I think I can get it to fall back to -O1 which safe when it fails the test ,
but I don't know how to get it to add a flag if it fails a test , only how to
remove a flag if it fails a test, or we can just print a error message in
configure to say to use -fno-strict-aliasing
I think a fallback to -O1 is best
Jason
-------------------------------------------------------------------------
I imagine the performance hit is minimal . We have a simple testcase
int __attribute__((noinline))
foo(int i)
{
int *p = __builtin_malloc (4 * sizeof(int));
*p = 0;
p[i] = 1;
return *p;
}
extern void abort (void);
int main()
{
if (foo(0) != 1)
abort ();
return 0;
}
So we can reject the bad debian gcc-4.3.2 only , but I'm not sure how to get it
to select no-strict-aliasing if it fails the test.
Jason
----------------------------
Thanks for the information. I am forwarding this to mpir-devel to see
what Jason thinks about possibly disabling '-fstrict-aliasing'
upstream for builds on Debian gcc 4.3.2.
I wonder how much of a performance hit is involved.
Bill.
On 9 May 2012 16:23, leif <not.rea...@online.de> wrote:
> Jeroen Demeyer wrote:
>>
>> On 2012-05-06 23:22, Alexander Dreyer wrote:
>>>
>>> Hi!
>>> built and made ptestlong sucessfully on SuSE Enterprise 11.
>>>
>>> But I had to hack mpir to accept gcc 4.3.2 64bits: configure had
>>> hard-coded not to build on this platform, because the original gcc 4.3.2
>>> was buggy, but mine is patched. (The mpir guys do not test the actual
>>> bug, but just look for gcc's version.)
>>
>>
>> I agree, hardcoding that bad version isn't a good idea. Also because
>> MPIR might just work well enough to build GCC.
>
>
> Turns out that apparently only Debian's GCC 4.3.2 is affected (not vanilla
> FSF), and only if '-fstrict-aliasing' is enabled (which is the case with
> '-O2'.)
>
> See:
>
> http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=524472
>
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36765
>
>
> So we should probably patch MPIR's 'configure'.
>
>
> -leif
>
>
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