tree-optimization/92645 - avoid harmful early BIT_FIELD_REF canonicalization

tree-optimization/92645 - avoid harmful early BIT_FIELD_REF canonicalization

This avoids canonicalizing BIT_FIELD_REF <T1> (a, <sz>, 0) to
(T1)a on integer typed a.  This confuses the vectorizer SLP matching.

With this delayed to after vector lowering the testcase in PR92645
from Skia is now finally optimized to reasonable assembly.

2021-01-13  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/92645
	* match.pd (BIT_FIELD_REF to conversion): Delay canonicalization
	until after vector lowering.

	* gcc.target/i386/pr92645-7.c: New testcase.
	* gcc.dg/tree-ssa/ssa-fre-54.c: Adjust.
	* gcc.dg/pr69047.c: Likewise.