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/IR/Function.h"
18 #include "llvm/IR/Instructions.h"
19 #include "llvm/IR/Intrinsics.h"
20 #include "llvm/Transforms/Utils/GuardUtils.h"
21
22 using namespace llvm;
23
lowerGuardIntrinsic(Function & F)24 static bool lowerGuardIntrinsic(Function &F) {
25 // Check if we can cheaply rule out the possibility of not having any work to
26 // do.
27 auto *GuardDecl = Intrinsic::getDeclarationIfExists(
28 F.getParent(), Intrinsic::experimental_guard);
29 if (!GuardDecl || GuardDecl->use_empty())
30 return false;
31
32 SmallVector<CallInst *, 8> ToLower;
33 // Traverse through the users of GuardDecl.
34 // This is presumably cheaper than traversing all instructions in the
35 // function.
36 for (auto *U : GuardDecl->users())
37 if (auto *CI = dyn_cast<CallInst>(U))
38 if (CI->getFunction() == &F)
39 ToLower.push_back(CI);
40
41 if (ToLower.empty())
42 return false;
43
44 auto *DeoptIntrinsic = Intrinsic::getOrInsertDeclaration(
45 F.getParent(), Intrinsic::experimental_deoptimize, {F.getReturnType()});
46 DeoptIntrinsic->setCallingConv(GuardDecl->getCallingConv());
47
48 for (auto *CI : ToLower) {
49 makeGuardControlFlowExplicit(DeoptIntrinsic, CI, false);
50 CI->eraseFromParent();
51 }
52
53 return true;
54 }
55
run(Function & F,FunctionAnalysisManager & AM)56 PreservedAnalyses LowerGuardIntrinsicPass::run(Function &F,
57 FunctionAnalysisManager &AM) {
58 if (lowerGuardIntrinsic(F))
59 return PreservedAnalyses::none();
60
61 return PreservedAnalyses::all();
62 }
63