[PATCH][C++] Fix PR67333

[PATCH][C++] Fix PR67333

[Mikhail Maltsev]

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Hi.
This patch fixes a rejects-valid bug related to volatile-qualified arguments of
constexpr functions. This is essentially a one-line change in constexpr.c.
Bootstrapped and regtested on x86_64-pc-linux-gnu. OK for trunk?

gcc/cp/ChangeLog:

2015-08-25  Mikhail Maltsev  <maltsevm@gmail.com>

        PR c++/67333
        * constexpr.c (potential_constant_expression_1): Do not reject
        volatile-qualified values, if there is no lvalue-to-rvalue conversion.

gcc/testsuite/ChangeLog:

2015-08-25  Mikhail Maltsev  <maltsevm@gmail.com>

        PR c++/67333
        * g++.dg/cpp0x/constexpr-67333.C: New test.
        * g++.dg/cpp1y/constexpr-67333.C: New test.

-- 
Regards,
    Mikhail Maltsev

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diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index 1eacb8b..f4ee727 100644
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -4006,7 +4006,7 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict,
     return false;
   if (t == NULL_TREE)
     return true;
-  if (TREE_THIS_VOLATILE (t))
+  if (TREE_THIS_VOLATILE (t) && (!DECL_P (t) || want_rval))
     {
       if (flags & tf_error)
         error ("expression %qE has side-effects", t);
diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-67333.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-67333.C
new file mode 100644
index 0000000..885ece6
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-67333.C
@@ -0,0 +1,29 @@
+// PR c++/67333
+// { dg-do compile { target c++11 } }
+
+template <int N>
+struct integral_constant
+{
+  static constexpr int value = N;
+};
+
+template <typename T, int S>
+constexpr int lengthof (const volatile T (&)[S])
+{
+  return S;
+}
+
+template <typename T, int S>
+constexpr int valueof (const volatile T (&s)[S])  // { dg-error "has side-effects" }
+{
+  return s[0];
+}
+
+int main ()
+{
+  volatile int meow[4] {};
+  integral_constant<lengthof (meow)>::value;  // OK
+  integral_constant<valueof (meow)>::value;   // { dg-error "in a constant expression" }
+  return 0;
+}
+
diff --git a/gcc/testsuite/g++.dg/cpp1y/constexpr-67333.C b/gcc/testsuite/g++.dg/cpp1y/constexpr-67333.C
new file mode 100644
index 0000000..7e3ef21
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/constexpr-67333.C
@@ -0,0 +1,26 @@
+// PR c++/67333
+// { dg-do compile { target c++14 } }
+
+template <int N>
+struct integral_constant
+{
+  static constexpr int value = N;
+};
+
+constexpr int decl (int x)
+{
+  volatile int v = x;
+  return x;
+}
+
+constexpr int use (int x)
+{
+  volatile int v = x;
+  return v;
+} // { dg-error "has side-effects" }
+
+int main()
+{
+  integral_constant<decl (2)>::value; // OK
+  integral_constant<use (2)>::value;  // { dg-error "in a constant expression" }
+}

[PATCH][PING][C++] Fix PR67333

[Mikhail Maltsev]

Ping.

On 08/27/2015 09:27 PM, Mikhail Maltsev wrote:
> Hi.
> This patch fixes a rejects-valid bug related to volatile-qualified arguments of
> constexpr functions. This is essentially a one-line change in constexpr.c.
> Bootstrapped and regtested on x86_64-pc-linux-gnu. OK for trunk?
> 
> gcc/cp/ChangeLog:
> 
> 2015-08-25  Mikhail Maltsev  <maltsevm@gmail.com>
> 
>         PR c++/67333
>         * constexpr.c (potential_constant_expression_1): Do not reject
>         volatile-qualified values, if there is no lvalue-to-rvalue conversion.
> 
> gcc/testsuite/ChangeLog:
> 
> 2015-08-25  Mikhail Maltsev  <maltsevm@gmail.com>
> 
>         PR c++/67333
>         * g++.dg/cpp0x/constexpr-67333.C: New test.
>         * g++.dg/cpp1y/constexpr-67333.C: New test.
> 

-- 
Regards,
    Mikhail Maltsev

[PATCH][PING^2][C++] Fix PR67333

[Mikhail Maltsev]

PING.

On 08/27/2015 09:27 PM, Mikhail Maltsev wrote:
> Hi.
> This patch fixes a rejects-valid bug related to volatile-qualified arguments of
> constexpr functions. This is essentially a one-line change in constexpr.c.
> Bootstrapped and regtested on x86_64-pc-linux-gnu. OK for trunk?
> 
> gcc/cp/ChangeLog:
> 
> 2015-08-25  Mikhail Maltsev  <maltsevm@gmail.com>
> 
>         PR c++/67333
>         * constexpr.c (potential_constant_expression_1): Do not reject
>         volatile-qualified values, if there is no lvalue-to-rvalue conversion.
> 
> gcc/testsuite/ChangeLog:
> 
> 2015-08-25  Mikhail Maltsev  <maltsevm@gmail.com>
> 
>         PR c++/67333
>         * g++.dg/cpp0x/constexpr-67333.C: New test.
>         * g++.dg/cpp1y/constexpr-67333.C: New test.
> 

-- 
Regards,
    Mikhail Maltsev

Re: [PATCH][C++] Fix PR67333

[Jason Merrill]

Hi, sorry for the slow response.  Please feel free to ping once a week.

