[PATCH v3] match.pd: popcount(X & -X) -> -X != 0 [PR102486]

[PATCH v3] match.pd: popcount(X & -X) -> -X != 0 [PR102486]

The initial idea of this optimization was to reduce it to "X != 0",
checking for either X being an unsigned or a truncating conversion.
Then we discussed reducing it to "(X & -X) != 0" instead. This form
would avoid the potential trapping problems (like -ftrapv) that might
happen in case X is not an unsigned type.

Then, as suggested by Roger Sayle in bugzilla, we could reduce to just
"-X != 0". Keeping the negated value in the pattern preserves any trapping
or UBs to be handled by other match.pd patterns that are more able to do
the conversion to "X != 0" when applicable. This would also spare us from
a TYPE_UNSIGNED check.

	PR tree-optimization/102486

gcc/ChangeLog:

	* match.pd (`popcount (X & -X) -> -X != 0`): New pattern.

gcc/testsuite/ChangeLog:

	* gcc.dg/tree-ssa/pr102486.c: New test.

Signed-off-by: Daniel Barboza <daniel.barboza@oss.qualcomm.com>