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Re: Resend: reorder conditionals in i386.md
- To: Zack Weinberg <zackw at panix dot com>
- Subject: Re: Resend: reorder conditionals in i386.md
- From: Robert Lipe <robertlipe at usa dot net>
- Date: Tue, 7 Aug 2001 13:45:41 -0500
- Cc: gcc-patches at gcc dot gnu dot org
- References: <20010807141831.C17452@panix.com>
Zack said:
> rearranges a lot of guard expressions in i386.md such that constant
> sub- expressions such as "TARGET_64BIT" appear first. When the
> subexpression is compile-time false, the optimizer can then discard
> the entire expression
Isn't that pandering to a weak optimizer?
If we really can do something different with
if (0 && TARGET_80386)
than we can with
if (TARGET_80386 && 0)
(where the '0' comes from cpp in specific cases and isn't, of course,
quite so obvious as I'm making it sound) haven't we left an optimization
on the table?
Interestingly, if the '0' is a const int expression, we don't appear to
know that these are as unreachable as if they're a zero right in the
expression...
RJL