s390: Use match_scratch instead of scratch in define_split [PR119834]

s390: Use match_scratch instead of scratch in define_split [PR119834]

The following testcase ICEs since r15-1579 (addition of late combiner),
because *clrmem_short can't be split.
The problem is that the define_insn uses
   (use (match_operand 1 "nonmemory_operand" "n,a,a,a"))
   (use (match_operand 2 "immediate_operand" "X,R,X,X"))
   (clobber (match_scratch:P 3 "=X,X,X,&a"))
and define_split assumed that if operands[1] is const_int_operand,
match_scratch will be always scratch, and it will be reg only if
it was the last alternative where operands[1] is a reg.
The pattern doesn't guarantee it though, of course RA will not try to
uselessly assign a reg there if it is not needed, but during RA
on the testcase below we match the last alternative, but then comes
late combiner and propagates const_int 3 into operands[1].  And that
matches fine, match_scratch matches either scratch or reg and the constraint
in that case is X for the first variant, so still just fine.  But we won't
split that because the splitters only expect scratch.

The following patch fixes it by using match_scratch instead of scratch,
so that it accepts either.

2025-04-17  Jakub Jelinek  <jakub@redhat.com>

	PR target/119834
	* config/s390/s390.md (define_split after *cpymem_short): Use
	(clobber (match_scratch N)) instead of (clobber (scratch)).  Use
	(match_dup 4) and operands[4] instead of (match_dup 3) and operands[3]
	in the last of those.
	(define_split after *clrmem_short): Use (clobber (match_scratch N))
	instead of (clobber (scratch)).
	(define_split after *cmpmem_short): Likewise.

	* g++.target/s390/pr119834.C: New test.