On 08/27/2015 02:27 PM, Mikhail Maltsev wrote:
> +  if (TREE_THIS_VOLATILE (t) && (!DECL_P (t) || want_rval))

Why the !DECL_P check?  Pulling the value out of a volatile INDIRECT_REF 
is just as problematic as from a variable.

Jason

Re: [PATCH][C++] Fix PR67333

[Mikhail Maltsev]

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On 10/06/2015 04:46 PM, Jason Merrill wrote:
> Hi, sorry for the slow response.  Please feel free to ping once a week.
> 
> On 08/27/2015 02:27 PM, Mikhail Maltsev wrote:
>> +  if (TREE_THIS_VOLATILE (t) && (!DECL_P (t) || want_rval))
> 
> Why the !DECL_P check?  Pulling the value out of a volatile INDIRECT_REF is just
> as problematic as from a variable.
Hmm... my intent was to check that we are not dealing with an expression, i.e.
that should have been 'EXPR_P' rather than '!DECL_P'.

I changed the condition to 'TREE_THIS_VOLATILE (t) && (EXPR_P (t) || want_rval)'
and also added one more test (the one with 'test_ref' function). The updated
patch passes bootstrap & regtest on x86_64-pc-linux-gnu.

But now I wonder, if the combination 'TREE_THIS_VOLATILE (t) && EXPR_P (t) &&
!want_rval' is possible at all and should it be rejected?

-- 
Regards,
    Mikhail Maltsev

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diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index ec9710c..b23d52a 100644
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -4006,7 +4006,7 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict,
     return false;
   if (t == NULL_TREE)
     return true;
-  if (TREE_THIS_VOLATILE (t))
+  if (TREE_THIS_VOLATILE (t) && (EXPR_P (t) || want_rval))
     {
       if (flags & tf_error)
         error ("expression %qE has side-effects", t);
diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-67333.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-67333.C
new file mode 100644
index 0000000..885ece6
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-67333.C
@@ -0,0 +1,29 @@
+// PR c++/67333
+// { dg-do compile { target c++11 } }
+
+template <int N>
+struct integral_constant
+{
+  static constexpr int value = N;
+};
+
+template <typename T, int S>
+constexpr int lengthof (const volatile T (&)[S])
+{
+  return S;
+}
+
+template <typename T, int S>
+constexpr int valueof (const volatile T (&s)[S])  // { dg-error "has side-effects" }
+{
+  return s[0];
+}
+
+int main ()
+{
+  volatile int meow[4] {};
+  integral_constant<lengthof (meow)>::value;  // OK
+  integral_constant<valueof (meow)>::value;   // { dg-error "in a constant expression" }
+  return 0;
+}
+
diff --git a/gcc/testsuite/g++.dg/cpp1y/constexpr-67333.C b/gcc/testsuite/g++.dg/cpp1y/constexpr-67333.C
new file mode 100644
index 0000000..333047a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/constexpr-67333.C
@@ -0,0 +1,36 @@
+// PR c++/67333
+// { dg-do compile { target c++14 } }
+
+template <int N>
+struct integral_constant
+{
+  static constexpr int value = N;
+};
+
+constexpr int decl (int x)
+{
+  volatile int v = x;
+  return x;
+}
+
+constexpr int use (int x)
+{
+  volatile int v = x;
+  return v;
+} // { dg-error "has side-effects" }
+
+constexpr int test_ref (volatile int &x)
+{
+  volatile int &vol_ref = x;
+  volatile int *vol_ptr = &x;
+  volatile int &vol_deref = *vol_ptr;
+  return 0;
+}
+
+int main()
+{
+  volatile int x = 0;
+  constexpr int t = test_ref (x);
+  integral_constant<decl (2)>::value; // OK
+  integral_constant<use (2)>::value;  // { dg-error "in a constant expression" }
+}

Re: [PATCH][C++] Fix PR67333

[Jason Merrill]

On 10/17/2015 08:57 AM, Mikhail Maltsev wrote:
> On 10/06/2015 04:46 PM, Jason Merrill wrote:
>> Hi, sorry for the slow response.  Please feel free to ping once a week.
>>
>> On 08/27/2015 02:27 PM, Mikhail Maltsev wrote:
>>> +  if (TREE_THIS_VOLATILE (t) && (!DECL_P (t) || want_rval))
>>
>> Why the !DECL_P check?  Pulling the value out of a volatile INDIRECT_REF is just
>> as problematic as from a variable.

> Hmm... my intent was to check that we are not dealing with an expression, i.e.
> that should have been 'EXPR_P' rather than '!DECL_P'.

But why do you want to check that?  My point is that the same issue can 
occur with an expression.  Can't you just check want_rval?

> But now I wonder, if the combination 'TREE_THIS_VOLATILE (t) && EXPR_P (t) &&
> !want_rval' is possible at all and should it be rejected?

It is possible for a volatile *_REF.

Jason