Hi On Wed, Nov 01, 2017 at 07:25:08AM -0700, Teresa Johnson wrote: > On Tue, Oct 31, 2017 at 5:42 PM, Michael Niedermayer <mich...@niedermayer.cc > > wrote: > > > Hi > > > > On Tue, Oct 31, 2017 at 04:29:18PM +0000, Teresa Johnson wrote: > > > It's needed for the same reason the used attribute was already added to > > the > > > "static const" variables. For those, when building with just -O2, they > > > could be removed by optimization since they had local (file) scope, and > > we > > > couldn't see the uses in the inline assembly (without the used > > attribute). > > > With ThinLTO we have whole program scope, so even though they are > > > non-static and have global scope we can do dead code elimination on them > > if > > > we don't see that they are used. > > > > currently we add "used" to DECLARE_ASM_CONST() > > which is specific to inline asm use. > > > > DECLARE_ALIGNED() is not specific to use in asm. > > > > For DECLARE_ASM_CONST() the "used" is unneeded only in the subset of > > inline asm cases where it is accessed through the asm operands like: > > __asm__ volatile( > > "movq %0, %%mm7 \n\t" > > "movq %1, %%mm6 \n\t" > > ::"m"(red_16mask),"m"(green_16mask)); > > > > The compiler has full vissibility here of the access and if it removes > > it its a compiler bug. > > > > this is compared to code like: > > "pand "MANGLE(mask24l)", %%mm0\n\t" > > > > Here the compiler has no easy vissibility of the use, it is part of > > the asm string. > > > > and comparing this to DECLARE_ALIGNED(), the big difference is > > that DECLARE_ALIGNED() is used by plain C code which never should need > > "used". So adding "used" to DECLARE_ALIGNED() would add alot more > > "unused detection overriding" than what is needed > > > > Perhaps then an additional macro is needed for variables that are currently > DECLARED_ALIGNED but used by MANGLE, which adds the used attribute. What do > you suggest?
Ive no specific suggestion, but a 2nd macro seems a option thanks [...] -- Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB it is not once nor twice but times without number that the same ideas make their appearance in the world. -- Aristotle
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