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/InitializePasses.h"
40#include "llvm/Pass.h"
41#include "llvm/Transforms/Utils/GuardUtils.h"
42
43using namespace llvm;
44
45static void turnToExplicitForm(CallInst *Guard, Function *DeoptIntrinsic) {
46 // Replace the guard with an explicit branch (just like in GuardWidening).
47 BasicBlock *OriginalBB = Guard->getParent();
48 (void)OriginalBB;
49 makeGuardControlFlowExplicit(DeoptIntrinsic, Guard, UseWC: true);
50 assert(isWidenableBranch(OriginalBB->getTerminator()) && "should hold");
51
52 Guard->eraseFromParent();
53}
54
55static bool explicifyGuards(Function &F) {
56 // Check if we can cheaply rule out the possibility of not having any work to
57 // do.
58 auto *GuardDecl = F.getParent()->getFunction(
59 Intrinsic::getName(Intrinsic::experimental_guard));
60 if (!GuardDecl || GuardDecl->use_empty())
61 return false;
62
63 SmallVector<CallInst *, 8> GuardIntrinsics;
64 for (auto &I : instructions(F))
65 if (isGuard(U: &I))
66 GuardIntrinsics.push_back(Elt: cast<CallInst>(Val: &I));
67
68 if (GuardIntrinsics.empty())
69 return false;
70
71 auto *DeoptIntrinsic = Intrinsic::getDeclaration(
72 F.getParent(), Intrinsic::experimental_deoptimize, {F.getReturnType()});
73 DeoptIntrinsic->setCallingConv(GuardDecl->getCallingConv());
74
75 for (auto *Guard : GuardIntrinsics)
76 turnToExplicitForm(Guard, DeoptIntrinsic);
77
78 return true;
79}
80
81PreservedAnalyses MakeGuardsExplicitPass::run(Function &F,
82 FunctionAnalysisManager &) {
83 if (explicifyGuards(F))
84 return PreservedAnalyses::none();
85 return PreservedAnalyses::all();
86}
87

source code of llvm/lib/Transforms/Scalar/MakeGuardsExplicit.cpp