i386: x86 can use x >> y for x >> 32+y [PR36503]

i386: x86 can use x >> y for x >> 32+y [PR36503]

x86 targets mask 32-bit shifts with a 5-bit mask (and 64-bit with 6-bit mask),
so they can use x >> y instead of x >> 32+y.

The optimization converts:

	leal    32(%rsi), %ecx
	sall    %cl, %eax

to:
	sall    %cl, %eax

	PR target/36503

gcc/ChangeLog:

	* config/i386/i386.md (*ashl<mode>3_add):
	New define_insn_and_split pattern.
	(*ashl<mode>3_add_1): Ditto.
	(*<insn><mode>3_add): Ditto.
	(*<insn><mode>3_add_1): Ditto.
	(*ashl<mode>3_sub): Rename from *ashl<mode>3_negcnt.
	(*ashl<mode>3_sub_1): Rename from *ashl<mode>3_negcnt_1.
	(*<insn><mode>3_sub): Rename from *<insn><mode>3_negcnt.
	(*<insn><mode>3_sub_1): Rename from *<insn><mode>3_negcnt_1.

gcc/testsuite/ChangeLog:

	* gcc.target/i386/pr36503-3.c: New test.
	* gcc.target/i386/pr36503-4.c: New test.