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 }
64