This is the mail archive of the mailing list for the GCC project.

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

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

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().



PR tree-optimization/86042 - missing strlen optimization after second strcpy


	PR tree-optimization/86042
	* tree-ssa-strlen.c (handle_builtin_memcpy): Handle strict overlaps.
	(get_string_cst_length): Rename...
	(get_min_string_length): this.  Add argument.
	(handle_char_store): Extend to handle multi-character stores by
	* tree.c (initializer_zerop): Use new argument.  Handle MEM_REF.
	* tree.h (initializer_zerop): Add argument.


	PR tree-optimization/86042
	* gcc.dg/strlenopt-44.c: New test.

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.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]