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Re: [patch] Enable -fweb and -frename-registers when unrolling
- From: Paolo Bonzini <paolo dot bonzini at lu dot unisi dot ch>
- To: Zdenek Dvorak <rakdver at atrey dot karlin dot mff dot cuni dot cz>, GCC Patches <gcc-patches at gcc dot gnu dot org>
- Cc: Steven Bosscher <stevenb at suse dot de>
- Date: Tue, 12 Jul 2005 14:18:54 +0200
- Subject: Re: [patch] Enable -fweb and -frename-registers when unrolling
- References: <20050712120135.GA16268@atrey.karlin.mff.cuni.cz>
I hope one day these flags might be enabled by default always, but this
does not seem to be feasible at the moment due to compile time issues.
For -fweb, actually, it was not compile-time issues but performance
issues. The benefit was subsumed by out-of-SSA live range splitting.
Steven Bosscher disabled it.
Rename registers instead is really slow (8% of compile time). And look
out for target bugs caused by rename registers.
However, they are most useful when loops are unrolled, and with
-funroll-loops, the compile time is not that much of a problem, so
perhaps it could be enabled at least then?
You are missing the documentation patch (before somebody else says it!).
-fweb makes debugging impossible, you may want to enable it only if
variable tracking is working on the target (there's already code to do
so, grep for default_debug_hooks).