On Mon, Oct 09, 2023 at 04:10:20PM -0400, Jason Merrill wrote:
> On 10/9/23 06:03, Nathaniel Shead wrote:
> > Bootstrapped and regtested on x86_64-pc-linux-gnu with
> > GXX_TESTSUITE_STDS=98,11,14,17,20,23,26,impcx.
> >
> > -- >8 --
> >
> > This patch improves the errors given when casting from void* in C++26 to
> > include the expected type if the type of the pointed-to object was
> > not similar to the casted-to type.
> >
> > It also ensures (for all standard modes) that void* casts are checked
> > even for DECL_ARTIFICIAL declarations, such as lifetime-extended
> > temporaries, and is only ignored for cases where we know it's OK (heap
> > identifiers and source_location::current). This provides more accurate
> > diagnostics when using the pointer and ensures that some other casts
> > from void* are now correctly rejected.
> >
> > gcc/cp/ChangeLog:
> >
> > * constexpr.cc (is_std_source_location_current): New.
> > (cxx_eval_constant_expression): Only ignore cast from void* for
> > specific cases and improve other diagnostics.
> >
> > gcc/testsuite/ChangeLog:
> >
> > * g++.dg/cpp0x/constexpr-cast4.C: New test.
> >
> > Signed-off-by: Nathaniel Shead <nathanielosh...@gmail.com>
> > ---
> > gcc/cp/constexpr.cc | 83 +++++++++++++++++---
> > gcc/testsuite/g++.dg/cpp0x/constexpr-cast4.C | 7 ++
> > 2 files changed, 78 insertions(+), 12 deletions(-)
> > create mode 100644 gcc/testsuite/g++.dg/cpp0x/constexpr-cast4.C
> >
> > diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
> > index 0f948db7c2d..f38d541a662 100644
> > --- a/gcc/cp/constexpr.cc
> > +++ b/gcc/cp/constexpr.cc
> > @@ -2301,6 +2301,36 @@ is_std_allocator_allocate (const constexpr_call
> > *call)
> > && is_std_allocator_allocate (call->fundef->decl));
> > }
> > +/* Return true if FNDECL is std::source_location::current. */
> > +
> > +static inline bool
> > +is_std_source_location_current (tree fndecl)
> > +{
> > + if (!decl_in_std_namespace_p (fndecl))
> > + return false;
> > +
> > + tree name = DECL_NAME (fndecl);
> > + if (name == NULL_TREE || !id_equal (name, "current"))
> > + return false;
> > +
> > + tree ctx = DECL_CONTEXT (fndecl);
> > + if (ctx == NULL_TREE || !CLASS_TYPE_P (ctx) || !TYPE_MAIN_DECL (ctx))
> > + return false;
> > +
> > + name = DECL_NAME (TYPE_MAIN_DECL (ctx));
> > + return name && id_equal (name, "source_location");
> > +}
> > +
> > +/* Overload for the above taking constexpr_call*. */
> > +
> > +static inline bool
> > +is_std_source_location_current (const constexpr_call *call)
> > +{
> > + return (call
> > + && call->fundef
> > + && is_std_source_location_current (call->fundef->decl));
> > +}
> > +
> > /* Return true if FNDECL is __dynamic_cast. */
> > static inline bool
> > @@ -7850,33 +7880,62 @@ cxx_eval_constant_expression (const constexpr_ctx
> > *ctx, tree t,
> > if (TYPE_PTROB_P (type)
> > && TYPE_PTR_P (TREE_TYPE (op))
> > && VOID_TYPE_P (TREE_TYPE (TREE_TYPE (op)))
> > - /* Inside a call to std::construct_at or to
> > - std::allocator<T>::{,de}allocate, we permit casting from void*
> > + /* Inside a call to std::construct_at,
> > + std::allocator<T>::{,de}allocate, or
> > + std::source_location::current, we permit casting from void*
> > because that is compiler-generated code. */
> > && !is_std_construct_at (ctx->call)
> > - && !is_std_allocator_allocate (ctx->call))
> > + && !is_std_allocator_allocate (ctx->call)
> > + && !is_std_source_location_current (ctx->call))
> > {
> > /* Likewise, don't error when casting from void* when OP is
> > &heap uninit and similar. */
> > tree sop = tree_strip_nop_conversions (op);
> > - if (TREE_CODE (sop) == ADDR_EXPR
> > - && VAR_P (TREE_OPERAND (sop, 0))
> > - && DECL_ARTIFICIAL (TREE_OPERAND (sop, 0)))
> > + tree decl = NULL_TREE;
> > + if (TREE_CODE (sop) == ADDR_EXPR)
