target/riscv/vector_helper.c: optimize loops in ldst helpers

Change the for loops in ldst helpers to do a single increment in the
counter, and assign it env->vstart, to avoid re-reading from vstart
every time.

Suggested-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-ID: <20240314175704.478276-11-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
(cherry picked from commit 0a11629)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

target/riscv/vector_helper.c

@@ -198,7 +198,7 @@ vext_ldst_stride(void *vd, void *v0, target_ulong base,
 
     VSTART_CHECK_EARLY_EXIT(env);
 
-    for (i = env->vstart; i < env->vl; i++, env->vstart++) {
+    for (i = env->vstart; i < env->vl; env->vstart = ++i) {
         k = 0;
         while (k < nf) {
             if (!vm && !vext_elem_mask(v0, i)) {
@@ -266,7 +266,7 @@ vext_ldst_us(void *vd, target_ulong base, CPURISCVState *env, uint32_t desc,
     VSTART_CHECK_EARLY_EXIT(env);
 
     /* load bytes from guest memory */
-    for (i = env->vstart; i < evl; i++, env->vstart++) {
+    for (i = env->vstart; i < evl; env->vstart = ++i) {
         k = 0;
         while (k < nf) {
             target_ulong addr = base + ((i * nf + k) << log2_esz);
@@ -382,7 +382,7 @@ vext_ldst_index(void *vd, void *v0, target_ulong base,
     VSTART_CHECK_EARLY_EXIT(env);
 
     /* load bytes from guest memory */
-    for (i = env->vstart; i < env->vl; i++, env->vstart++) {
+    for (i = env->vstart; i < env->vl; env->vstart = ++i) {
         k = 0;
         while (k < nf) {
             if (!vm && !vext_elem_mask(v0, i)) {