Fix potential write to x0 register in RV32A instructions

Fix a potential issue where A extension instructions could
inadvertently write to the x0 register. The fix ensures that such
instructions do not modify the x0 register.

Author: visitorckw

src/rv32_template.c

@@ -1320,7 +1320,8 @@ GEN({
 RVOP(
     lrw,
     {
-        rv->X[ir->rd] = rv->io.mem_read_w(rv->X[ir->rs1]);
+        if (ir->rd)
+            rv->X[ir->rd] = rv->io.mem_read_w(rv->X[ir->rs1]);
         /* skip registration of the 'reservation set'
          * FIXME: uimplemented
          */
@@ -1347,7 +1348,8 @@ RVOP(
 RVOP(
     amoswapw,
     {
-        rv->X[ir->rd] = rv->io.mem_read_w(ir->rs1);
+        if (ir->rd)
+            rv->X[ir->rd] = rv->io.mem_read_w(ir->rs1);
         rv->io.mem_write_s(ir->rs1, rv->X[ir->rs2]);
     },
     GEN({
@@ -1358,7 +1360,8 @@ RVOP(
 RVOP(
     amoaddw,
     {
-        rv->X[ir->rd] = rv->io.mem_read_w(ir->rs1);
+        if (ir->rd)
+            rv->X[ir->rd] = rv->io.mem_read_w(ir->rs1);
         const int32_t res = (int32_t) rv->X[ir->rd] + (int32_t) rv->X[ir->rs2];
         rv->io.mem_write_s(ir->rs1, res);
     },
@@ -1370,7 +1373,8 @@ RVOP(
 RVOP(
     amoxorw,
     {
-        rv->X[ir->rd] = rv->io.mem_read_w(ir->rs1);
+        if (ir->rd)
+            rv->X[ir->rd] = rv->io.mem_read_w(ir->rs1);
         const int32_t res = rv->X[ir->rd] ^ rv->X[ir->rs2];
         rv->io.mem_write_s(ir->rs1, res);
     },
@@ -1382,7 +1386,8 @@ RVOP(
 RVOP(
     amoandw,
     {
-        rv->X[ir->rd] = rv->io.mem_read_w(ir->rs1);
+        if (ir->rd)
+            rv->X[ir->rd] = rv->io.mem_read_w(ir->rs1);
         const int32_t res = rv->X[ir->rd] & rv->X[ir->rs2];
         rv->io.mem_write_s(ir->rs1, res);
     },
@@ -1394,7 +1399,8 @@ RVOP(
 RVOP(
     amoorw,
     {
-        rv->X[ir->rd] = rv->io.mem_read_w(ir->rs1);
+        if (ir->rd)
+            rv->X[ir->rd] = rv->io.mem_read_w(ir->rs1);
         const int32_t res = rv->X[ir->rd] | rv->X[ir->rs2];
         rv->io.mem_write_s(ir->rs1, res);
     },
@@ -1406,7 +1412,8 @@ RVOP(
 RVOP(
     amominw,
     {
-        rv->X[ir->rd] = rv->io.mem_read_w(ir->rs1);
+        if (ir->rd)
+            rv->X[ir->rd] = rv->io.mem_read_w(ir->rs1);
         const int32_t a = rv->X[ir->rd];
         const int32_t b = rv->X[ir->rs2];
         const uint32_t res = a < b ? rv->X[ir->rd] : rv->X[ir->rs2];
@@ -1420,7 +1427,8 @@ RVOP(
 RVOP(
     amomaxw,
     {
-        rv->X[ir->rd] = rv->io.mem_read_w(ir->rs1);
+        if (ir->rd)
+            rv->X[ir->rd] = rv->io.mem_read_w(ir->rs1);
         const int32_t a = rv->X[ir->rd];
         const int32_t b = rv->X[ir->rs2];
         const uint32_t res = a > b ? rv->X[ir->rd] : rv->X[ir->rs2];
@@ -1434,7 +1442,8 @@ RVOP(
 RVOP(
     amominuw,
     {
-        rv->X[ir->rd] = rv->io.mem_read_w(ir->rs1);
+        if (ir->rd)
+            rv->X[ir->rd] = rv->io.mem_read_w(ir->rs1);
         const uint32_t ures =
             rv->X[ir->rd] < rv->X[ir->rs2] ? rv->X[ir->rd] : rv->X[ir->rs2];
         rv->io.mem_write_s(ir->rs1, ures);
@@ -1447,7 +1456,8 @@ RVOP(
 RVOP(
     amomaxuw,
     {
-        rv->X[ir->rd] = rv->io.mem_read_w(ir->rs1);
+        if (ir->rd)
+            rv->X[ir->rd] = rv->io.mem_read_w(ir->rs1);
         const uint32_t ures =
             rv->X[ir->rd] > rv->X[ir->rs2] ? rv->X[ir->rd] : rv->X[ir->rs2];
         rv->io.mem_write_s(ir->rs1, ures);