Messages in this thread | | | Date | Wed, 09 Apr 2008 15:33:38 -0700 | From | "H. Peter Anvin" <> | Subject | Re: [patch 13/17] Immediate Values - x86 Optimization |
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Mathieu Desnoyers wrote: > * H. Peter Anvin (hpa@zytor.com) wrote: >> Mathieu Desnoyers wrote: >>> Ok, so the most flexible solution that I see, that should fit for both >>> x86 and x86_64 would be : >>> 1 byte : "=q" : "a", "b", "c", or "d" register for the i386. For >>> x86-64 it is equivalent to "r" class (for 8-bit >>> instructions that do not use upper halves). >>> 2, 4, 8 bytes : "=r" : A register operand is allowed provided that it is >>> in a >>> general register. >> Any reason to keep carrying this completely misleading comment chunk still? >> >> -hpa > > This comment explains why I use the =q constraint for the 1 bytes > immediate value. It makes sure we use an instruction with 1-byte opcode, > without REX.R prefix, on x86_64.
No, it doesn't. That would be "=Q".
-hpa
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