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[SimplifyCFG] Don't widen cond br if false branch has successors 

Fixes https://github.com/llvm/llvm-project/issues/57221.

This limits the tryWidenCondBranchToCondBranch transform making it
work only if the false block of widenable condition branch
has no successors.

If that block has successors, then SimplifyCondBranchToCondBranch
may undo the transform done by tryWidenCondBranchToCondBranch, which
would lead to infinite cycle of transformation and eventually
an assert failing.

Differential Revision: https://reviews.llvm.org/D132356
This commit is contained in:
Dmitry Makogon 2022-08-22 15:06:57 +07:00
parent 5d82819583
commit 9142f67ef2
2 changed files with 24 additions and 5 deletions
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5
llvm/lib/Transforms/Utils/SimplifyCFG.cpp
View File

@ -3999,6 +3999,11 @@ static bool tryWidenCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI,
return false;
if (!IfFalseBB->phis().empty())
return false; // TODO
// This helps avoid infinite loop with SimplifyCondBranchToCondBranch which
// may undo the transform done here.
// TODO: There might be a more fine-grained solution to this.
if (!llvm::succ_empty(IfFalseBB))
return false;
// Use lambda to lazily compute expensive condition after cheap ones.
auto NoSideEffects = [](BasicBlock &BB) {
return llvm::none_of(BB, [](const Instruction &I) {

24
llvm/test/Transforms/SimplifyCFG/pr52290.ll
View File

@ -1,15 +1,29 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt < %s -simplifycfg -S | FileCheck %s
; RUN: opt < %s -passes=simplifycfg -S | FileCheck %s
; XFAIL: *
; REQUIRES: asserts
; FIXME: Fails due to infinite loop in iterativelySimplifyCFG.
; ModuleID = 'test/Transforms/SimplifyCFG/pr-new.ll'
source_filename = "test/Transforms/SimplifyCFG/pr-new.ll"
define i32 @test(float %arg, i1 %c) gc "statepoint-example" personality i32* ()* @blam {
; CHECK-LABEL: @test
; CHECK-LABEL: @test(
; CHECK-NEXT: bb:
; CHECK-NEXT: [[TMP:%.*]] = call i1 @llvm.experimental.widenable.condition()
; CHECK-NEXT: br i1 [[TMP]], label [[BB2:%.*]], label [[BB1:%.*]]
; CHECK: bb1:
; CHECK-NEXT: br i1 [[C:%.*]], label [[BB7:%.*]], label [[BB5:%.*]]
; CHECK: bb2:
; CHECK-NEXT: [[TMP3:%.*]] = getelementptr inbounds i8, i8 addrspace(1)* undef, i64 16
; CHECK-NEXT: br i1 [[C]], label [[BB7]], label [[BB4:%.*]]
; CHECK: bb4:
; CHECK-NEXT: call void @snork() [ "deopt"() ]
; CHECK-NEXT: unreachable
; CHECK: bb5:
; CHECK-NEXT: ret i32 0
; CHECK: bb7:
; CHECK-NEXT: [[TMP8:%.*]] = call i32 (...) @llvm.experimental.deoptimize.i32(i32 10) [ "deopt"() ]
; CHECK-NEXT: ret i32 [[TMP8]]
;
bb:
%tmp = call i1 @llvm.experimental.widenable.condition()
br i1 %tmp, label %bb2, label %bb1