http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27468
--- Comment #5 from Uros Bizjak <ubizjak at gmail dot com> 2011-12-22 10:25:10 UTC --- With proposed patch to enable REE pass, we still generate: 0000000000000000 <f5>: 0: 20 05 f0 43 negq a0,v0 4: c0 08 10 46 cmovge a0,a0,v0 8: 00 00 e0 43 sextl v0,v0 c: 01 80 fa 6b ret However, we need a sign extend somewhere, and in above case, we apply sign extension to the result, where Compaq C applies extension to the arguments of cmove. These sequences are equivalent an all aspects. FYI: Proposed "optimal" f5 sequence is wrong. Since cmov always operates on the whole DImode register, garbage in bits 31+ of a0 can pass unmodified to the function result. Compaq C is correct to produce: 0000000000000000 <f5>: 0: 10 00 f0 43 sextl a0,a0 4: 20 01 f0 43 negl a0,v0 8: c0 08 10 46 cmovge a0,a0,v0 c: 00 00 fe 2f unop 10: 01 80 fa 6b ret but this is effectively no different than gcc sequence above.
