commit 7ac3e69e311351b70407d7f87a0169c4d463e57b
author Richard Biener <rguenther@suse.de> Mon Jan 30 09:25:23 2023 +0100
committer Richard Biener <rguenther@suse.de> Mon Jan 30 10:50:52 2023 +0100
tree 3435a90ad55baa9432ac21daaa9f636b25629661
parent 3cd08f7168c196d7a481b9ed9f4289fd1f14eea8

tree-optimization/108574 - wrong-code with PRE PHI node processing

The PR108523 was too optimistic in replacing the same value with
an equivalence from a possibly not taken edge.  The following
rectifies this and instead refrains from using the equivalence in
the problematic cases.

	PR tree-optimization/108574
	* tree-ssa-sccvn.cc (visit_phi): Instead of swapping
	sameval and def, ignore the equivalence if there's the
	danger of oscillating between two values.

	* gcc.dg/torture/pr108574-1.c: New testcase.
	* gcc.dg/torture/pr108574-2.c: Likewise.
	* gcc.dg/torture/pr108574-3.c: Likewise.