> > + decl = TREE_OPERAND (sop, 0);
> > + if (decl
> > + && VAR_P (decl)
> > + && DECL_ARTIFICIAL (decl)
> > + && (DECL_NAME (decl) == heap_identifier
> > + || DECL_NAME (decl) == heap_uninit_identifier
> > + || DECL_NAME (decl) == heap_vec_identifier
> > + || DECL_NAME (decl) == heap_vec_uninit_identifier))
> > /* OK */;
> > /* P2738 (C++26): a conversion from a prvalue P of type "pointer to
> > cv void" to a pointer-to-object type T unless P points to an
> > object whose type is similar to T. */
> > - else if (cxx_dialect > cxx23
> > - && (sop = cxx_fold_indirect_ref (ctx, loc,
> > - TREE_TYPE (type), sop)))
> > + else if (cxx_dialect > cxx23)
> > {
> > - r = build1 (ADDR_EXPR, type, sop);
> > - break;
> > + r = cxx_fold_indirect_ref (ctx, loc, TREE_TYPE (type), sop);
> > + if (r)
> > + {
> > + r = build1 (ADDR_EXPR, type, r);
> > + break;
> > + }
> > + if (!ctx->quiet)
> > + {
> > + if (TREE_CODE (sop) == ADDR_EXPR)
> > + {
> > + error_at (loc, "cast from %qT is not allowed because "
> > + "pointed-to type %qT is not similar to %qT",
> > + TREE_TYPE (op), TREE_TYPE (TREE_TYPE (sop)),
> > + TREE_TYPE (type));
> > + tree obj = build_fold_indirect_ref (sop);
> > + inform (DECL_SOURCE_LOCATION (obj),
> > + "pointed-to object declared here");
> > + }
> > + else
> > + error_at (loc, "cast from %qT is not allowed",
>
> Can this be more helpful as well, i.e. say because op is not the address of
> an object of similar type?
>
> Can we only get here if op is null, since we would have returned already for
> non-constant op?
>
> Jason
>
Hm, yes; I'd kept the error as it was because I wasn't sure what other
kinds of trees might end up here, but I've done a fair amount of testing
and I've only been able to reach here with null pointers: everything
else gets caught earlier. I've updated the error message appropriately
and documented this assumption with an assertion.
Bootstrapped + regtested on x86_64-pc-linux-gnu as above.
-- >8 --
This patch improves the errors given when casting from void* in C++26 to
include the expected type if the types of the pointed-to objects were
not similar. It also ensures (for all standard modes) that void* casts
are checked even for DECL_ARTIFICIAL declarations, such as
lifetime-extended temporaries, and is only ignored for cases where we
know it's OK (e.g. source_location::current) or have no other choice
(heap-allocated data).
gcc/cp/ChangeLog:
* constexpr.cc (is_std_source_location_current): New.
(cxx_eval_constant_expression): Only ignore cast from void* for
specific cases and improve other diagnostics.
gcc/testsuite/ChangeLog:
* g++.dg/cpp0x/constexpr-cast4.C: New test.
Signed-off-by: Nathaniel Shead <nathanielosh...@gmail.com>
---
gcc/cp/constexpr.cc | 87 +++++++++++++++++---
gcc/testsuite/g++.dg/cpp0x/constexpr-cast4.C | 11 +++
2 files changed, 86 insertions(+), 12 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp0x/constexpr-cast4.C
diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index 0f948db7c2d..d060e374cb3 100644
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -2301,6 +2301,36 @@ is_std_allocator_allocate (const constexpr_call *call)
&& is_std_allocator_allocate (call->fundef->decl));
}
+/* Return true if FNDECL is std::source_location::current. */
+
+static inline bool
+is_std_source_location_current (tree fndecl)
+{
+ if (!decl_in_std_namespace_p (fndecl))
+ return false;
+
+ tree name = DECL_NAME (fndecl);
+ if (name == NULL_TREE || !id_equal (name, "current"))
+ return false;
+
+ tree ctx = DECL_CONTEXT (fndecl);
+ if (ctx == NULL_TREE || !CLASS_TYPE_P (ctx) || !TYPE_MAIN_DECL (ctx))
+ return false;
+
+ name = DECL_NAME (TYPE_MAIN_DECL (ctx));
+ return name && id_equal (name, "source_location");
+}
+
+/* Overload for the above taking constexpr_call*. */
+
+static inline bool
