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
22using namespace llvm;
23
24static 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 M: F.getParent(), id: 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>(Val: U))
38 if (CI->getFunction() == &F)
39 ToLower.push_back(Elt: CI);
40
41 if (ToLower.empty())
42 return false;
43
44 auto *DeoptIntrinsic = Intrinsic::getOrInsertDeclaration(
45 M: F.getParent(), id: Intrinsic::experimental_deoptimize, Tys: {F.getReturnType()});
46 DeoptIntrinsic->setCallingConv(GuardDecl->getCallingConv());
47
48 for (auto *CI : ToLower) {
49 makeGuardControlFlowExplicit(DeoptIntrinsic, Guard: CI, UseWC: false);
50 CI->eraseFromParent();
51 }
52
53 return true;
54}
55
56PreservedAnalyses LowerGuardIntrinsicPass::run(Function &F,
57 FunctionAnalysisManager &AM) {
58 if (lowerGuardIntrinsic(F))
59 return PreservedAnalyses::none();
60
61 return PreservedAnalyses::all();
62}
63