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/Analysis/GuardUtils.h"
18 #include "llvm/IR/Function.h"
19 #include "llvm/IR/InstIterator.h"
20 #include "llvm/IR/Instructions.h"
21 #include "llvm/IR/Intrinsics.h"
22 #include "llvm/IR/Module.h"
23 #include "llvm/InitializePasses.h"
24 #include "llvm/Pass.h"
25 #include "llvm/Transforms/Scalar.h"
26 #include "llvm/Transforms/Utils/GuardUtils.h"
27 
28 using namespace llvm;
29 
30 namespace {
31 struct LowerGuardIntrinsicLegacyPass : public FunctionPass {
32   static char ID;
33   LowerGuardIntrinsicLegacyPass() : FunctionPass(ID) {
34     initializeLowerGuardIntrinsicLegacyPassPass(
35         *PassRegistry::getPassRegistry());
36   }
37 
38   bool runOnFunction(Function &F) override;
39 };
40 }
41 
42 static bool lowerGuardIntrinsic(Function &F) {
43   // Check if we can cheaply rule out the possibility of not having any work to
44   // do.
45   auto *GuardDecl = F.getParent()->getFunction(
46       Intrinsic::getName(Intrinsic::experimental_guard));
47   if (!GuardDecl || GuardDecl->use_empty())
48     return false;
49 
50   SmallVector<CallInst *, 8> ToLower;
51   // Traverse through the users of GuardDecl.
52   // This is presumably cheaper than traversing all instructions in the
53   // function.
54   for (auto *U : GuardDecl->users())
55     if (auto *CI = dyn_cast<CallInst>(U))
56       if (CI->getFunction() == &F)
57         ToLower.push_back(CI);
58 
59   if (ToLower.empty())
60     return false;
61 
62   auto *DeoptIntrinsic = Intrinsic::getDeclaration(
63       F.getParent(), Intrinsic::experimental_deoptimize, {F.getReturnType()});
64   DeoptIntrinsic->setCallingConv(GuardDecl->getCallingConv());
65 
66   for (auto *CI : ToLower) {
67     makeGuardControlFlowExplicit(DeoptIntrinsic, CI, false);
68     CI->eraseFromParent();
69   }
70 
71   return true;
72 }
73 
74 bool LowerGuardIntrinsicLegacyPass::runOnFunction(Function &F) {
75   return lowerGuardIntrinsic(F);
76 }
77 
78 char LowerGuardIntrinsicLegacyPass::ID = 0;
79 INITIALIZE_PASS(LowerGuardIntrinsicLegacyPass, "lower-guard-intrinsic",
80                 "Lower the guard intrinsic to normal control flow", false,
81                 false)
82 
83 Pass *llvm::createLowerGuardIntrinsicPass() {
84   return new LowerGuardIntrinsicLegacyPass();
85 }
86 
87 PreservedAnalyses LowerGuardIntrinsicPass::run(Function &F,
88                                                FunctionAnalysisManager &AM) {
89   if (lowerGuardIntrinsic(F))
90     return PreservedAnalyses::none();
91 
92   return PreservedAnalyses::all();
93 }
94