Re: [PATCH] op_helper: fix some compile warnings

[Yoshinori Sato]

On Mon, 20 Apr 2020 14:49:59 +0900,
Pan Nengyuan wrote:
> 
> We got the following compile-time warnings(gcc7.3):
> /mnt/sdb//qemu/target/rx/op_helper.c: In function ‘helper_scmpu’:
> /mnt/sdb/qemu/target/rx/op_helper.c:213:24: error: ‘tmp1’ may be used 
> uninitialized in this function [-Werror=maybe-uninitialized]
>      env->psw_c = (tmp0 >= tmp1);
>                   ~~~~~~^~~~~~~~
> /mnt/sdb/qemu/target/rx/op_helper.c:213:24: error: ‘tmp0’ may be used 
> uninitialized in this function [-Werror=maybe-uninitialized]
> /mnt/sdb/qemu/target/rx/op_helper.c: In function ‘helper_suntil’:
> /mnt/sdb/qemu/target/rx/op_helper.c:299:23: error: ‘tmp’ may be used 
> uninitialized in this function [-Werror=maybe-uninitialized]
>      env->psw_c = (tmp <= env->regs[2]);
>                   ~~~~~^~~~~~~~~~~~~~~~
> /mnt/sdb/qemu/target/rx/op_helper.c: In function ‘helper_swhile’:
> /mnt/sdb/qemu/target/rx/op_helper.c:318:23: error: ‘tmp’ may be used 
> uninitialized in this function [-Werror=maybe-uninitialized]
>      env->psw_c = (tmp <= env->regs[2]);
> 
> Actually, it looks like a false-positive because it will enter the body of 
> while loop and init it for the first time.
> Let's change 'while' to 'do .. while' to avoid it.

OK.

> Reported-by: Euler Robot <address@hidden>
> Signed-off-by: Pan Nengyuan <address@hidden>
> ---
>  target/rx/op_helper.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/target/rx/op_helper.c b/target/rx/op_helper.c
> index f89d294f2b..b612ab1da8 100644
> --- a/target/rx/op_helper.c
> +++ b/target/rx/op_helper.c
> @@ -201,14 +201,14 @@ void helper_scmpu(CPURXState *env)
>      if (env->regs[3] == 0) {
>          return;
>      }
> -    while (env->regs[3] != 0) {
> +    do {
>          tmp0 = cpu_ldub_data_ra(env, env->regs[1]++, GETPC());
>          tmp1 = cpu_ldub_data_ra(env, env->regs[2]++, GETPC());
>          env->regs[3]--;
>          if (tmp0 != tmp1 || tmp0 == '\0') {
>              break;
>          }
> -    }
> +    } while (env->regs[3] != 0);
>      env->psw_z = tmp0 - tmp1;
>      env->psw_c = (tmp0 >= tmp1);
>  }
> @@ -287,14 +287,14 @@ void helper_suntil(CPURXState *env, uint32_t sz)
>      if (env->regs[3] == 0) {
>          return ;
>      }
> -    while (env->regs[3] != 0) {
> +    do {
>          tmp = cpu_ldufn[sz](env, env->regs[1], GETPC());
>          env->regs[1] += 1 << sz;
>          env->regs[3]--;
>          if (tmp == env->regs[2]) {
>              break;
>          }
> -    }
> +    } while (env->regs[3] != 0);
>      env->psw_z = tmp - env->regs[2];
>      env->psw_c = (tmp <= env->regs[2]);
>  }
> @@ -306,14 +306,14 @@ void helper_swhile(CPURXState *env, uint32_t sz)
>      if (env->regs[3] == 0) {
>          return ;
>      }
> -    while (env->regs[3] != 0) {
> +    do {
>          tmp = cpu_ldufn[sz](env, env->regs[1], GETPC());
>          env->regs[1] += 1 << sz;
>          env->regs[3]--;
>          if (tmp != env->regs[2]) {
>              break;
>          }
> -    }
> +    } while (env->regs[3] != 0);
>      env->psw_z = env->regs[3];
>      env->psw_c = (tmp <= env->regs[2]);
>  }
> -- 
> 2.18.2
> 
> 

It looks different result in env->regs[3] is zero.
In such a case, nothing changes.

I think that the warning of the uninitialized variable
will disappear by fixing as follows.

From 5de0c54a970e01e96b41870252d0ea54ec61c540 Mon Sep 17 00:00:00 2001
From: Yoshinori Sato <address@hidden>
Date: Mon, 20 Apr 2020 17:41:04 +0900
Subject: [PATCH] target/rx/op_helper: Fix uninitialized warning.

