[Bug middle-end/38671] [4.4 Regression] extra code for setting up loops (IV-opts and 32bits vs 64bits)

[tim at klingt dot org]

------- Comment #6 from tim at klingt dot org  2008-12-31 09:20 -------
> sys_perf_counter_open always returns less than zero for me. 
> This is with:
> Linux gcc13 2.6.18-6-vserver-amd64 #1 SMP Sun Feb 10 17:55:04 UTC 2008 x86_64
> GNU/Linux
> 
> What system call is it trying to do and why?
> 

it is trying to open the performance counters
(http://lwn.net/Articles/310176/). it requires a patched kernel, though ...


(In reply to comment #3)
> t.cc: In function �float __vector__ nova::detail::gen_one()�:
> t.cc:34160: warning: �x� is used uninitialized in this function
> 
> inline __m128 gen_one(void)
> {
>     __m128i x;
>     __m128i ones = _mm_cmpeq_epi32(x, x);
>     return (__m128)_mm_slli_epi32 (_mm_srli_epi32(ones, 25), 23);
> }
> 
> Is undefined code I think.

this code is valid. the uninitialized xmm register x is compared with itself in
order to set the register ones to ffffffffffffffffffffffffffffffff.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38671