match.pd: Add some __builtin_ctz (x) cmp cst simplifications [PR95527]

match.pd: Add some __builtin_ctz (x) cmp cst simplifications [PR95527]

This patch adds some ctz simplifications (e.g. ctz (x) >= 3 can be done by
testing if the low 3 bits are zero, etc.).

In addition, I've noticed that in the CLZ case, the
 #ifdef CLZ_DEFINED_VALUE_AT_ZERO don't really work as intended, they
are evaluated during genmatch and the macro is not defined then
(but, because of the missing tm.h includes it isn't defined in
gimple-match.c or generic-match.c either).  And when tm.h is included,
defaults.h is included which defines a fallback version of that macro.

For GCC 12, I wonder if it wouldn't be better to say in addition to __builtin_c[lt]z*
is always UB at zero that it would be undefined for .C[LT]Z ifn too if it
has just one operand and use a second operand to be the constant we expect
at zero.

2021-04-27  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/95527
	* generic-match-head.c: Include tm.h.
	* gimple-match-head.c: Include tm.h.
	* match.pd (CLZ == INTEGER_CST): Don't use
	#ifdef CLZ_DEFINED_VALUE_AT_ZERO, only test CLZ_DEFINED_VALUE_AT_ZERO
	if clz == CFN_CLZ.  Add missing val declaration.
	(CTZ cmp CST): New simplifications.

	* gcc.dg/tree-ssa/pr95527-2.c: New test.