c++: Reject some further reinterpret casts in constexpr [PR82304, PR95307]

cxx_eval_outermost_constant_expr had a check for reinterpret_casts from
pointers (well, it checked from ADDR_EXPRs) to integral type, but that
only caught such cases at the toplevel of expressions.
As the comment said, it should be done even inside of the expressions,
but at the point of the writing e.g. pointer differences used to be a
problem.  We now have POINTER_DIFF_EXPR, so this is no longer an issue.

Had to do it just for CONVERT_EXPR, because the FE emits NOP_EXPR casts
from pointers to integrals in various spots, e.g. for the PMR & 1 tests,
though on NOP_EXPR we have the REINTERPRET_CAST_P bit that we do check,
while on CONVERT_EXPR we don't.

2020-06-04  Jakub Jelinek  <jakub@redhat.com>

	PR c++/82304
	PR c++/95307
	* constexpr.c (cxx_eval_constant_expression): Diagnose CONVERT_EXPR
	conversions from pointer types to arithmetic types here...
	(cxx_eval_outermost_constant_expr): ... instead of here.

	* g++.dg/template/pr79650.C: Expect different diagnostics and expect
	it on all lines that do pointer to integer casts.
	* g++.dg/cpp1y/constexpr-shift1.C: Expect different diagnostics.
	* g++.dg/cpp1y/constexpr-82304.C: New test.
	* g++.dg/cpp0x/constexpr-95307.C: New test.

diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index 959f0254d09d7f38c4609454b817e66fbd2ae178..c7d17e9b86e0b6055b97e353256ca7e075fe571c 100644 (file)
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -6210,6 +6210,18 @@ cxx_eval_constant_expression (const constexpr_ctx *ctx, tree t,
        if (VOID_TYPE_P (type))
          return void_node;
 
+       if (TREE_CODE (t) == CONVERT_EXPR
+           && ARITHMETIC_TYPE_P (type)
+           && INDIRECT_TYPE_P (TREE_TYPE (op)))
+         {
+           if (!ctx->quiet)
+             error_at (loc,
+                       "conversion from pointer type %qT to arithmetic type "
+                       "%qT in a constant expression", TREE_TYPE (op), type);
+           *non_constant_p = true;
+           return t;
+         }
+
        if (TREE_CODE (op) == PTRMEM_CST && !TYPE_PTRMEM_P (type))
          op = cplus_expand_constant (op);
 
@@ -6811,19 +6823,6 @@ cxx_eval_outermost_constant_expr (tree t, bool allow_non_constant,
       non_constant_p = true;
     }
 
-  /* Technically we should check this for all subexpressions, but that
-     runs into problems with our internal representation of pointer
-     subtraction and the 5.19 rules are still in flux.  */
-  if (CONVERT_EXPR_CODE_P (TREE_CODE (r))
-      && ARITHMETIC_TYPE_P (TREE_TYPE (r))
-      && TREE_CODE (TREE_OPERAND (r, 0)) == ADDR_EXPR)
-    {
-      if (!allow_non_constant)
-       error ("conversion from pointer type %qT "
-              "to arithmetic type %qT in a constant expression",
-              TREE_TYPE (TREE_OPERAND (r, 0)), TREE_TYPE (r));
-      non_constant_p = true;
-    }
 
   if (!non_constant_p && overflow_p)
     non_constant_p = true;

diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-95307.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-95307.C
new file mode 100644 (file)
index 0000000..bd3c6a8
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-95307.C
@@ -0,0 +1,5 @@
+// PR c++/95307
+// { dg-do compile { target c++11 } }
+
+int v;
+constexpr auto p{reinterpret_cast<__UINTPTR_TYPE__>(&v) - 1u}; // { dg-error "conversion from pointer type" }

diff --git a/gcc/testsuite/g++.dg/cpp1y/constexpr-82304.C b/gcc/testsuite/g++.dg/cpp1y/constexpr-82304.C
new file mode 100644 (file)
index 0000000..3b05243
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/constexpr-82304.C
@@ -0,0 +1,14 @@
+// PR c++/82304
+// { dg-do compile { target c++14 } }
+
+typedef __UINTPTR_TYPE__ uintptr_t;
+
+constexpr const char *
+foo (const char *p)
+{
+  auto l = reinterpret_cast<uintptr_t>(p);     // { dg-error "conversion from pointer" }
+  ++l;
+  return reinterpret_cast<const char *>(l);
+}
+
+constexpr auto s = foo ("Hello");

diff --git a/gcc/testsuite/g++.dg/cpp1y/constexpr-shift1.C b/gcc/testsuite/g++.dg/cpp1y/constexpr-shift1.C
index d63c954f42f7c3ce2115a8677dcdda909bd1eb00..e0e56e262f0ca654b2d87d0d7322dd84cfc145c8 100644 (file)
--- a/gcc/testsuite/g++.dg/cpp1y/constexpr-shift1.C
+++ b/gcc/testsuite/g++.dg/cpp1y/constexpr-shift1.C
@@ -3,7 +3,7 @@
 constexpr int p = 1;
 constexpr __PTRDIFF_TYPE__ bar (int a)
 {
-  return ((__PTRDIFF_TYPE__) &p) << a; // { dg-error "is not a constant expression" }
+  return ((__PTRDIFF_TYPE__) &p) << a; // { dg-error "conversion from pointer" }
 }
 constexpr __PTRDIFF_TYPE__ r = bar (2); // { dg-message "in .constexpr. expansion of" }
-constexpr __PTRDIFF_TYPE__ s = bar (0); // { dg-error "conversion from pointer" }
+constexpr __PTRDIFF_TYPE__ s = bar (0);

diff --git a/gcc/testsuite/g++.dg/template/pr79650.C b/gcc/testsuite/g++.dg/template/pr79650.C
index 72c781409426cb036990ff71a2ef8191d36e839d..11d28c5b2077ef241053c818540878f247266f75 100644 (file)
--- a/gcc/testsuite/g++.dg/template/pr79650.C
+++ b/gcc/testsuite/g++.dg/template/pr79650.C
@@ -11,10 +11,10 @@ foo ()
   static int a, b;
 lab1:
 lab2:
-  A<(intptr_t)&&lab1 - (__INTPTR_TYPE__)&&lab2> c;     // { dg-error "not a constant integer" }
-  A<(intptr_t)&&lab1 - (__INTPTR_TYPE__)&&lab1> d;
-  A<(intptr_t)&a - (intptr_t)&b> e;                    // { dg-error "is not a constant expression" }
-  A<(intptr_t)&a - (intptr_t)&a> f;
-  A<(intptr_t)sizeof(a) + (intptr_t)&a> g;             // { dg-error "not a constant integer" }
+  A<(intptr_t)&&lab1 - (__INTPTR_TYPE__)&&lab2> c;     // { dg-error "conversion from pointer type" }
+  A<(intptr_t)&&lab1 - (__INTPTR_TYPE__)&&lab1> d;     // { dg-error "conversion from pointer type" }
+  A<(intptr_t)&a - (intptr_t)&b> e;                    // { dg-error "conversion from pointer type" }
+  A<(intptr_t)&a - (intptr_t)&a> f;                    // { dg-error "conversion from pointer type" }
+  A<(intptr_t)sizeof(a) + (intptr_t)&a> g;             // { dg-error "conversion from pointer type" }
   A<(intptr_t)&a> h;                                   // { dg-error "conversion from pointer type" }
 }