i386: Improve workaround for PR82524 LRA limitation [PR85730]

As explained in PR82524, LRA is not able to reload strict_low_part inout
operand with matched input operand. The patch introduces a workaround,
where we allow LRA to generate an instruction with non-matched input operand
which is split post reload to an instruction that inserts non-matched input
operand to an inout operand and the instruction that uses matched operand.

The generated code improves from:

        movsbl  %dil, %edx
        movl    %edi, %eax
        sall    $3, %edx
        movb    %dl, %al

to:

        movl    %edi, %eax
        movb    %dil, %al
        salb    $3, %al

which is still not optimal, but the code is one instruction shorter and
does not use a temporary register.

2021-10-12  Uroš Bizjak  <ubizjak@gmail.com>

gcc/
	PR target/85730
	PR target/82524
	* config/i386/i386.md (*add<mode>_1_slp): Rewrite as
	define_insn_and_split pattern.  Add alternative 1 and split it
	post reload to insert operand 1 into the low part of operand 0.
	(*sub<mode>_1_slp): Ditto.
	(*and<mode>_1_slp): Ditto.
	(*<any_or:code><mode>_1_slp): Ditto.
	(*ashl<mode>3_1_slp): Ditto.
	(*<any_shiftrt:insn><mode>3_1_slp): Ditto.
	(*<any_rotate:insn><mode>3_1_slp): Ditto.
	(*neg<mode>_1_slp): New insn_and_split pattern.
	(*one_cmpl<mode>_1_slp): Ditto.

gcc/testsuite/
	PR target/85730
	PR target/82524
	* gcc.target/i386/pr85730.c: New test.