Re: [PATCH] tree-optimization/101573 - improve uninit warning at -O0

[Jeff Law <jeffreyalaw@gmail.com>]

On 7/22/2021 6:34 AM, Richard Biener wrote:
> We can improve uninit warnings from the early pass by looking
> at PHI arguments on fallthru edges that are uninitialized and
> have uses that are before a possible loop exit.  This catches
> some cases earlier that we'd only warn in a more confusing
> way after early inlining as seen by testcase adjustments.
>
> It introduces
>
> FAIL: gcc.dg/uninit-23.c (test for excess errors)
>
> where we additionally warn
>
> gcc.dg/uninit-23.c:21:13: warning: 't4' is used uninitialized [-Wuninitialized]
>
> which I think is OK even if it's not obvious that the new
> warning is an improvement when you look at the obvious source.
>
> Somehow for all cases I never get the `'foo' was declared here`
> notes, I didn't dig why that happens but it's odd.
>
> Bootstrapped and tested on x86_64-unknown-linux-gnu.
>
> Any comments?
>
> Thanks,
> Richard.
>
> 2021-07-22  Richard Biener  <rguenther@suse.de>
>
> 	PR tree-optimization/101573
> 	* tree-ssa-uninit.c (warn_uninitialized_vars): Look at
> 	uninitialized PHI arg defs in some constrained cases.
> 	(execute_early_warn_uninitialized): Calculate dominators.
>
> 	* gcc.dg/uninit-pr101573.c: New testcase.
> 	* gcc.dg/uninit-15-O0.c: Adjust.
> 	* gcc.dg/uninit-15.c: Likewise.
> 	* gcc.dg/uninit-23.c: Likewise.
> 	* c-c++-common/uninit-17.c: Likewise.
OK.  Like Martin I think the new code in a function would be easier to 
read.  So if you could factor the bits into a new function it'd be 
appreciated.

I wouldn't be terribly surprised if we find additional fallout on other 
targets, but we can fault in those fixes.

Jeff