1 //===- MakeGuardsExplicit.cpp - Turn guard intrinsics into guard branches -===//
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 the new form of
10 // guard represented as widenable explicit branch to the deopt block. The
11 // difference between this pass and LowerGuardIntrinsic is that after this pass
12 // the guard represented as intrinsic:
13 //
14 // call void(i1, ...) @llvm.experimental.guard(i1 %old_cond) [ "deopt"() ]
15 //
16 // transforms to a guard represented as widenable explicit branch:
17 //
18 // %widenable_cond = call i1 @llvm.experimental.widenable.condition()
19 // br i1 (%old_cond & %widenable_cond), label %guarded, label %deopt
20 //
21 // Here:
22 // - The semantics of @llvm.experimental.widenable.condition allows to replace
23 // %widenable_cond with the construction (%widenable_cond & %any_other_cond)
24 // without loss of correctness;
25 // - %guarded is the lower part of old guard intrinsic's parent block split by
26 // the intrinsic call;
27 // - %deopt is a block containing a sole call to @llvm.experimental.deoptimize
28 // intrinsic.
29 //
30 // Therefore, this branch preserves the property of widenability.
31 //
32 //===----------------------------------------------------------------------===//
33
34 #include "llvm/Transforms/Scalar/MakeGuardsExplicit.h"
35 #include "llvm/Analysis/GuardUtils.h"
36 #include "llvm/IR/InstIterator.h"
37 #include "llvm/IR/Instructions.h"
38 #include "llvm/IR/Intrinsics.h"
39 #include "llvm/IR/Module.h"
40 #include "llvm/InitializePasses.h"
41 #include "llvm/Pass.h"
42 #include "llvm/Transforms/Utils/GuardUtils.h"
43
44 using namespace llvm;
45
turnToExplicitForm(CallInst * Guard,Function * DeoptIntrinsic)46 static void turnToExplicitForm(CallInst *Guard, Function *DeoptIntrinsic) {
47 // Replace the guard with an explicit branch (just like in GuardWidening).
48 BasicBlock *OriginalBB = Guard->getParent();
49 (void)OriginalBB;
50 makeGuardControlFlowExplicit(DeoptIntrinsic, Guard, true);
51 assert(isWidenableBranch(OriginalBB->getTerminator()) && "should hold");
52
53 Guard->eraseFromParent();
54 }
55
explicifyGuards(Function & F)56 static bool explicifyGuards(Function &F) {
57 // Check if we can cheaply rule out the possibility of not having any work to
58 // do.
59 auto *GuardDecl = F.getParent()->getFunction(
60 Intrinsic::getName(Intrinsic::experimental_guard));
61 if (!GuardDecl || GuardDecl->use_empty())
62 return false;
63
64 SmallVector<CallInst *, 8> GuardIntrinsics;
65 for (auto &I : instructions(F))
66 if (isGuard(&I))
67 GuardIntrinsics.push_back(cast<CallInst>(&I));
68
69 if (GuardIntrinsics.empty())
70 return false;
71
72 auto *DeoptIntrinsic = Intrinsic::getDeclaration(
73 F.getParent(), Intrinsic::experimental_deoptimize, {F.getReturnType()});
74 DeoptIntrinsic->setCallingConv(GuardDecl->getCallingConv());
75
76 for (auto *Guard : GuardIntrinsics)
77 turnToExplicitForm(Guard, DeoptIntrinsic);
78
79 return true;
80 }
81
run(Function & F,FunctionAnalysisManager &)82 PreservedAnalyses MakeGuardsExplicitPass::run(Function &F,
83 FunctionAnalysisManager &) {
84 if (explicifyGuards(F))
85 return PreservedAnalyses::none();
86 return PreservedAnalyses::all();
87 }
88