strlen: Handle empty constructor as memset for combining with malloc to calloc [PR87900]

This was noticed when turning memset (with constant size) into a store of an empty constructor
but can be reproduced without that.
In this case we have the following IR:
```
  p_3 = __builtin_malloc (4096);
  *p_3 = {};
```

Which we can treat the store as a memset.
So this patch adds the similar optimization as memset/malloc now for malloc/constructor.
This patch is on top of https://gcc.gnu.org/pipermail/gcc-patches/2025-April/681439.html
(it calls allow_memset_malloc_to_calloc but that can be removed if that patch is rejected).

Changes since v1:
* v2: Correctly return false from handle_assign after removing stmt.

Bootstrapped and tested on x86_64-linux-gnu.

	PR tree-optimization/87900

gcc/ChangeLog:

	* tree-ssa-strlen.cc  (strlen_pass::handle_assign): Add RHS argument.
	For empty constructor RHS, see if can combine with a previous malloc into
	a calloc.
	(strlen_pass::check_and_optimize_call): Update call to handle_assign;
	passing NULL_TREE for RHS.
	(strlen_pass::check_and_optimize_stmt): Update call to handle_assign.

gcc/testsuite/ChangeLog:

	* gcc.dg/tree-ssa/calloc-10.c: New test.
	* gcc.dg/tree-ssa/calloc-11.c: New test.
	* gcc.dg/tree-ssa/calloc-12.c: New test.

Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>

0 files changed, 0 insertions, 0 deletions