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 <ro...@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
