This is the mail archive of the
mailing list for the GCC project.
Re: [patch] regcprop fix for PR rtl-optimization/54300
- From: Jeff Law <law at redhat dot com>
- To: Steven Bosscher <stevenb dot gcc at gmail dot com>
- Cc: Richard Earnshaw <rearnsha at arm dot com>, Eric Botcazou <ebotcazou at adacore dot com>, gcc-patches <gcc-patches at gcc dot gnu dot org>
- Date: Tue, 19 Nov 2013 10:48:20 -0700
- Subject: Re: [patch] regcprop fix for PR rtl-optimization/54300
- Authentication-results: sourceware.org; auth=none
- References: <528B9527 dot 2050800 at arm dot com> <CABu31nOddrxBhG3EyPxi=2scYm8xVLbC12NkSvJ8OmDDGOOvBA at mail dot gmail dot com> <528B9F65 dot 6070702 at redhat dot com> <CABu31nMksJFePumou_X=cbdhr3nUJOdDQq6fKrQEq8KrzcJL+w at mail dot gmail dot com>
On 11/19/13 10:32, Steven Bosscher wrote:
Yes. In the GCC3 days it was important for sincos on i386, and on mk68
it used to be important for some of the funnier patterns. Not sure if
it's still useful today, though. Might be worth looking into, just to
avoid the confusion in the future.
I doubt it's changed all that much :-)
Yes. And I'd expect confusion to continue :( Not sure if creating
renaming to capture the actual semantics would help here.
There's been confusion about this before, where people assumed
single_set really means "just one SET in this pattern". (ISTR fixing
gcse.c's hash_scan_rtx for this at some point...?). But that's not the
semantics of single_set.
Seems reasonable for those cases where you have to ensure there really
is just one set.
The proper test for "just one SET" is (!multiple_sets && single_set).
At least, that's how I've always coded it...