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/IRBuilder.h"
37#include "llvm/IR/InstIterator.h"
38#include "llvm/IR/IntrinsicInst.h"
39#include "llvm/IR/Intrinsics.h"
40#include "llvm/InitializePasses.h"
41#include "llvm/Pass.h"
42#include "llvm/Transforms/Scalar.h"
43#include "llvm/Transforms/Utils/GuardUtils.h"
44
45using namespace llvm;
46
47namespace {
48struct MakeGuardsExplicitLegacyPass : public FunctionPass {
49  static char ID;
50  MakeGuardsExplicitLegacyPass() : FunctionPass(ID) {
51    initializeMakeGuardsExplicitLegacyPassPass(*PassRegistry::getPassRegistry());
52  }
53
54  bool runOnFunction(Function &F) override;
55};
56}
57
58static void turnToExplicitForm(CallInst *Guard, Function *DeoptIntrinsic) {
59  // Replace the guard with an explicit branch (just like in GuardWidening).
60  BasicBlock *OriginalBB = Guard->getParent();
61  (void)OriginalBB;
62  makeGuardControlFlowExplicit(DeoptIntrinsic, Guard, true);
63  assert(isWidenableBranch(OriginalBB->getTerminator()) && "should hold");
64
65  Guard->eraseFromParent();
66}
67
68static bool explicifyGuards(Function &F) {
69  // Check if we can cheaply rule out the possibility of not having any work to
70  // do.
71  auto *GuardDecl = F.getParent()->getFunction(
72      Intrinsic::getName(Intrinsic::experimental_guard));
73  if (!GuardDecl || GuardDecl->use_empty())
74    return false;
75
76  SmallVector<CallInst *, 8> GuardIntrinsics;
77  for (auto &I : instructions(F))
78    if (isGuard(&I))
79      GuardIntrinsics.push_back(cast<CallInst>(&I));
80
81  if (GuardIntrinsics.empty())
82    return false;
83
84  auto *DeoptIntrinsic = Intrinsic::getDeclaration(
85      F.getParent(), Intrinsic::experimental_deoptimize, {F.getReturnType()});
86  DeoptIntrinsic->setCallingConv(GuardDecl->getCallingConv());
87
88  for (auto *Guard : GuardIntrinsics)
89    turnToExplicitForm(Guard, DeoptIntrinsic);
90
91  return true;
92}
93
94bool MakeGuardsExplicitLegacyPass::runOnFunction(Function &F) {
95  return explicifyGuards(F);
96}
97
98char MakeGuardsExplicitLegacyPass::ID = 0;
99INITIALIZE_PASS(MakeGuardsExplicitLegacyPass, "make-guards-explicit",
100                "Lower the guard intrinsic to explicit control flow form",
101                false, false)
102
103PreservedAnalyses MakeGuardsExplicitPass::run(Function &F,
104                                           FunctionAnalysisManager &) {
105  if (explicifyGuards(F))
106    return PreservedAnalyses::none();
107  return PreservedAnalyses::all();
108}
109