llvm dev - Feb 2015 - [LLVMdev] LTO regression test Bug 17623

Hello,

I have a fix for Bug17623 (http://llvm.org/bugs/show_bug.cgi?id=17623) but I am
not sure how best to install a regression test. The commands I use to run the
test are (approximately)

$LLVM/clang -flto -O2 -o BUG.o -c  BUG.c
$LLVM/llvm-lto -exported-symbol=main -o lto.o BUG.o
$LLVM/clang -o bug lto.o
./bug

Where the failing behavior is to seg fault and corrected behavior is to run to
completion.
The use of llvm-lto avoids a dependence on the native loader having appropriate
plugin support.

The reliance on running clang and code suggests a test belongs in the
llvm-test-suite. Could someone give me a pointer on how to configure a test
using commands like the above? Are there any other tests with a similar
structure?

Thanks
david
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On Feb 3, 2015 5:57 PM, "David Callahan" <dcallahan at fb.com>
wrote:
>
> Hello,
>
> I have a fix for Bug17623 (http://llvm.org/bugs/show_bug.cgi?id=17623)
but I am not sure how best to install a regression test. The commands I use
to run the test are (approximately)
>
> $LLVM/clang -flto -O2 -o BUG.o -c  BUG.c
> $LLVM/llvm-lto -exported-symbol=main -o lto.o BUG.o
> $LLVM/clang -o bug lto.o
> ./bug
>
> Where the failing behavior is to seg fault and corrected behavior is to
run to completion.
> The use of llvm-lto avoids a dependence on the native loader having
appropriate plugin support.
>
> The reliance on running clang and code suggests a test belongs in the
llvm-test-suite.

Not necessarily. It depends where the bug is. If clang is producing wrong
IR and needs to be changed, we just test clang and verify that the desired
IR doesn't have the erroneous feature that wr removed.

Alternatively, if clang is doing the right thing and the llvm IR linker is
mangling the result, or the llvm optimizations misunderstand - we should
just be able to construct the minimal IR that demonstrates the poor
behavior and verify llvm gets the right answer.

So where is the bug?
> Could someone give me a pointer on how to configure a test using commands
like the above? Are there any other tests with a similar
structure?
>
> Thanks
> david
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
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Thanks for the reply.

The bug is in the alias analysis (lib/Analysis/IPA/GlobalsModRef.cpp) where a
variable is not correctly seen as address-taken due to a static initializer.
This leads to an invalid loop invariant code motion and a subsequent use of a
bad pointer.

So clang is correct but  lto introduces a problem. I tried but was unable to
reproduce the problem with opt.
The bug can be reproduced with a .ll file but I don’t know how to verify the fix
other than running the output of LTO and so would welcome any suggestions.

david


From: David Blaikie <dblaikie at gmail.com<mailto:dblaikie at
gmail.com>>
Date: Tuesday, February 3, 2015 at 6:20 PM
To: David Callahan <dcallahan at fb.com<mailto:dcallahan at fb.com>>
Cc: LLVM Dev Mailing List <llvmdev at cs.uiuc.edu<mailto:llvmdev at
cs.uiuc.edu>>
Subject: Re: [LLVMdev] LTO regression test Bug 17623


On Feb 3, 2015 5:57 PM, "David Callahan" <dcallahan at
fb.com<mailto:dcallahan at fb.com>> wrote:
>
> Hello,
>
> I have a fix for Bug17623
(http://llvm.org/bugs/show_bug.cgi?id=17623<https://urldefense.proofpoint.com/v1/url?u=http://llvm.org/bugs/show_bug.cgi?id%3D17623&k=ZVNjlDMF0FElm4dQtryO4A%3D%3D%0A&r=8am7JZUn9ir%2BIPWQGSonqw%3D%3D%0A&m=%2B%2Bkxr1kNzm83C5RPkRlha1d0eUWXp7eVGgXWS%2F0MCDk%3D%0A&s=1fa398a9f03fc233090f7998fbbfd44c2cac26608bd90c07657af5f21ae80c85>)
but I am not sure how best to install a regression test. The commands I use to
run the test are (approximately)
>
> $LLVM/clang -flto -O2 -o BUG.o -c  BUG.c
> $LLVM/llvm-lto -exported-symbol=main -o lto.o BUG.o
> $LLVM/clang -o bug lto.o
> ./bug
>
> Where the failing behavior is to seg fault and corrected behavior is to run
to completion.
> The use of llvm-lto avoids a dependence on the native loader having
appropriate plugin support.
>
> The reliance on running clang and code suggests a test belongs in the
llvm-test-suite.
Not necessarily. It depends where the bug is. If clang is producing wrong IR and
needs to be changed, we just test clang and verify that the desired IR
doesn't have the erroneous feature that wr removed.

Alternatively, if clang is doing the right thing and the llvm IR linker is
mangling the result, or the llvm optimizations misunderstand - we should just be
able to construct the minimal IR that demonstrates the poor behavior and verify
llvm gets the right answer.

So where is the bug?
> Could someone give me a pointer on how to configure a test using commands
like the above? Are there any other tests with a
similar structure?
>
> Thanks
> david
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu<mailto:LLVMdev at cs.uiuc.edu>        
http://llvm.cs.uiuc.edu<https://urldefense.proofpoint.com/v1/url?u=http://llvm.cs.uiuc.edu&k=ZVNjlDMF0FElm4dQtryO4A%3D%3D%0A&r=8am7JZUn9ir%2BIPWQGSonqw%3D%3D%0A&m=%2B%2Bkxr1kNzm83C5RPkRlha1d0eUWXp7eVGgXWS%2F0MCDk%3D%0A&s=0cedb0184fc7b6271a3c209b247d747a6fe6d472e45329ba4b00fec538753bf4>
>
http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev<https://urldefense.proofpoint.com/v1/url?u=http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev&k=ZVNjlDMF0FElm4dQtryO4A%3D%3D%0A&r=8am7JZUn9ir%2BIPWQGSonqw%3D%3D%0A&m=%2B%2Bkxr1kNzm83C5RPkRlha1d0eUWXp7eVGgXWS%2F0MCDk%3D%0A&s=218b66c9dbe88e4a2ec30bfbe22cf49fa5e5dfe6b5e774878f4782d056fc2c90>
>
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