1 //===-- GuardUtils.cpp - Utils for work with guards -------------*- C++ -*-===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 // Utils that are used to perform transformations related to guards and their
10 // conditions.
11 //===----------------------------------------------------------------------===//
12 
13 #include "llvm/Transforms/Utils/GuardUtils.h"
14 #include "llvm/IR/Function.h"
15 #include "llvm/IR/Instructions.h"
16 #include "llvm/IR/IRBuilder.h"
17 #include "llvm/IR/MDBuilder.h"
18 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
19 
20 using namespace llvm;
21 
22 static cl::opt<uint32_t> PredicatePassBranchWeight(
23     "guards-predicate-pass-branch-weight", cl::Hidden, cl::init(1 << 20),
24     cl::desc("The probability of a guard failing is assumed to be the "
25              "reciprocal of this value (default = 1 << 20)"));
26 
27 void llvm::makeGuardControlFlowExplicit(Function *DeoptIntrinsic,
28                                         CallInst *Guard) {
29   OperandBundleDef DeoptOB(*Guard->getOperandBundle(LLVMContext::OB_deopt));
30   SmallVector<Value *, 4> Args(std::next(Guard->arg_begin()), Guard->arg_end());
31 
32   auto *CheckBB = Guard->getParent();
33   auto *DeoptBlockTerm =
34       SplitBlockAndInsertIfThen(Guard->getArgOperand(0), Guard, true);
35 
36   auto *CheckBI = cast<BranchInst>(CheckBB->getTerminator());
37 
38   // SplitBlockAndInsertIfThen inserts control flow that branches to
39   // DeoptBlockTerm if the condition is true.  We want the opposite.
40   CheckBI->swapSuccessors();
41 
42   CheckBI->getSuccessor(0)->setName("guarded");
43   CheckBI->getSuccessor(1)->setName("deopt");
44 
45   if (auto *MD = Guard->getMetadata(LLVMContext::MD_make_implicit))
46     CheckBI->setMetadata(LLVMContext::MD_make_implicit, MD);
47 
48   MDBuilder MDB(Guard->getContext());
49   CheckBI->setMetadata(LLVMContext::MD_prof,
50                        MDB.createBranchWeights(PredicatePassBranchWeight, 1));
51 
52   IRBuilder<> B(DeoptBlockTerm);
53   auto *DeoptCall = B.CreateCall(DeoptIntrinsic, Args, {DeoptOB}, "");
54 
55   if (DeoptIntrinsic->getReturnType()->isVoidTy()) {
56     B.CreateRetVoid();
57   } else {
58     DeoptCall->setName("deoptcall");
59     B.CreateRet(DeoptCall);
60   }
61 
62   DeoptCall->setCallingConv(Guard->getCallingConv());
63   DeoptBlockTerm->eraseFromParent();
64 }
65