[PATCH] Fix PR c++/66590: incorrect warning "reaches end of non-void function" for switch

[PATCH] Fix PR c++/66590: incorrect warning "reaches end of non-void function" for switch

[apinski]

From: Andrew Pinski <apinski@marvell.com>

So the problem here is there is code in the C++ front-end not to add a
break statement (to the IR) if the previous block does not fall through.
The problem is the code which does the check to see if the block
may fallthrough does not check a CLEANUP_STMT; it assumes it is always
fall through.  Anyways this adds the code for the case of a CLEANUP_STMT
that is only for !CLEANUP_EH_ONLY (the try/finally case).

OK? Bootstrapped and tested on x86_64-linux-gnu with no regressions.

gcc/cp/ChangeLog:

	* cp-objcp-common.c (cxx_block_may_fallthru): Handle
	CLEANUP_STMT for the case which will be try/finally.

gcc/testsuite/ChangeLog:

	* g++.dg/warn/Wreturn-5.C: New test.
---
 gcc/cp/cp-objcp-common.c              |  9 +++++++++
 gcc/testsuite/g++.dg/warn/Wreturn-5.C | 15 +++++++++++++++
 2 files changed, 24 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/warn/Wreturn-5.C

diff --git a/gcc/cp/cp-objcp-common.c b/gcc/cp/cp-objcp-common.c
index beef0123b04..43888507b85 100644
--- a/gcc/cp/cp-objcp-common.c
+++ b/gcc/cp/cp-objcp-common.c
@@ -317,6 +317,15 @@ cxx_block_may_fallthru (const_tree stmt)
 	return true;
       return block_may_fallthru (ELSE_CLAUSE (stmt));
 
+    case CLEANUP_STMT:
+      /* Just handle the try/finally cases.  */
+      if (!CLEANUP_EH_ONLY (stmt))
+	{
+	  return (block_may_fallthru (CLEANUP_BODY (stmt))
+		  && block_may_fallthru (CLEANUP_EXPR (stmt)));
+	}
+      return true;
+
     default:
       return c_block_may_fallthru (stmt);
     }
diff --git a/gcc/testsuite/g++.dg/warn/Wreturn-5.C b/gcc/testsuite/g++.dg/warn/Wreturn-5.C
new file mode 100644
index 00000000000..543e33e905d
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wreturn-5.C
@@ -0,0 +1,15 @@
+// PR C++/66590
+// { dg-do compile }
+// { dg-options "-Wall" }
+
+struct A{ ~A();};
+
+int f(int x)
+{
+    A a;
+    switch (x)
+    {
+        case 1: { A tmp; return 1; } break;
+        default: return 0;
+    }
+}	// { dg-bogus "control reaches end of non-void function" }
-- 
2.27.0

Re: [PATCH] Fix PR c++/66590: incorrect warning "reaches end of non-void function" for switch

[Jason Merrill]

On 8/13/21 2:40 PM, apinski--- via Gcc-patches wrote:
> From: Andrew Pinski <apinski@marvell.com>
> 
> So the problem here is there is code in the C++ front-end not to add a
> break statement (to the IR) if the previous block does not fall through.
> The problem is the code which does the check to see if the block
> may fallthrough does not check a CLEANUP_STMT; it assumes it is always
> fall through.  Anyways this adds the code for the case of a CLEANUP_STMT
> that is only for !CLEANUP_EH_ONLY (the try/finally case).
> 
> OK? Bootstrapped and tested on x86_64-linux-gnu with no regressions.

OK, thanks.

> gcc/cp/ChangeLog:
> 
> 	* cp-objcp-common.c (cxx_block_may_fallthru): Handle
> 	CLEANUP_STMT for the case which will be try/finally.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/warn/Wreturn-5.C: New test.
> ---
>   gcc/cp/cp-objcp-common.c              |  9 +++++++++
>   gcc/testsuite/g++.dg/warn/Wreturn-5.C | 15 +++++++++++++++
>   2 files changed, 24 insertions(+)
>   create mode 100644 gcc/testsuite/g++.dg/warn/Wreturn-5.C
> 
> diff --git a/gcc/cp/cp-objcp-common.c b/gcc/cp/cp-objcp-common.c
> index beef0123b04..43888507b85 100644
> --- a/gcc/cp/cp-objcp-common.c
> +++ b/gcc/cp/cp-objcp-common.c
> @@ -317,6 +317,15 @@ cxx_block_may_fallthru (const_tree stmt)
>   	return true;
>         return block_may_fallthru (ELSE_CLAUSE (stmt));
>   
> +    case CLEANUP_STMT:
> +      /* Just handle the try/finally cases.  */
> +      if (!CLEANUP_EH_ONLY (stmt))
> +	{
> +	  return (block_may_fallthru (CLEANUP_BODY (stmt))
> +		  && block_may_fallthru (CLEANUP_EXPR (stmt)));
> +	}
> +      return true;
> +
>       default:
>         return c_block_may_fallthru (stmt);
>       }
> diff --git a/gcc/testsuite/g++.dg/warn/Wreturn-5.C b/gcc/testsuite/g++.dg/warn/Wreturn-5.C
> new file mode 100644
> index 00000000000..543e33e905d
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/warn/Wreturn-5.C
> @@ -0,0 +1,15 @@
> +// PR C++/66590
> +// { dg-do compile }
> +// { dg-options "-Wall" }
> +
> +struct A{ ~A();};
> +
> +int f(int x)
> +{
> +    A a;
> +    switch (x)
> +    {
> +        case 1: { A tmp; return 1; } break;
> +        default: return 0;
> +    }
> +}	// { dg-bogus "control reaches end of non-void function" }
>