Re: [PATCH] enhance strlen to understand MEM_REF and partial overlaps (PR 86042, 86043)

[Martin Sebor <msebor at gmail dot com>]

On 06/29/2018 11:05 AM, Jeff Law wrote:
> On 06/07/2018 09:57 AM, Martin Sebor wrote:
> > The attached patch enhances the strlen pass to more consistently
> > deal with MEM_REF assignments (PR 86042) and to track string
> > lengths across calls to memcpy that overwrite parts of a string
> > with sequences of non-nul characters (PR 86043).
> >
> > Fixes for both bugs rely on changes to the same code so I chose
> > to include them in the same patch.
> >
> > To fix PR 86042 the patch extends handle_char_store() to deal with
> > more forms of multi-character assignments from MEM_REF (originally
> > introduced in r256180).  To handle assignments from strings of
> > multiple nuls the patch also extends the initializer_zerop()
> > function to understand MEM_REFs of the form:
> >
> >    MEM[(char * {ref-all})&a] = MEM[(char * {ref-all})"..."];
> >
> > The solution for PR 86043 consists of two parts: the extension
> > above which lets handle_char_store() recognize assignments of
> > sequences of non-null characters that overwrite some portion of
> > the leading non-zero characters in the destination and avoid
> > discarding the destination information, and a similar extension
> > to handle_builtin_memcpy().
> >
> > Martin
> >
> > gcc-86042.diff
> >
> >
> > PR tree-optimization/86042 - missing strlen optimization after second strcpy
> >
> > gcc/ChangeLog:
> >
> > 	PR tree-optimization/86042
> > 	* tree-ssa-strlen.c (handle_builtin_memcpy): Handle strict overlaps.
> > 	(get_string_cst_length): Rename...
> > 	(get_min_string_length): ...to this.  Add argument.
> > 	(handle_char_store): Extend to handle multi-character stores by
> > 	MEM_REF.
> > 	* tree.c (initializer_zerop): Use new argument.  Handle MEM_REF.
> > 	* tree.h (initializer_zerop): Add argument.
> >
> > gcc/testsuite/ChangeLog:
> >
> > 	PR tree-optimization/86042
> > 	* gcc.dg/strlenopt-44.c: New test.
> OK.

I missed your approval and didn't get to committing the patch
until today.  While retesting it on top of fresh trunk I noticed
a few test failures due to other recent strlen changes.  I made
adjustments to the patch to avoid most of them and opened bug
86688 for one that I think needs a separate code change and
xfailed the test cases until the bug gets resolved.

Martin