i386: Fix FAIL of gcc.target/i386/pr91681-1.c

The recent change in TImode parameter passing on x86_64 results in the
FAIL of pr91681-1.c.  The issue is that with the extra flexibility,
the combine pass is now spoilt for choice between using either the
*add<dwi>3_doubleword_concat or the *add<dwi>3_doubleword_zext
patterns, when one operand is a *concat and the other is a zero_extend.
The solution proposed below is provide an *add<dwi>3_doubleword_concat_zext
define_insn_and_split, that can benefit both from the register allocation
of *concat, and still avoid the xor normally required by zero extension.

I'm investigating a follow-up refinement to improve register allocation
further by avoiding the early clobber in the =&r, and handling (custom)
reloads explicitly, but this piece resolves the testcase failure.

2023-07-12  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
	PR target/91681
	* config/i386/i386.md (*add<dwi>3_doubleword_concat_zext): New
	define_insn_and_split derived from *add<dwi>3_doubleword_concat
	and *add<dwi>3_doubleword_zext.

0 files changed, 0 insertions, 0 deletions