1 //===- LowerGuardIntrinsic.cpp - Lower the guard intrinsic ---------------===//
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 //
10 // This pass lowers the llvm.experimental.guard intrinsic to a conditional call
11 // to @llvm.experimental.deoptimize. Once this happens, the guard can no longer
12 // be widened.
13 //
14 //===----------------------------------------------------------------------===//
15
16 #include "llvm/Transforms/Scalar.h"
17 #include "llvm/ADT/SmallVector.h"
18 #include "llvm/IR/BasicBlock.h"
19 #include "llvm/IR/Function.h"
20 #include "llvm/IR/InstIterator.h"
21 #include "llvm/IR/Instructions.h"
22 #include "llvm/IR/Intrinsics.h"
23 #include "llvm/IR/IRBuilder.h"
24 #include "llvm/IR/MDBuilder.h"
25 #include "llvm/IR/Module.h"
26 #include "llvm/Pass.h"
27 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
28
29 using namespace llvm;
30
31 static cl::opt<uint32_t> PredicatePassBranchWeight(
32 "guards-predicate-pass-branch-weight", cl::Hidden, cl::init(1 << 20),
33 cl::desc("The probability of a guard failing is assumed to be the "
34 "reciprocal of this value (default = 1 << 20)"));
35
36 namespace {
37 struct LowerGuardIntrinsic : public FunctionPass {
38 static char ID;
LowerGuardIntrinsic__anon03ac00840111::LowerGuardIntrinsic39 LowerGuardIntrinsic() : FunctionPass(ID) {
40 initializeLowerGuardIntrinsicPass(*PassRegistry::getPassRegistry());
41 }
42
43 bool runOnFunction(Function &F) override;
44 };
45 }
46
MakeGuardControlFlowExplicit(Function * DeoptIntrinsic,CallInst * CI)47 static void MakeGuardControlFlowExplicit(Function *DeoptIntrinsic,
48 CallInst *CI) {
49 OperandBundleDef DeoptOB(*CI->getOperandBundle(LLVMContext::OB_deopt));
50 SmallVector<Value *, 4> Args(std::next(CI->arg_begin()), CI->arg_end());
51
52 auto *CheckBB = CI->getParent();
53 auto *DeoptBlockTerm =
54 SplitBlockAndInsertIfThen(CI->getArgOperand(0), CI, true);
55
56 auto *CheckBI = cast<BranchInst>(CheckBB->getTerminator());
57
58 // SplitBlockAndInsertIfThen inserts control flow that branches to
59 // DeoptBlockTerm if the condition is true. We want the opposite.
60 CheckBI->swapSuccessors();
61
62 CheckBI->getSuccessor(0)->setName("guarded");
63 CheckBI->getSuccessor(1)->setName("deopt");
64
65 if (auto *MD = CI->getMetadata(LLVMContext::MD_make_implicit))
66 CheckBI->setMetadata(LLVMContext::MD_make_implicit, MD);
67
68 MDBuilder MDB(CI->getContext());
69 CheckBI->setMetadata(LLVMContext::MD_prof,
70 MDB.createBranchWeights(PredicatePassBranchWeight, 1));
71
72 IRBuilder<> B(DeoptBlockTerm);
73 auto *DeoptCall = B.CreateCall(DeoptIntrinsic, Args, {DeoptOB}, "");
74
75 if (DeoptIntrinsic->getReturnType()->isVoidTy()) {
76 B.CreateRetVoid();
77 } else {
78 DeoptCall->setName("deoptcall");
79 B.CreateRet(DeoptCall);
80 }
81
82 DeoptCall->setCallingConv(CI->getCallingConv());
83 DeoptBlockTerm->eraseFromParent();
84 }
85
runOnFunction(Function & F)86 bool LowerGuardIntrinsic::runOnFunction(Function &F) {
87 // Check if we can cheaply rule out the possibility of not having any work to
88 // do.
89 auto *GuardDecl = F.getParent()->getFunction(
90 Intrinsic::getName(Intrinsic::experimental_guard));
91 if (!GuardDecl || GuardDecl->use_empty())
92 return false;
93
94 SmallVector<CallInst *, 8> ToLower;
95 for (auto &I : instructions(F))
96 if (auto *CI = dyn_cast<CallInst>(&I))
97 if (auto *F = CI->getCalledFunction())
98 if (F->getIntrinsicID() == Intrinsic::experimental_guard)
99 ToLower.push_back(CI);
100
101 if (ToLower.empty())
102 return false;
103
104 auto *DeoptIntrinsic = Intrinsic::getDeclaration(
105 F.getParent(), Intrinsic::experimental_deoptimize, {F.getReturnType()});
106 DeoptIntrinsic->setCallingConv(GuardDecl->getCallingConv());
107
108 for (auto *CI : ToLower) {
109 MakeGuardControlFlowExplicit(DeoptIntrinsic, CI);
110 CI->eraseFromParent();
111 }
112
113 return true;
114 }
115
116 char LowerGuardIntrinsic::ID = 0;
117 INITIALIZE_PASS(LowerGuardIntrinsic, "lower-guard-intrinsic",
118 "Lower the guard intrinsic to normal control flow", false,
119 false)
120
createLowerGuardIntrinsicPass()121 Pass *llvm::createLowerGuardIntrinsicPass() {
122 return new LowerGuardIntrinsic();
123 }
124