Re: RFA: New pass to delete unexecutable paths in the CFG

[Jeff Law <law@redhat.com>]

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On 11/07/11 03:07, Jakub Jelinek wrote:
> 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.
Yea, I'd been back and forth on this too -- I don't like gating on the
null-pointer-check flag, but I agree that folks using
- -fno-delete-null-... probably aren't going to want the new
optimization either.

I'll put on my thinking cap and see if I can come up with a good name
that encompasses both classes of optimization without getting overly
broad.

jeff
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