RISC-V: Avoid more unsplit insns in const expander [PR118832].

RISC-V: Avoid more unsplit insns in const expander [PR118832].

Hi,

in PR118832 we have another instance of the problem already noticed in
PR117878.  We sometimes use e.g. expand_simple_binop for vector
operations like shift or and.  While this is usually OK, it causes
problems when doing it late, e.g. during LRA.

In particular, we might rematerialize a const_vector during LRA, which
then leaves an insn laying around that cannot be split any more if it
requires a pseudo.  Therefore we should only use the split variants
in expand_const_vector.

This patch fixed the issue in the PR and also pre-emptively rewrites two
other spots that might be prone to the same issue.

Regtested on rv64gcv_zvl512b.  As the two other cases don't have a test
(so might not even trigger) I unconditionally enabled them for my testsuite
run.

Regards
 Robin

	PR target/118832

gcc/ChangeLog:

	* config/riscv/riscv-v.cc (expand_const_vector):  Expand as
	vlmax insn during lra.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/autovec/pr118832.c: New test.