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Incorrect code generation of conditional compares for AArch64 #24833

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kbeyls opened this issue Aug 14, 2015 · 5 comments
Closed

Incorrect code generation of conditional compares for AArch64 #24833

kbeyls opened this issue Aug 14, 2015 · 5 comments
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@MatzeB
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backend:AArch64 bugzilla Issues migrated from bugzilla

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@kbeyls
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kbeyls commented Aug 14, 2015

Bugzilla Link 24459
Resolution FIXED
Resolved on Aug 20, 2015 18:34
Version trunk
OS All
Attachments reduced test case, Assembly produced by r242435 (correct), Assembly produced by r242436 (incorrect)
CC @MatzeB

Extended Description

It seems that http://llvm.org/viewvc/llvm-project?view=revision&revision=242436 introduced a correctness regression.
The attached reduced test case (still not tiny though) shows that at optimization level -O1, this code gets miscompiled, while it still was getting compiled correctly by clang r242436.

$ ./llvm.org/cmake-build-r242435/bin/clang ./reproducer/aarch64_tree_tests_reduce.c -S -O1 -o ./reproducer/t.242435.s;
$ ./llvm.org/cmake-build-r242436/bin/clang ./reproducer/aarch64_tree_tests_reduce.c -S -O1 -o ./reproducer/t.242436.s;
$ ./llvm.org/cmake-build-r242435/bin/clang ./reproducer/aarch64_tree_tests_reduce.c -O1 -o ./reproducer/t.242435.exe;
$ ./llvm.org/cmake-build-r242436/bin/clang ./reproducer/aarch64_tree_tests_reduce.c -O1 -o ./reproducer/t.242436.exe;
$ ./reproducer/t.242435.exe
$ ./reproducer/t.242436.exe
Expected: 0000000000000000 Got: 0000000000000000
@kbeyls
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kbeyls commented Aug 14, 2015

assigned to @MatzeB

@MatzeB
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MatzeB commented Aug 19, 2015

I tried reproducing this on llvm r245350 (and r245348) and cannot reproduce this on a aarch64-apple-ios target.

Could you provide the actual assembly for r242436 case instead of an executable?

@kbeyls
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kbeyls commented Aug 19, 2015

Assembly produced by r242436 (incorrect)
Apologies, I'm now attaching the assembly code I see coming out of r242436.

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kbeyls commented Aug 19, 2015

With the following command line options, cross-compiling from an x86 linux host, I can reproduce the same ccmp sequences that seem to be incorrect:

$ clang -target aarch64 -mcpu=generic -O1 aarch64_tree_tests_reduce.c -S
$ clang -target arm64-apple-ios -O1 aarch64_tree_tests_reduce.c -S

The -O1 optimization level is important to reproduce the problem: it does not manifest at other optimization levels.

I could reproduce this assembly from both r242436 and r245350.

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MatzeB commented Aug 21, 2015

Fixed in r245641.

@llvmbot llvmbot transferred this issue from llvm/llvm-bugzilla-archive Dec 10, 2021
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