Signed-off-by: Yoshinori Sato <address@hidden>
---
 target/rx/op_helper.c | 101 ++++++++++++++++++++----------------------
 1 file changed, 49 insertions(+), 52 deletions(-)

diff --git a/target/rx/op_helper.c b/target/rx/op_helper.c
index f89d294f2b..f84f6c706c 100644
--- a/target/rx/op_helper.c
+++ b/target/rx/op_helper.c
@@ -284,38 +284,36 @@ void helper_suntil(CPURXState *env, uint32_t sz)
 {
     uint32_t tmp;
     tcg_debug_assert(sz < 3);
-    if (env->regs[3] == 0) {
-        return ;
-    }
-    while (env->regs[3] != 0) {
-        tmp = cpu_ldufn[sz](env, env->regs[1], GETPC());
-        env->regs[1] += 1 << sz;
-        env->regs[3]--;
-        if (tmp == env->regs[2]) {
-            break;
+    if (env->regs[3] > 0) {
+        while (env->regs[3] != 0) {
+            tmp = cpu_ldufn[sz](env, env->regs[1], GETPC());
+            env->regs[1] += 1 << sz;
+            env->regs[3]--;
+            if (tmp == env->regs[2]) {
+                break;
+            }
         }
+        env->psw_z = tmp - env->regs[2];
+        env->psw_c = (tmp <= env->regs[2]);
     }
-    env->psw_z = tmp - env->regs[2];
-    env->psw_c = (tmp <= env->regs[2]);
 }
 
 void helper_swhile(CPURXState *env, uint32_t sz)
 {
     uint32_t tmp;
     tcg_debug_assert(sz < 3);
-    if (env->regs[3] == 0) {
-        return ;
-    }
-    while (env->regs[3] != 0) {
-        tmp = cpu_ldufn[sz](env, env->regs[1], GETPC());
-        env->regs[1] += 1 << sz;
-        env->regs[3]--;
-        if (tmp != env->regs[2]) {
-            break;
+    if (env->regs[3] > 0) {
+        while (env->regs[3] != 0) {
+            tmp = cpu_ldufn[sz](env, env->regs[1], GETPC());
+            env->regs[1] += 1 << sz;
+            env->regs[3]--;
+            if (tmp != env->regs[2]) {
+                break;
+            }
         }
+        env->psw_z = env->regs[3];
+        env->psw_c = (tmp <= env->regs[2]);
     }
-    env->psw_z = env->regs[3];
-    env->psw_c = (tmp <= env->regs[2]);
 }
 
 /* accumlator operations */
@@ -325,40 +323,39 @@ void helper_rmpa(CPURXState *env, uint32_t sz)
     int32_t result_h;
     int64_t tmp0, tmp1;
 
-    if (env->regs[3] == 0) {
-        return;
-    }
-    result_l = env->regs[5];
-    result_l <<= 32;
-    result_l |= env->regs[4];
-    result_h = env->regs[6];
-    env->psw_o = 0;
+    if (env->regs[3] > 0) {
+        result_l = env->regs[5];
+        result_l <<= 32;
+        result_l |= env->regs[4];
+        result_h = env->regs[6];
+        env->psw_o = 0;
 
-    while (env->regs[3] != 0) {
-        tmp0 = cpu_ldfn[sz](env, env->regs[1], GETPC());
-        tmp1 = cpu_ldfn[sz](env, env->regs[2], GETPC());
-        tmp0 *= tmp1;
-        prev = result_l;
-        result_l += tmp0;
-        /* carry / bollow */
-        if (tmp0 < 0) {
-            if (prev > result_l) {
-                result_h--;
-            }
-        } else {
-            if (prev < result_l) {
-                result_h++;
+        while (env->regs[3] != 0) {
+            tmp0 = cpu_ldfn[sz](env, env->regs[1], GETPC());
+            tmp1 = cpu_ldfn[sz](env, env->regs[2], GETPC());
+            tmp0 *= tmp1;
+            prev = result_l;
+            result_l += tmp0;
+            /* carry / bollow */
+            if (tmp0 < 0) {
+                if (prev > result_l) {
+                    result_h--;
+                }
+            } else {
+                if (prev < result_l) {
+                    result_h++;
+                }
             }
-        }
 
-        env->regs[1] += 1 << sz;
-        env->regs[2] += 1 << sz;
+            env->regs[1] += 1 << sz;
+            env->regs[2] += 1 << sz;
+        }
+        env->psw_s = result_h;
+        env->psw_o = (result_h != 0 && result_h != -1) << 31;
+        env->regs[6] = result_h;
+        env->regs[5] = result_l >> 32;
+        env->regs[4] = result_l & 0xffffffff;
     }
-    env->psw_s = result_h;
-    env->psw_o = (result_h != 0 && result_h != -1) << 31;
-    env->regs[6] = result_h;
-    env->regs[5] = result_l >> 32;
-    env->regs[4] = result_l & 0xffffffff;
 }
 
 void helper_racw(CPURXState *env, uint32_t imm)
-- 
2.20.1

-- 
Yosinori Sato