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Re: Use-and-clobber insns and some ancient combine.c code
- From: kenner at vlsi1 dot ultra dot nyu dot edu (Richard Kenner)
- To: weigand at i1 dot informatik dot uni-erlangen dot de
- Cc: gcc at gcc dot gnu dot org
- Date: Thu, 17 Jun 04 15:57:07 EDT
- Subject: Re: Use-and-clobber insns and some ancient combine.c code
Your change added a *second* test, for substitution of
(set (reg Y) (...(some use of reg X)...))
(parallel [ ...(some use of reg Y)... (clobber (reg X)) ...])
It this *this* check I don't understand.
I think it's indeed the earlyclobber issue: you can't be sure that the
clobber will happen before X is read.