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Re: [tree-ssa] New regressions as of 2003-11-04
- From: law at redhat dot com
- To: Jan Hubicka <jh at suse dot cz>
- Cc: Andrew MacLeod <amacleod at redhat dot com>, Diego Novillo <dnovillo at redhat dot com>, Zdenek Dvorak <rakdver at atrey dot karlin dot mff dot cuni dot cz>, Daniel Berlin <dberlin at dberlin dot org>, gcc mailing list <gcc at gcc dot gnu dot org>
- Date: Mon, 10 Nov 2003 12:00:08 -0700
- Subject: Re: [tree-ssa] New regressions as of 2003-11-04
- Reply-to: law at redhat dot com
In message <20031105145858.GS13705@kam.mff.cuni.cz>, Jan Hubicka writes:
>We can do it that way, but the function should be mostly NOOP now.
>cleanup_cfg+dead code removal should've caught all cases previously.
It's definitely not a NOP. Have you actually compared the tree dumps
with and without this pass?
Also don't forget it's now used before we build the CFG to clean up obviously
useless junk.
>The point is that we *want* to create temporary registers so unless
>there is good reason to do so, we don't want single register to be set
>two times. That confuses RTL.
More correctly, having a register set multiple times can inhibit certain
optimizations. Just as an example, if a register is set more than once
we're a lot less aggressive about marking it as a pointer.
jeff