Fix Arm outputs for right shift operations

Let shecc generate arithmetic shift right instructions for
right shift operations instead of using logical shift right
instructions.

Currently, the behavior of right shift operations is consistent
with GCC and Clang.

Author: DrXiao

src/arm-codegen.c

@@ -408,7 +408,7 @@ void emit_ph2_ir(ph2_ir_t *ph2_ir)
         emit(__sll(__AL, rd, rn, rm));
         return;
     case OP_rshift:
-        emit(__srl(__AL, rd, rn, rm));
+        emit(__sra(__AL, rd, rn, rm));
         return;
     case OP_eq:
     case OP_neq:

src/arm.c

@@ -226,6 +226,12 @@ int __sll_amt(arm_cond_t cond,
                       rm + (0 << 4) + (shift << 5) + (amt << 7));
 }
 
+int __sra(arm_cond_t cond, arm_reg rd, arm_reg rm, arm_reg rs)
+{
+    return arm_encode(cond, 0 + (arm_mov << 1) + (0 << 5), 0, rd,
+                      rm + (5 << 4) + (rs << 8));
+}
+
 int __add_i(arm_cond_t cond, arm_reg rd, arm_reg rs, int imm)
 {
     if (imm >= 0)

tests/driver.sh

@@ -120,6 +120,12 @@ expr 1 "1 && 1"
 
 expr 16 "2 << 3"
 expr 32 "256 >> 3"
+try_output 0 "128 59926 -6 -4 -500283"  << EOF
+int main() {
+  printf("%d %d %d %d %d", 32768 >> 8, 245458999 >> 12, -11 >> 1, -16 >> 2, -1000565 >> 1);
+  return 0;
+}
+EOF
 expr 239 "237 | 106"
 expr 135 "237 ^ 106"
 expr 104 "237 & 106"