[C++ PATCH] Diagnose constexpr overflow (PR c++/70323)

[C++ PATCH] Diagnose constexpr overflow (PR c++/70323)

[Jakub Jelinek]

Hi!

On the following testcase, the first function is cp_folded into
return i == 0 ? 2147483648(OVF): 2147483647;
The problem is that we don't diagnose then the overflow at all.
We already have code that sets *overflow_p under right conditions,
just there wasn't any permerror call.

Fixed thusly, bootstrapped/regtested on x86_64-linux and i686-linux, ok for
trunk?

2016-03-22  Jakub Jelinek  <jakub@redhat.com>

	PR c++/70323
	* constexpr.c (cxx_eval_constant_expression): Diagnose overflow
	on TREE_OVERFLOW constants.

	* g++.dg/cpp0x/constexpr-70323.C: New test.

--- gcc/cp/constexpr.c.jj	2016-03-22 09:05:32.000000000 +0100
+++ gcc/cp/constexpr.c	2016-03-22 10:38:58.598077573 +0100
@@ -3306,8 +3306,13 @@ cxx_eval_constant_expression (const cons
     }
   if (CONSTANT_CLASS_P (t))
     {
-      if (TREE_OVERFLOW (t) && (!flag_permissive || ctx->quiet))
-	*overflow_p = true;
+      if (TREE_OVERFLOW (t))
+	{
+	  if (!ctx->quiet)
+	    permerror (input_location, "overflow in constant expression");
+	  if (!flag_permissive || ctx->quiet)
+	    *overflow_p = true;
+	}
       return t;
     }
 
--- gcc/testsuite/g++.dg/cpp0x/constexpr-70323.C.jj	2016-03-22 10:42:54.093884158 +0100
+++ gcc/testsuite/g++.dg/cpp0x/constexpr-70323.C	2016-03-22 10:42:29.000000000 +0100
@@ -0,0 +1,10 @@
+// PR c++/70323
+// { dg-do compile { target c++11 } }
+
+constexpr int overflow_if_0 (int i) { return __INT_MAX__ + !i; }
+constexpr int overflow_if_1 (int i) { return __INT_MAX__ + i; }
+
+constexpr bool i0_0 = overflow_if_0 (0);   // { dg-error "overflow in constant expression" }
+constexpr bool i0_1 = overflow_if_0 (1);
+constexpr bool i1_0 = overflow_if_1 (0);
+constexpr bool i1_1 = overflow_if_1 (1);   // { dg-error "overflow in constant expression" }

	Jakub

Re: [C++ PATCH] Diagnose constexpr overflow (PR c++/70323)

[Jason Merrill]

For GCC 7 we should do constexpr evaluation on the unfolded function, 
but for GCC 6 this is OK.

Jason

Re: [C++ PATCH] Diagnose constexpr overflow (PR c++/70323)

[Jason Merrill]

[-- Attachment #1: Type: text/plain, Size: 233 bytes --]

On 03/23/2016 02:34 PM, Jason Merrill wrote:
> For GCC 7 we should do constexpr evaluation on the unfolded function,
> but for GCC 6 this is OK.

And here's a fix for the -Wall case.

Tested x86_64-pc-linux-gnu, applying to trunk.



[-- Attachment #2: 70323.patch --]
[-- Type: text/x-patch, Size: 1386 bytes --]

commit 75f153ad9c455c7f2340b6da6791e5a9a0787a8e
Author: Jason Merrill <jason@redhat.com>
Date:   Thu Mar 24 12:53:32 2016 -0400

    	PR c++/70323
    	* constexpr.c (cxx_eval_call_expression): Don't cache result if
    	*overflow_p.

diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index 8427513..2d30a84 100644
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -1448,7 +1448,7 @@ cxx_eval_call_expression (const constexpr_ctx *ctx, tree t,
 
       if (result == error_mark_node)
 	*non_constant_p = true;
-      if (*non_constant_p)
+      if (*non_constant_p || *overflow_p)
 	result = error_mark_node;
       else if (!result)
 	result = void_node;
diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-70323a.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-70323a.C
new file mode 100644
index 0000000..d166787
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-70323a.C
@@ -0,0 +1,11 @@
+// PR c++/70323
+// { dg-do compile { target c++11 } }
+// { dg-options "-Wall" }
+
+constexpr int overflow_if_0 (int i) { return __INT_MAX__ + !i; }
+constexpr int overflow_if_1 (int i) { return __INT_MAX__ + i; }
+
+constexpr bool i0_0 = overflow_if_0 (0);   // { dg-error "overflow in constant expression" }
+constexpr bool i0_1 = overflow_if_0 (1);
+constexpr bool i1_0 = overflow_if_1 (0);
+constexpr bool i1_1 = overflow_if_1 (1);   // { dg-error "overflow in constant expression" }