[JumpThreading] Assertion `!contains(New, this) && "this->replaceAllUsesWith(expr(this)) is NOT valid!"' failed. #58812
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EugeneZelenko
added
llvm:optimizations
crash
nikic
changed the title
|
Reduced: ; RUN: opt -S -jump-threading < %s
define void @test() {
entry:
br i1 false, label %loop, label %exit
loop:
%bool = phi i1 [ %xor, %loop.latch ], [ false, %entry ]
%cmp = icmp eq i16 0, 1
%xor = xor i1 %cmp, %bool
br i1 %bool, label %loop.latch, label %exit
loop.latch:
%dummy = phi i16 [ 0, %loop ]
br label %loop
exit:
ret void
} |
|
Hi @nikic ! Thanks for this amazing reduced IR! This loop looks like dead code because the entry block jumps directly to exit. Should we arrange *DCE before JumpThreading in the pipeline? Locally I made a patch solved this issue that check diff --git a/llvm/lib/Transforms/Scalar/JumpThreading.cpp b/llvm/lib/Transforms/Scalar/JumpThreading.cpp
index 75bc4bb76260..43fdfd225150 100644
--- a/llvm/lib/Transforms/Scalar/JumpThreading.cpp
+++ b/llvm/lib/Transforms/Scalar/JumpThreading.cpp
@@ -1932,7 +1932,7 @@ bool JumpThreadingPass::processBranchOnXOR(BinaryOperator *BO) {
// If all preds provide undef, just nuke the xor, because it is undef too.
BO->replaceAllUsesWith(UndefValue::get(BO->getType()));
BO->eraseFromParent();
- } else if (SplitVal->isZero()) {
+ } else if (SplitVal->isZero() && BO != BO->getOperand(isLHS)) {
// If all preds provide 0, replace the xor with the other input.
BO->replaceAllUsesWith(BO->getOperand(isLHS));
BO->eraseFromParent(); |
|
JumpThreading already removes unreachable blocks before it runs. However, new ones may be introduced as a result of transforms. It's either necessary to consistently remove them during transforms (this is probably hard because JT cannot use DT for compile-time reasons) or be robust against unreachable code. |
CarlosAlbertoEnciso
pushed a commit
to SNSystems/llvm-debuginfo-analyzer
that referenced
this issue
Dec 25, 2022
Reproducer:
; RUN: opt -S -jump-threading < %s
define void @test() {
entry:
br i1 false, label %loop, label %exit
loop:
%bool = phi i1 [ %xor, %loop.latch ], [ false, %entry ]
%cmp = icmp eq i16 0, 1
%xor = xor i1 %cmp, %bool
br i1 %bool, label %loop.latch, label %exit
loop.latch:
%dummy = phi i16 [ 0, %loop ]
br label %loop
exit:
ret void
}
On this occassion, phi node %bool is actually %xor, and doing substitution causes assertion failure.
Fixes: llvm/llvm-project#58812
Reviewed By: nikic
Differential Revision: https://reviews.llvm.org/D139783
veselypeta
pushed a commit
to veselypeta/cherillvm
that referenced
this issue
Jun 10, 2024
Reproducer:
; RUN: opt -S -jump-threading < %s
define void @test() {
entry:
br i1 false, label %loop, label %exit
loop:
%bool = phi i1 [ %xor, %loop.latch ], [ false, %entry ]
%cmp = icmp eq i16 0, 1
%xor = xor i1 %cmp, %bool
br i1 %bool, label %loop.latch, label %exit
loop.latch:
%dummy = phi i16 [ 0, %loop ]
br label %loop
exit:
ret void
}
On this occassion, phi node %bool is actually %xor, and doing substitution causes assertion failure.
Fixes: llvm/llvm-project#58812
Reviewed By: nikic
Differential Revision: https://reviews.llvm.org/D139783
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Godbolt repro: https://godbolt.org/z/M4brh6cGo
Run clang++ on the following test:
Test.cpp.txt
Backtrace:
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