Re: [PATCH] avoid bogus -Wstringop-truncation when inlining (PR 84480)

[Martin Sebor <msebor at gmail dot com>]

On 02/21/2018 07:53 PM, Jeff Law wrote:
> On 02/21/2018 02:19 PM, Martin Sebor wrote:
> > The attached patch eliminates -Wstringop-truncation false
> > positives reported in bug 84480 - bogus -Wstringop-truncation
> > despite assignment with an inlined string literal.  It does
> > that by delegating early strncpy checks during folding to
> > the same machinery in tree-ssa-strlen that looks for a NUL
> > assignment to the destination the next statement.
> >
> > The patch also adds inlining context to the warnings via
> > the %G directive.
> >
> > Tested on x86_64-linux with no regressions.
> >
> > Martin
> >
> > gcc-84480.diff
> >
> >
> > PR tree-optimization/84480 - bogus -Wstringop-truncation despite assignment with an inlined string literal
> >
> > gcc/ChangeLog:
> >
> > 	PR tree-optimization/84480
> > 	* gimple-fold.c (gimple_fold_builtin_strcpy): Move warnings
> > 	to maybe_diag_stxncpy_trunc.  Call it.
> > 	* tree-ssa-strlen.c (maybe_diag_stxncpy_trunc): Integrate warnings
> > 	from gimple_fold_builtin_strcpy.  Print inlining stack.
> > 	(handle_builtin_stxncpy): Print inlining stack.
> > 	* tree-ssa-strlen.h (maybe_diag_stxncpy_trunc): Declare.
> >
> > gcc/testsuite/ChangeLog:
> >
> > 	PR tree-optimization/84480
> > 	* c-c++-common/Wstringop-truncation.c: Adjust text of expected warnings.
> > 	* g++.dg/warn/Wstringop-truncation-1.C: New test.
> In general our guidelines are that the users of a .h file should include
> any dependencies rather than having the .h file itself include other .h
> files (Now that we've detangled the header files we may want to revisit
> that guideline, but that's not a gcc-8 item).
>
> It looks like gimple-fold.c and tree-ssa-strlen.c already have the
> prereqs.  So in theory you should be able to just remove the bogus
> #includes from tree-ssa-strlen.h.

Done.

> In general we want to avoid adding more warnings to folding code.  But I
> think the argument here is that we're already trying to warn within the
> folder and just doing a poor job -- so we're removing that
> implementation and delegating the warning to a better implementation.
> Right?

Exactly.

> So I think you just need to remove the bogus #includes from
> tree-ssa-strlen and this is OK.

Thanks.  Committed in r257910.

Martin