[PATCH] PR c++/80544 strip cv-quals from cast results

[Jonathan Wakely]

Ping for https://gcc.gnu.org/ml/gcc-patches/2017-04/msg01414.html ...

On 27/04/17 17:59 +0100, Jonathan Wakely wrote:
>This is probably not the best way to do this, but it seems to work.
>
>I also tried to add a warning like EDG's (see the PR) but it gave a
>false positive for direct-list-init of scoped enums (P0138R2, r240449)
>because that code goes through build_c_cast to perform the conversion,
>so looks like a cast to my new warning.
>
>Tested x86_64-linux, OK for trunk?
>
>
>gcc/cp:
>
>	PR c++/80544
>	* typeck.c (build_static_cast_1, build_reinterpret_cast_1)
>	(build_const_cast_1): Strip cv-quals from non-class prvalue results.
>
>gcc/testsuite:
>
>	PR c++/80544
>	* g++.dg/expr/cast11.C: New test.
>
>

>commit 47763f3c84de86dd1ebbaac73e341e2de9b5be68
>Author: Jonathan Wakely <jwakely@redhat.com>
>Date:   Thu Apr 27 16:49:25 2017 +0100
>
>    PR c++/80544 strip cv-quals from cast results
>    
>    gcc/cp:
>    
>    	PR c++/80544
>    	* typeck.c (build_static_cast_1, build_reinterpret_cast_1)
>    	(build_const_cast_1): Strip cv-quals from non-class prvalue results.
>    
>    gcc/testsuite:
>    
>    	PR c++/80544
>    	* g++.dg/expr/cast11.C: New test.
>
>diff --git a/gcc/cp/typeck.c b/gcc/cp/typeck.c
>index 7aee0d6..e41b335 100644
>--- a/gcc/cp/typeck.c
>+++ b/gcc/cp/typeck.c
>@@ -6708,6 +6708,10 @@ build_static_cast_1 (tree type, tree expr, bool c_cast_p,
>   /* Save casted types in the function's used types hash table.  */
>   used_types_insert (type);
> 
>+  /* A prvalue of non-class type is cv-unqualified.  */
>+  if (TREE_CODE (type) != REFERENCE_TYPE && !CLASS_TYPE_P (type))
>+    type = cv_unqualified (type);
>+
>   /* [expr.static.cast]
> 
>      An lvalue of type "cv1 B", where B is a class type, can be cast
>@@ -7070,6 +7074,10 @@ build_reinterpret_cast_1 (tree type, tree expr, bool c_cast_p,
>   /* Save casted types in the function's used types hash table.  */
>   used_types_insert (type);
> 
>+  /* A prvalue of non-class type is cv-unqualified.  */
>+  if (TREE_CODE (type) != REFERENCE_TYPE && !CLASS_TYPE_P (type))
>+    type = cv_unqualified (type);
>+
>   /* [expr.reinterpret.cast]
>      An lvalue expression of type T1 can be cast to the type
>      "reference to T2" if an expression of type "pointer to T1" can be
>@@ -7300,6 +7308,10 @@ build_const_cast_1 (tree dst_type, tree expr, tsubst_flags_t complain,
>   /* Save casted types in the function's used types hash table.  */
>   used_types_insert (dst_type);
> 
>+  /* A prvalue of non-class type is cv-unqualified.  */
>+  if (TREE_CODE (dst_type) != REFERENCE_TYPE && !CLASS_TYPE_P (dst_type))
>+    dst_type = cv_unqualified (dst_type);
>+
>   src_type = TREE_TYPE (expr);
>   /* Expressions do not really have reference types.  */
>   if (TREE_CODE (src_type) == REFERENCE_TYPE)
>diff --git a/gcc/testsuite/g++.dg/expr/cast11.C b/gcc/testsuite/g++.dg/expr/cast11.C
>new file mode 100644
>index 0000000..642087e
>--- /dev/null
>+++ b/gcc/testsuite/g++.dg/expr/cast11.C
>@@ -0,0 +1,34 @@
>+// { dg-do compile { target c++11 } }
>+// c++/80544 cast expressions returned cv-qualified prvalues
>+
>+template<typename T> void f(T&&) { }
>+template<typename T> void f(T const&&) = delete;
>+
>+template<typename T> void g(T&&) = delete;
>+template<typename T> void g(T const&&) { }
>+
>+struct B { int i; } b;
>+
>+void f1()
>+{
>+  int i = 0;
>+  f((long const)i);
>+  f((int* const)&i);
>+  f((int const* const)&i);
>+  f((long* const)&i);
>+
>+  f(static_cast<long const>(i));
>+  f(reinterpret_cast<long const>(&i));
>+
>+  f(static_cast<int* const>(&i));
>+  f(const_cast<int* const>(&i));
>+  f(reinterpret_cast<long* const>(&i));
>+
>+  using ptrmem = int B::*;
>+  f(static_cast<ptrmem const>(&B::i));
>+  f(const_cast<ptrmem const>(&B::i));
>+  f(reinterpret_cast<ptrmem const>(&B::i));
>+
>+  // prvalue of class type can have cv-quals:
>+  g(static_cast<const B>(b));
>+}