lib/Transforms/Utils/GuardUtils.cpp

   1 //===-- GuardUtils.cpp - Utils for work with guards -------------*- C++ -*-===//
   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 // Utils that are used to perform transformations related to guards and their
   9 // conditions.
  10 //===----------------------------------------------------------------------===//
  11
  12 #include "llvm/Transforms/Utils/GuardUtils.h"
  13 #include "llvm/IR/Function.h"
  14 #include "llvm/IR/Instructions.h"
  15 #include "llvm/IR/IRBuilder.h"
  16 #include "llvm/IR/MDBuilder.h"
  17 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
  18
  19 using namespace llvm;
  20
  21 static cl::opt<uint32_t> PredicatePassBranchWeight(
  22     "guards-predicate-pass-branch-weight", cl::Hidden, cl::init(1 << 20),
  23     cl::desc("The probability of a guard failing is assumed to be the "
  24              "reciprocal of this value (default = 1 << 20)"));
  25
  26 void llvm::makeGuardControlFlowExplicit(Function *DeoptIntrinsic,
  27                                         CallInst *Guard) {
  28   OperandBundleDef DeoptOB(*Guard->getOperandBundle(LLVMContext::OB_deopt));
  29   SmallVector<Value *, 4> Args(std::next(Guard->arg_begin()), Guard->arg_end());
  30
  31   auto *CheckBB = Guard->getParent();
  32   auto *DeoptBlockTerm =
  33       SplitBlockAndInsertIfThen(Guard->getArgOperand(0), Guard, true);
  34
  35   auto *CheckBI = cast<BranchInst>(CheckBB->getTerminator());
  36
  37   // SplitBlockAndInsertIfThen inserts control flow that branches to
  38   // DeoptBlockTerm if the condition is true.  We want the opposite.
  39   CheckBI->swapSuccessors();
  40
  41   CheckBI->getSuccessor(0)->setName("guarded");
  42   CheckBI->getSuccessor(1)->setName("deopt");
  43
  44   if (auto *MD = Guard->getMetadata(LLVMContext::MD_make_implicit))
  45     CheckBI->setMetadata(LLVMContext::MD_make_implicit, MD);
  46
  47   MDBuilder MDB(Guard->getContext());
  48   CheckBI->setMetadata(LLVMContext::MD_prof,
  49                        MDB.createBranchWeights(PredicatePassBranchWeight, 1));
  50
  51   IRBuilder<> B(DeoptBlockTerm);
  52   auto *DeoptCall = B.CreateCall(DeoptIntrinsic, Args, {DeoptOB}, "");
  53
  54   if (DeoptIntrinsic->getReturnType()->isVoidTy()) {
  55     B.CreateRetVoid();
  56   } else {
  57     DeoptCall->setName("deoptcall");
  58     B.CreateRet(DeoptCall);
  59   }
  60
  61   DeoptCall->setCallingConv(Guard->getCallingConv());
  62   DeoptBlockTerm->eraseFromParent();
  63 }