http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57156
--- Comment #8 from Matthias Kretz <kretz at kde dot org> --- I just noticed the following in the Intel Optimization Reference Manual (Version 028 from July 2013), section 2.2 "Sandy Bridge": 2.2.3.1 Renamer [...] There is another dependency breaking idiom - the "ones idiom". • CMPEQ XMM1, XMM1; "ones idiom" set all elements to all "ones" In this case, the micro-op must execute, however, since it is known that regardless of the input data the output data is always "all ones" the micro-op dependency upon its sources does not exist as with the zero idiom and it can execute as soon as it finds a free execution port. Therefore I think it makes sense if this feature is exposed somehow. Right now, according to what you said, it is impossible to make use of this feature when programming with intrinsics. I see two solutions right now: 1. Let the cmpeq intrinsic reflect this special behavior: i.e. if the two inputs are the same variable, this behaves like a function without input. 2. Provide a new intrinsic/builtin analogous to _mm_setzero_* / _mm256_setzero_*
