> The C constraint on x86 is defined, in both the doc and the comments, as > "constant that can be easily constructed in SSE register without loading > from memory". Currently the only one handled is 0, but there is at > least > one more, all 1 bits, which is constructed by > pcmpeqd %xmm, %xmm > Unfortunately there are quite a few places in the patterns that assume > C > means zero, and generate pxor or something like that. What would be > the preferred way to fix this, new constraint or change the existing > patterns? My original plan was to add pcmpeqd by extending the 'C' constraint and the patterns where pxor/xorp? is currently generated unconditionally. This is pretty similar to what we do to i387 constants as well. I never actually got to realizing this (for the scalar FP work I was mostly interested in that time it was not at all that interesting), but I think there is nothing in md file preventing it (or I just missed it when it was added :)...
Honza
