llvm/lib/Transforms/Scalar/LowerGuardIntrinsic.cpp

   1 //===- LowerGuardIntrinsic.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.experimental.guard intrinsic to a conditional call
  10 // to @llvm.experimental.deoptimize.  Once this happens, the guard can no longer
  11 // be widened.
  12 //
  13 //===----------------------------------------------------------------------===//
  14
  15 #include "llvm/Transforms/Scalar/LowerGuardIntrinsic.h"
  16 #include "llvm/ADT/SmallVector.h"
  17 #include "llvm/Analysis/GuardUtils.h"
  18 #include "llvm/IR/Function.h"
  19 #include "llvm/IR/InstIterator.h"
  20 #include "llvm/IR/Instructions.h"
  21 #include "llvm/IR/Intrinsics.h"
  22 #include "llvm/IR/Module.h"
  23 #include "llvm/Transforms/Utils/GuardUtils.h"
  24
  25 using namespace llvm;
  26
  27 static bool lowerGuardIntrinsic(Function &F) {
  28   // Check if we can cheaply rule out the possibility of not having any work to
  29   // do.
  30   auto *GuardDecl = F.getParent()->getFunction(
  31       Intrinsic::getName(Intrinsic::experimental_guard));
  32   if (!GuardDecl || GuardDecl->use_empty())
  33     return false;
  34
  35   SmallVector<CallInst *, 8> ToLower;
  36   // Traverse through the users of GuardDecl.
  37   // This is presumably cheaper than traversing all instructions in the
  38   // function.
  39   for (auto *U : GuardDecl->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   auto *DeoptIntrinsic = Intrinsic::getDeclaration(
  48       F.getParent(), Intrinsic::experimental_deoptimize, {F.getReturnType()});
  49   DeoptIntrinsic->setCallingConv(GuardDecl->getCallingConv());
  50
  51   for (auto *CI : ToLower) {
  52     makeGuardControlFlowExplicit(DeoptIntrinsic, CI, false);
  53     CI->eraseFromParent();
  54   }
  55
  56   return true;
  57 }
  58
  59 PreservedAnalyses LowerGuardIntrinsicPass::run(Function &F,
  60                                                FunctionAnalysisManager &AM) {
  61   if (lowerGuardIntrinsic(F))
  62     return PreservedAnalyses::none();
  63
  64   return PreservedAnalyses::all();
  65 }