+is_std_source_location_current (const constexpr_call *call)
+{
+ return (call
+ && call->fundef
+ && is_std_source_location_current (call->fundef->decl));
+}
+
/* Return true if FNDECL is __dynamic_cast. */
static inline bool
@@ -7850,33 +7880,66 @@ cxx_eval_constant_expression (const constexpr_ctx *ctx,
tree t,
if (TYPE_PTROB_P (type)
&& TYPE_PTR_P (TREE_TYPE (op))
&& VOID_TYPE_P (TREE_TYPE (TREE_TYPE (op)))
- /* Inside a call to std::construct_at or to
- std::allocator<T>::{,de}allocate, we permit casting from void*
+ /* Inside a call to std::construct_at,
+ std::allocator<T>::{,de}allocate, or
+ std::source_location::current, we permit casting from void*
because that is compiler-generated code. */
&& !is_std_construct_at (ctx->call)
- && !is_std_allocator_allocate (ctx->call))
+ && !is_std_allocator_allocate (ctx->call)
+ && !is_std_source_location_current (ctx->call))
{
/* Likewise, don't error when casting from void* when OP is
&heap uninit and similar. */
tree sop = tree_strip_nop_conversions (op);
- if (TREE_CODE (sop) == ADDR_EXPR
- && VAR_P (TREE_OPERAND (sop, 0))
- && DECL_ARTIFICIAL (TREE_OPERAND (sop, 0)))
+ tree decl = NULL_TREE;
+ if (TREE_CODE (sop) == ADDR_EXPR)
+ decl = TREE_OPERAND (sop, 0);
+ if (decl
+ && VAR_P (decl)
+ && DECL_ARTIFICIAL (decl)
+ && (DECL_NAME (decl) == heap_identifier
+ || DECL_NAME (decl) == heap_uninit_identifier
+ || DECL_NAME (decl) == heap_vec_identifier
+ || DECL_NAME (decl) == heap_vec_uninit_identifier))
/* OK */;
/* P2738 (C++26): a conversion from a prvalue P of type "pointer to
cv void" to a pointer-to-object type T unless P points to an
object whose type is similar to T. */
- else if (cxx_dialect > cxx23
- && (sop = cxx_fold_indirect_ref (ctx, loc,
- TREE_TYPE (type), sop)))
+ else if (cxx_dialect > cxx23)
{
- r = build1 (ADDR_EXPR, type, sop);
- break;
+ r = cxx_fold_indirect_ref (ctx, loc, TREE_TYPE (type), sop);
+ if (r)
+ {
+ r = build1 (ADDR_EXPR, type, r);
+ break;
+ }
+ if (!ctx->quiet)
+ {
+ if (TREE_CODE (sop) == ADDR_EXPR)
+ {
+ error_at (loc, "cast from %qT is not allowed because "
+ "pointed-to type %qT is not similar to %qT",
+ TREE_TYPE (op), TREE_TYPE (TREE_TYPE (sop)),
+ TREE_TYPE (type));
+ tree obj = build_fold_indirect_ref (sop);
+ inform (DECL_SOURCE_LOCATION (obj),
+ "pointed-to object declared here");
+ }
+ else
+ {
+ gcc_assert (integer_zerop (sop));
+ error_at (loc, "cast from %qT is not allowed because "
+ "%qE does not point to an object",
+ TREE_TYPE (op), oldop);
+ }
+ }
+ *non_constant_p = true;
+ return t;
}
else
{
if (!ctx->quiet)
- error_at (loc, "cast from %qT is not allowed",
+ error_at (loc, "cast from %qT is not allowed before C++26",
TREE_TYPE (op));
*non_constant_p = true;
return t;
diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-cast4.C
b/gcc/testsuite/g++.dg/cpp0x/constexpr-cast4.C
new file mode 100644
index 00000000000..cfeaa1ac3bf
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-cast4.C
@@ -0,0 +1,11 @@
+// { dg-do compile { target c++11 } }
+
+constexpr int&& r = 1 + 2; // { dg-message "pointed-to object declared here"
"" { target c++26 } }
+constexpr void* vpr = &r;
+constexpr int* pi = static_cast<int*>(vpr); // { dg-error "cast from
.void\\*. is not allowed" "" { target c++23_down } }
+constexpr float* pf = static_cast<float*>(vpr); // { dg-error "cast from
.void\\*. is not allowed" "" { target c++23_down } }
+// { dg-error "cast from .void\\*. is not allowed because pointed-to type
.int. is not similar to .float." "" { target c++26 } .-1 }
+
+constexpr void* vnp = nullptr;
+constexpr int* pi2 = static_cast<int*>(vnp); // { dg-error "cast from
.void\\*. is not allowed" "" { target c++23_down } }
+// { dg-error "cast from .void\\*. is not allowed because .vnp. does not point
to an object" "" { target c++26 } .-1 }
--
2.42.0
