[PATCH] target/riscv: rvv: Fix unexpected behavior of vector reduction instructions when vl is 0

[Max Chou]

According to the Vector Reduction Operations section in the RISC-V "V"
Vector Extension spec,
"If vl=0, no operation is performed and the destination register is not
updated."

The vd should be updated when vl is larger than 0.

Signed-off-by: Max Chou <max.chou@sifive.com>
---
 target/riscv/vector_helper.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/target/riscv/vector_helper.c b/target/riscv/vector_helper.c
index 5386e3b97c5..7773df6a7c7 100644
--- a/target/riscv/vector_helper.c
+++ b/target/riscv/vector_helper.c
@@ -4659,7 +4659,9 @@ void HELPER(NAME)(void *vd, void *v0, void *vs1,          
\
         }                                                 \
         s1 = OP(s1, (TD)s2);                              \
     }                                                     \
-    *((TD *)vd + HD(0)) = s1;                             \
+    if (vl > 0) {                                         \
+        *((TD *)vd + HD(0)) = s1;                         \
+    }                                                     \
     env->vstart = 0;                                      \
     /* set tail elements to 1s */                         \
     vext_set_elems_1s(vd, vta, esz, vlenb);               \
@@ -4745,7 +4747,9 @@ void HELPER(NAME)(void *vd, void *v0, void *vs1,          
 \
         }                                                  \
         s1 = OP(s1, (TD)s2, &env->fp_status);              \
     }                                                      \
-    *((TD *)vd + HD(0)) = s1;                              \
+    if (vl > 0) {                                          \
+        *((TD *)vd + HD(0)) = s1;                          \
+    }                                                      \
     env->vstart = 0;                                       \
     /* set tail elements to 1s */                          \
     vext_set_elems_1s(vd, vta, esz, vlenb);                \
-- 
2.34.1