Re: [PATCH RFC] c-family: -Wsequence-point and COMPONENT_REF [PR107163]

[Jakub Jelinek <jakub@redhat.com>]

On Fri, Mar 24, 2023 at 06:11:44PM -0400, Jason Merrill wrote:
> > When we touch this for COMPONENT_REF, shouldn't we then handle it as
> > unary given that the second operand is FIELD_DECL and third/fourth
> > will likely be NULL and even if not, aren't user expressions that should be
> > inspected?
> > So, instead of doing this do:
> >      case COMPONENT_REF:
> >        x = TREE_OPERAND (x, 0);
> >        writer = 0;
> >        goto restart;
> > ?
> 
> Is clearing 'writer' what we want, since an access to COMPONENT_REF is an
> access to (a subobject of) its op0?

I've just mindlessly copied the unary op case.
writer is set for pre/post increments and lhs of MODIFY_EXPR, and it is
true that VIEW_CONVERT_EXPR doesn't clear it, but e.g. ARRAY_REF clears it
for all operands.

> Currently with the fix it takes <1s while gcc12 takes ~80s.

Perfect.

> 	PR c++/107163
> 
> gcc/c-family/ChangeLog:
> 
> 	* c-common.cc (verify_tree): Don't use sequenced handling
> 	for COMPONENT_REF.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/template/recurse5.C: New test.

LGTM, thanks.  Maybe the testcase would be better as
warn/Wsequence-point-5.C, dunno.

	Jakub