re PR target/88152 (optimize SSE & AVX char compares with subsequent movmskb)

re PR target/88152 (optimize SSE & AVX char compares with subsequent movmskb)

	PR target/88152
	* tree.h (build_uniform_cst, uniform_integer_cst_p): Declare.
	* tree.c (build_uniform_cst, uniform_integer_cst_p): New functions.
	* match.pd (define_predicates): Add uniform_integer_cst_p.
	(cmp @0 INTEGER_CST@1, cmp (convert?@2 @0) INTEGER_CST@1): Adjust
	so that it works also for vector comparisons with uniform constants
	with INTEGER_CST element.

	* g++.dg/tree-ssa/pr88152-1.C: New test.
	* g++.dg/tree-ssa/pr88152-2.C: New test.

From-SVN: r266620