tree-optimization/105517 - avoid offset truncation during VN

tree-optimization/105517 - avoid offset truncation during VN

When value-numbering an address expression like
&p_74(D)->a1x[4294967295].a1; we are accumulating the byte offset
in an 64bit integer.  When later exploiting the duality between
that and a POINTER_PLUS_EXPR we should avoid truncating that
offset to fit in the target specific sizetype.  While such
overflows are generally undefined behavior, exploiting this
may leads to spurious missing diagnostics.

2022-05-09  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/105517
	* tree-ssa-sccvn.cc (vn_reference_lookup): Make sure the accumulated
	offset can be represented in the POINTER_PLUS_EXPR IL.
	(vn_reference_insert): Likewise.
	* poly-int.h (sext_hwi): Add poly version of sext_hwi.