make sure vstart is zero when instruction early return

model/extensions/V/vext_fp_red_insts.sail

@@ -66,7 +66,7 @@ function process_rfvv_single(funct6, vm, vs2, vs1, vd, num_elem_vs, SEW, LMUL_po
   write_single_element(SEW, 0, vd, sum);
   // other elements in vd are treated as tail elements, currently remain unchanged
   // TODO: configuration support for agnostic behavior
-  set_vstart(zeros());
+  // illegal_fp_reduction checks vstart == 0, and raises illegal-instruction otherwise.
   RETIRE_SUCCESS
 }
 
@@ -106,7 +106,7 @@ function process_rfvv_widening_reduction(funct6, vm, vs2, vs1, vd, num_elem_vs,
   write_single_element(SEW_widen, 0, vd, sum);
   // other elements in vd are treated as tail elements, currently remain unchanged
   // TODO: configuration support for agnostic behavior
-  set_vstart(zeros());
+  // illegal_fp_widening_reduction checks vstart == 0, and raises illegal-instruction otherwise.
   RETIRE_SUCCESS
 }
 

model/extensions/V/vext_red_insts.sail

@@ -64,7 +64,7 @@ function clause execute(RIVVTYPE(funct6, vm, vs2, vs1, vd)) = {
   write_single_element(SEW_widen, 0, vd, sum);
   // other elements in vd are treated as tail elements, currently remain unchanged
   // TODO: configuration support for agnostic behavior
-  set_vstart(zeros());
+  // illegal_widening_reduction checks vstart == 0, and raises illegal-instruction otherwise.
   RETIRE_SUCCESS
 }
 
@@ -135,7 +135,7 @@ function clause execute(RMVVTYPE(funct6, vm, vs2, vs1, vd)) = {
   write_single_element(SEW, 0, vd, sum);
   // other elements in vd are treated as tail elements, currently remain unchanged
   // TODO: configuration support for agnostic behavior
-  set_vstart(zeros());
+  // illegal_reduction checks vstart == 0, and raises illegal-instruction otherwise.
   RETIRE_SUCCESS
 }
 

model/extensions/V/vext_vm_insts.sail

@@ -43,7 +43,7 @@ function clause execute(VVMTYPE(funct6, vs2, vs1, vd)) = {
 
   let (initial_result, mask) : (bits('n), bits('n)) = match init_masked_result_carry(num_elem, SEW, LMUL_pow, vd_val) {
     Ok(v)   => v,
-    Err(()) => return Illegal_Instruction()
+    Err(()) => return Illegal_Instruction(),
   };
   var result = initial_result;