock& BB : F) {
      for (Instruction& I : BB) {
        if (I.getOpcode() != Instruction::Call) {
          continue;
        }
        auto CI = cast<CallInst>(&I);
        if (CI->getCalledFunction()->isIntrinsic()) {
          continue;
        }
        auto fp_type = PointerType::get(CI->getFunctionType(), 0);
        auto iasm_type = FunctionType::get(fp_type, {fp_type}, false);
        auto iasm = InlineAsm::get(iasm_type, "", "=r,0", false);
        auto iasm_call_t = cast<FunctionType>(iasm->getType()->getPointerElementType());
        auto call = CallInst::Create(iasm_call_t, iasm, CI->getCalledFunction(), "", CI);
        CI->setCalledFunction(CI->getFunctionType(), call);
      }
    }
    return changed;
  }
}; // end of struct AsmInserter
}  // end of anonymous namespace

char AsmInserter::ID = 0;
static RegisterPass<AsmInserter> X("asm_inserter", "AsmInserter Pass",
                                   false /* Only looks at CFG */,
                                   false /* Analysis Pass */);

static RegisterStandardPasses Y(
    PassManagerBuilder::EP_EarlyAsPossible,
    [](const PassManagerBuilder &Builder,
       legacy::PassManagerBase &PM) { PM.add(new AsmInserter()); });