[Bug middle-end/64554] using _mm_clmulepi64_si128 doesn't error with -O0

["jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64554

--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #6)
> (In reply to charles from comment #5)
> > No you're right.
> > 
> > I could add, though, that the compiler should have said something.
> > 
> > Also, why did it compile just fine with -O0?
> 
> Sounds like a bug (we should error immediately here IMHO).  Probably
> needs to annotate the CIF codes with whether this is "fatal" (won't
> change with other inlining, IPA or LTO).
> 
> OTOH the headers are also poorly designed to trigger this kind of error.
> 
> Maybe we want to support __attribute__((always_inline("ISA not enabled")))
> instead to be able to print a custom error message?

The difference is that for __OPTIMIZE__   _mm_clmulepi64_si128 is implemented
as always_inline function (surrounded by #pragma GCC target("pclmul")), so for
-O1+ the inlining error is expected, such function can't be inlined into the
current function, and always_inline mandates that it is inlined (without
always_inline it would simply not be inlined, and the out of line
_mm_clmulepi64_si128 would use the pclmul ISA, while the caller would not).

For -O0, this is implemented using a macro, since the last argument must be a
constant, and the reason you get no error is that the function is const and you
don't use the result, so it is DCEd.
If you actually use the result (at -O0 it is enough to store it into say
__m128i c = _mm_clmulepi64_si128(a, b, 1); , for -O1 you'd need something
better, store into volatile var, or global var or otherwise make sure it isn't
DCEd), then you get this diagnosed:

/tmp/z.c: In function ‘main’:
/tmp/z.c:6:11: error: ‘__builtin_ia32_pclmulqdq128’ needs isa option -m32
-mpclmul
   __m128i c = _mm_clmulepi64_si128(a, b, 1);
           ^

So I don't see any bug on the gcc side here.
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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/64535] Emergency buffer for exception allocation too small
Date: Mon, 12 Jan 2015 10:10:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idd535

--- Comment #9 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
If all allocations from the emergency pool are at least
sizeof(__cxa_refcounted_exception) long (or what is the minimum), then trying
to split the memory into smaller chunks (down to sizeof(free_entry)) might be
counter-productive.