phiopt/cselim: Improve cselim-limited to commonalize all stores [PR122083]

phiopt/cselim: Improve cselim-limited to commonalize all stores [PR122083]

cselim (and the phiopt's cselim-limited) can commonalize a single
store which makes this too limited in some/many cases. Instead let's
commonalize all trailing stores as much as possible (only in the same
order).
The change is smallish, basically the restriction on being the only store
is removed from single_trailing_store_in_bb (renamed too). And also
looping to remove all of the trailing stores instead of just doing one for
the pass.

Note sink will do the same optimization so doing it earlier seems like a good
idea because it improve change inlining size estimates.
For an example with this change, early inlining can happen for min_cmp<long int>
in g++.dg/opt/pr122083-1.C now; that avoids a -Wnonnull warning as the memcmp with
the null argument is optimized early. It can also catch some min in phiopt1 in some
cases.

Bootstrapped and tested on x86_64-linux-gnu.

Changes since v1:
* v2: For !flag_expensive_optimizations, handle the only store rather than just the last
      store.

	PR tree-optimization/122083

gcc/ChangeLog:

	* tree-ssa-phiopt.cc (single_trailing_store_in_bb): Rename to ...
	(trailing_store_in_bb): This and take new argument to check for
	only store.
	(cond_if_else_store_replacement_limited): Update to use
	trailing_store_in_bb.
	(cond_if_else_store_replacement): Loop until
	cond_if_else_store_replacement_limited returns false.
	(pass_phiopt::execute): Instead of calling cond_if_else_store_replacement_limited
	once, also loop on it.

gcc/testsuite/ChangeLog:

	* gcc.dg/tree-ssa/ssa-pre-19.c: Disable phiopt and cselim.
	* g++.dg/opt/pr122083-1.C: New test.
	* gcc.dg/tree-ssa/cselim-1.c: New test.
	* gcc.dg/tree-ssa/cselim-2.c: New test.

Signed-off-by: Andrew Pinski <andrew.pinski@oss.qualcomm.com>