LowerWidenableCondition.cpp

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//===- LowerWidenableCondition.cpp - Lower the guard intrinsic ---------------===//
//
// 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 pass lowers the llvm.widenable.condition intrinsic to default value
// which is i1 true.
//
//===----------------------------------------------------------------------===//
 
#include "llvm/Transforms/Scalar/LowerWidenableCondition.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/Transforms/Scalar.h"
 
using namespace llvm;
 
static bool lowerWidenableCondition(Function &F) {
  // Check if we can cheaply rule out the possibility of not having any work to
  // do.
  auto *WCDecl = Intrinsic::getDeclarationIfExists(
      F.getParent(), Intrinsic::experimental_widenable_condition);
  if (!WCDecl || WCDecl->use_empty())
    return false;
 
  using namespace llvm::PatternMatch;
  SmallVector<CallInst *, 8> ToLower;
  // Traverse through the users of WCDecl.
  // This is presumably cheaper than traversing all instructions in the
  // function.
  for (auto *U : WCDecl->users())
    if (auto *CI = dyn_cast<CallInst>(U))
      if (CI->getFunction() == &F)
        ToLower.push_back(CI);
 
  if (ToLower.empty())
    return false;
 
  for (auto *CI : ToLower) {
    CI->replaceAllUsesWith(ConstantInt::getTrue(CI->getContext()));
    CI->eraseFromParent();
  }
  return true;
}
 
PreservedAnalyses LowerWidenableConditionPass::run(Function &F,
                                               FunctionAnalysisManager &AM) {
  if (lowerWidenableCondition(F))
    return PreservedAnalyses::none();
 
  return PreservedAnalyses::all();
}