Re: [PATCH] PR tree-optimization/83907: Improved memset handling in strlen pass.

[Jeff Law <jeffreyalaw@gmail.com>]

On 2/20/2022 9:51 AM, Roger Sayle wrote:
> This patch implements the missed optimization enhancement PR 83907,
> by handling memset with a constant byte value in tree-ssa's strlen
> optimization pass.  Effectively, this treats memset(dst,'x',3) as
> it would memcpy(dst,"xxx",3).
>
> This patch also includes a tweak to handle_store to address another
> missed optimization observed in the related test case pr83907-2.c.
> The consecutive byte stores to memory get coalesced into a vector
> write of a vector const, but unfortunately tree-ssa-strlen's
> handle_store didn't previously handle the (unusual) case where the
> stored "string" starts with a zero byte but also contains non-zero
> bytes.
>
> This patch has been tested on x86_64-pc-linux-gnu with make bootstrap
> and make -k check with no new failures.  Ok for mainline?
>
>
> 2022-02-20  Roger Sayle  <roger@nextmovesoftware.com>
>
> gcc/ChangeLog
> 	PR tree-optimization/83907
> 	* tree-ssa-strlen.cc (handle_builtin_memset): Record a strinfo
> 	for memset with an constant char value.
> 	(handle_store): Improved handling of stores with a first byte
> 	of zero, but not storing_all_zeros_p.
>
> gcc/testsuite/ChangeLog
> 	PR tree-optimization/83907
> 	* gcc.dg/tree-ssa/pr83907-1.c: New test case.
> 	* gcc.dg/tree-ssa/pr83907-2.c: New test case.
Deferring to stage1.
jeff