[LLVMdev] Help needed on debugging llvm

[Anitha Boyapati]

On 6 November 2012 14:53, Duncan Sands <baldrick at free.fr> wrote:

> Hi Anitha,
>
>
> On 05/11/12 10:29, Anitha Boyapati wrote:
>
>>
>>
>> On 5 November 2012 14:32, Duncan Sands <baldrick at free.fr
>> <mailto:baldrick at free.fr>> wrote:
>>
>>     Hi Anitha,
>>
>>
>>         http://llvm.org/bugs/show_bug.**__cgi?id=14185<http://llvm.org/bugs/show_bug.__cgi?id=14185>
>>
>>         <http://llvm.org/bugs/show_**bug.cgi?id=14185<http://llvm.org/bugs/show_bug.cgi?id=14185>
>> >
>>         I am stuck on analysis. Does any one have alternate suggestions
>> on debugging
>>         llvm? (Please refer to comments for the work done so far)
>>
>>
>>     try to reduce a small standalone testcase which is an LLVM IR (.ll)
>> file
>>
>> Yes. Unfortunately, that is the challenge at the moment.
>>
>
> did you reduce everything down to one problematic source file?  If so, you
> can
> then start moving stuff out of that file to an auxiliary file until you
> only
> have left a minimal core that shows the problem.  But maybe you did that
> already?
>

I could corner down the segfault to a single function in source file. But
the problem is - if that function is responsible for segfault or if it is
the optimization somewhere else that is driving the segfault. In the worst
case it could be so. I am yet to dive deeper there.

Meanwhile, I have some question w.r.t "-fplugin-arg-dragonegg-emit-ir".
Lets say I use the following command:

[1]. g++  -O2 -march=bdver2 fplugin=dragonegg.so -mno-fma -mfma4
-fplugin-arg-dragonegg-emit-ir -S -ffast-math <test.c> -o <test.ll>

Does the above command produce an IR that is already optimized because of
"-O2 -ffast-math -mno-fma -mfma4" ?

[2]. If I feed the above generated <test.ll> to clang as follows:

clang  -O3 -march=bdver2 -mno-fma  -mfma4 -ffp-contract=fast <test.ll>

Does clang proceed to optimize the test.ll w.r.t "-O3 -ffp-contract=fast
-mno-fma -mfma4" ? (I am not sure if -ffp-contract=fast has any effect
there, but I could be wrong though)

Also thanks for the immediate fix for __builtin_iceil(). I can see that the
issue got resolved.

-Anitha
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