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