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Re: RFA: New pass to delete unexecutable paths in the CFG
- From: Jakub Jelinek <jakub at redhat dot com>
- To: Jeff Law <law at redhat dot com>
- Cc: gcc-patches <gcc-patches at gcc dot gnu dot org>
- Date: Mon, 7 Nov 2011 11:07:00 +0100
- Subject: Re: RFA: New pass to delete unexecutable paths in the CFG
- References: <4EB7AAF6.6060702@redhat.com>
- Reply-to: Jakub Jelinek <jakub at redhat dot com>
On Mon, Nov 07, 2011 at 02:55:02AM -0700, Jeff Law wrote:
> [ Working virtually from Hawaii tonight... :-) ]
;)
> You might legitimately wonder how often this triggers. A GCC 4.6.0
> checking-enabled compiler sees a .64% codesize improvement from this
> optimization. That's an awful lot of unexecutable code. The NULL
> references come from the VEC implementation and a variety of other
> sources.
I'd say it is a good idea, though I wonder if the gate shouldn't
also use && flag_delete_null_pointer_checks or at least if the default
for this new option shouldn't be based on flag_delete_null_pointer_checks.
-fno-delete-null-pointer-checks is documented for quite some time as an option
which allows NULL pointer dereferences (and AFAIK AVR uses it) and
people who use that option will most likely want to disable this
optimization too.
Jakub