middle-end: PR tree-optimization/21137: STRIP_NOPS avoids missed optimization.

middle-end: PR tree-optimization/21137: STRIP_NOPS avoids missed optimization.

PR tree-optimization/21137 is now an old enhancement request pointing out
that an optimization I added back in 2006, to optimize "((x>>31)&64) != 0"
as "x < 0", doesn't fire in the presence of unanticipated type conversions.
The fix is to call STRIP_NOPS at the appropriate point.

2020-08-25  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
	PR tree-optimization/21137
	* fold-const.c (fold_binary_loc) [NE_EXPR/EQ_EXPR]: Call
	STRIP_NOPS when checking whether to simplify ((x>>C1)&C2) != 0.

gcc/testsuite/ChangeLog
	PR tree-optimization/21137
	* gcc.dg/pr21137.c: New test.