i386: Optimize popcnt followed by zero/sign extension [PR91824]

i386: Optimize popcnt followed by zero/sign extension [PR91824]

Like any other instruction with 32-bit GPR destination operand in 64-bit
mode, popcntl also clears the upper 32 bits of the register (and other bits
too, it can return only 0 to 32 inclusive).

During combine, the zero or sign extensions of it show up as paradoxical
subreg of the popcount & 63, there 63 is the smallest power of two - 1 mask
that can represent all the 0 to 32 inclusive values.

2020-01-30  Jakub Jelinek  <jakub@redhat.com>

	PR target/91824
	* config/i386/i386.md (*popcountsi2_zext): New define_insn_and_split.
	(*popcountsi2_zext_falsedep): New define_insn.

	* gcc.target/i386/pr91824-1.c: New test.