tree-optimization/100051 - disambiguate access size vs decl

tree-optimization/100051 - disambiguate access size vs decl

This adds disambiguation of the access size vs. the decl size
in the pointer based vs. decl based disambiguator.  We have
a TBAA based check like this already but that's fend off when
seeing alias-sets of zero or when -fno-strict-aliasing is in
effect.  Also the perceived dynamic type could be smaller than
the actual access.

2021-04-13  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/100051
	* tree-ssa-alias.c (indirect_ref_may_alias_decl_p): Add
	disambiguator based on access size vs. decl size.

	* gcc.dg/tree-ssa/ssa-fre-92.c: New testcase.