[PATCH] RISC-V: Fix incorrect code of touching inaccessible memory address

[juzhe . zhong]

From: Juzhe-Zhong <juzhe.zh...@rivai.ai>

For VLMAX situation, rtx len = ops[m_op_num] is incorrect since
the last element the ops array should be ops[m_op_num - 1];

I notice this issue when I am debugging code.
This is a code bug even though the following codes will hide this issue.
We still should need this minor fix.

Built && Regression PASSed.

Ok for trunk?
  
gcc/ChangeLog:

        * config/riscv/riscv-v.cc: Fix bug of touching inaccessible memory.

---
 gcc/config/riscv/riscv-v.cc | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/gcc/config/riscv/riscv-v.cc b/gcc/config/riscv/riscv-v.cc
index fa61a850a22..a0992773644 100644
--- a/gcc/config/riscv/riscv-v.cc
+++ b/gcc/config/riscv/riscv-v.cc
@@ -169,7 +169,11 @@ public:
 
     if (m_needs_avl_p)
       {
-       rtx len = ops[m_op_num];
+       /* The variable "m_op_num" means the real operation operands except VL
+          operand. For VLMAX patterns (no VL operand), the last operand is
+          ops[m_op_num -1]. Wheras for non-VLMAX patterns, the last operand is
+          VL operand which is ops[m_op_num].  */
+       rtx len = NULL_RTX;
        if (m_vlmax_p)
          {
            if (const_vlmax_p (m_dest_mode))
@@ -185,6 +189,20 @@ public:
                len = gen_reg_rtx (Pmode);
                emit_vlmax_vsetvl (m_dest_mode, len);
              }
+           else
+             {
+               /* According to LRA mov pattern in vector.md. The VL operand is
+                  always the last operand.  */
+               gcc_assert (ops[m_op_num]);
+               len = ops[m_op_num];
+             }
+         }
+       else
+         {
+           /* For non-VLMAX patterns. The VL operand is always the last
+            * operand.  */
+           gcc_assert (ops[m_op_num]);
+           len = ops[m_op_num];
          }
        add_input_operand (len, Pmode);
       }
-- 
2.36.3