target/riscv: always clear vstart for ldst_whole insns

target/riscv: always clear vstart for ldst_whole insns

Commit 8ff8ac6329 added a conditional to guard the vext_ldst_whole()
helper if vstart >= evl. But by skipping the helper we're also not
setting vstart = 0 at the end of the insns, which is incorrect.

We'll move the conditional to vext_ldst_whole(), following in line with
the removal of all brconds vstart >= vl that the next patch will do. The
idea is to make the helpers responsible for their own vstart management.

Fix ldst_whole isns by:

- remove the brcond that skips the helper if vstart is >= evl;

- vext_ldst_whole() now does an early exit with the same check, where
  evl = (vlenb * nf) >> log2_esz, but the early exit will also clear
  vstart.

The 'width' param is now unneeded in ldst_whole_trans() and is also
removed. It was used for the evl calculation for the brcond and has no
other use now.  The 'width' is reflected in vext_ldst_whole() via
log2_esz, which is encoded by GEN_VEXT_LD_WHOLE() as
"ctzl(sizeof(ETYPE))".

Suggested-by: Max Chou <max.chou@sifive.com>
Fixes: 8ff8ac6329 ("target/riscv: rvv: Add missing early exit condition for whole register load/store")
Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Max Chou <max.chou@sifive.com>
Message-ID: <20240314175704.478276-6-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>