i386: Fix up @xorsign<mode>3_1 [PR102224]

i386: Fix up @xorsign<mode>3_1 [PR102224]

As the testcase shows, we miscompile @xorsign<mode>3_1 if both input
operands are in the same register, because the splitter overwrites op1
before with op1 & mask before using op0.

For dest = xorsign op0, op0 we can actually simplify it from
dest = (op0 & mask) ^ op0 to dest = op0 & ~mask (aka abs).

The expander change is an optimization improvement, if we at expansion
time know it is xorsign op0, op0, we can emit abs right away and get better
code through that.

The @xorsign<mode>3_1 is a fix for the case where xorsign wouldn't be known
to have same operands during expansion, but during RTL optimizations they
would appear.  We need to use earlyclobber, we require dest and op1 to be
the same but op0 must be different because we overwrite
op1 first.

2021-09-08  Jakub Jelinek  <jakub@redhat.com>

	PR target/102224
	* config/i386/i386.md (xorsign<mode>3): If operands[1] is equal to
	operands[2], emit abs<mode>2 instead.
	(@xorsign<mode>3_1): Add early-clobber for output operand.

	* gcc.dg/pr102224.c: New test.
	* gcc.target/i386/avx-pr102224.c: New test.

(cherry picked from commit a7b626d98a9a821ffb33466818d6aa86cac1d6fd)