llvm/lib/Transforms/Scalar/LowerWidenableCondition.cpp

   1 //===- LowerWidenableCondition.cpp - Lower the guard intrinsic ---------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This pass lowers the llvm.widenable.condition intrinsic to default value
  10 // which is i1 true.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "llvm/Transforms/Scalar/LowerWidenableCondition.h"
  15 #include "llvm/ADT/SmallVector.h"
  16 #include "llvm/IR/Function.h"
  17 #include "llvm/IR/InstIterator.h"
  18 #include "llvm/IR/Instructions.h"
  19 #include "llvm/IR/Intrinsics.h"
  20 #include "llvm/IR/Module.h"
  21 #include "llvm/IR/PatternMatch.h"
  22 #include "llvm/Transforms/Scalar.h"
  23
  24 using namespace llvm;
  25
  26 static bool lowerWidenableCondition(Function &F) {
  27   // Check if we can cheaply rule out the possibility of not having any work to
  28   // do.
  29   auto *WCDecl = F.getParent()->getFunction(
  30       Intrinsic::getName(Intrinsic::experimental_widenable_condition));
  31   if (!WCDecl || WCDecl->use_empty())
  32     return false;
  33
  34   using namespace llvm::PatternMatch;
  35   SmallVector<CallInst *, 8> ToLower;
  36   // Traverse through the users of WCDecl.
  37   // This is presumably cheaper than traversing all instructions in the
  38   // function.
  39   for (auto *U : WCDecl->users())
  40     if (auto *CI = dyn_cast<CallInst>(U))
  41       if (CI->getFunction() == &F)
  42         ToLower.push_back(CI);
  43
  44   if (ToLower.empty())
  45     return false;
  46
  47   for (auto *CI : ToLower) {
  48     CI->replaceAllUsesWith(ConstantInt::getTrue(CI->getContext()));
  49     CI->eraseFromParent();
  50   }
  51   return true;
  52 }
  53
  54 PreservedAnalyses LowerWidenableConditionPass::run(Function &F,
  55                                                FunctionAnalysisManager &AM) {
  56   if (lowerWidenableCondition(F))
  57     return PreservedAnalyses::none();
  58
  59   return PreservedAnalyses::all();
  60 }