Delayed warning

Delayed warning

[Thomas Koenig]

Hi!

Is there a way to mark a TREE statement (or a variable) so that
a warning is issued at a later stage if the statement has not been
removed in the meantime?

I am thinking, for example, of Fortran's -Warray-temporaries, which
issues a warning in the front end even though the whole temporary
array may be optimized away later.  We could, for example, mark
a call to malloc in such a way.

Regards

	Thomas

Re: Delayed warning

[Jeff Law]

On 4/29/19 8:24 AM, Thomas Koenig wrote:
> Hi!
> 
> Is there a way to mark a TREE statement (or a variable) so that
> a warning is issued at a later stage if the statement has not been
> removed in the meantime?
> 
> I am thinking, for example, of Fortran's -Warray-temporaries, which
> issues a warning in the front end even though the whole temporary
> array may be optimized away later.  We could, for example, mark
> a call to malloc in such a way.
I'm not aware of one, but I recently suggested the concept of
__builtin_warning which would allow us to effectively delay a warning.

The goal was to have the warning explicitly in the IL so that if the
path to the warning was later determined infeasible the warning would
just get removed by the standard unreachable code elimination optimization.

This would allow us to avoid false positives due to the IL not being
well enough optimized at the point where we discover something is
potentially amiss.

Jeff

Re: Delayed warning

[Marek Polacek]

On Mon, Apr 29, 2019 at 08:39:57AM -0600, Jeff Law wrote:
> On 4/29/19 8:24 AM, Thomas Koenig wrote:
> > Hi!
> > 
> > Is there a way to mark a TREE statement (or a variable) so that
> > a warning is issued at a later stage if the statement has not been
> > removed in the meantime?
> > 
> > I am thinking, for example, of Fortran's -Warray-temporaries, which
> > issues a warning in the front end even though the whole temporary
> > array may be optimized away later.  We could, for example, mark
> > a call to malloc in such a way.
> I'm not aware of one, but I recently suggested the concept of
> __builtin_warning which would allow us to effectively delay a warning.
> 
> The goal was to have the warning explicitly in the IL so that if the
> path to the warning was later determined infeasible the warning would
> just get removed by the standard unreachable code elimination optimization.
> 
> This would allow us to avoid false positives due to the IL not being
> well enough optimized at the point where we discover something is
> potentially amiss.

FYI, I also raised the idea of delayed warnings in the C FE some time ago:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68193#c3

Marek