On 3/30/20 3:58 PM, Patrick Palka wrote:
On Thu, 26 Mar 2020, Jason Merrill wrote:
On 3/22/20 9:21 PM, Patrick Palka wrote:
This patch relaxes an assertion in tsubst_default_argument that exposes a
latent
bug in how we substitute an array type into a cv-qualified wildcard function
parameter type. Concretely, the latent bug is that given the function
template
template<typename T> void foo(const T t);
one would expect the type of foo<int[]> to be void(const int*), but we
(seemingly prematurely) strip function parameter types of their top-level
cv-qualifiers when building the function's TYPE_ARG_TYPES, and instead end
up
obtaining void(int*) as the type of foo<int[]> after substitution and
decaying.
We still however correctly substitute into and decay the formal parameter
type,
obtaining const int* as the type of t after substitution. But this then
leads
to us tripping over the assert in tsubst_default_argument that verifies the
formal parameter type and the function type are consistent.
Assuming it's too late at this stage to fix the substitution bug, we can
still
relax the assertion like so. Tested on x86_64-pc-linux-gnu, does this look
OK?
This is core issues 1001/1322, which have not been resolved. Clang does the
substitution the way you suggest; EDG rejects the testcase because the two
substitutions produce different results. I think it would make sense to
follow the EDG behavior until this issue is actually resolved.
Here is what I have so far towards that end. When substituting into the
PARM_DECLs of a function decl, we now additionally check if the
aforementioned Core issues are relevant and issue a (fatal) diagnostic
if so. This patch checks this in tsubst_decl <case PARM_DECL> rather
than in tsubst_function_decl for efficiency reasons, so that we don't
have to perform another traversal over the DECL_ARGUMENTS /
TYPE_ARG_TYPES just to implement this check.
Hmm, this seems like writing more complicated code for a very marginal
optimization; how many function templates have so many parameters that
walking over them once to compare types will have any effect on compile
time?
Is something like this what you have in mind?
-- >8 --
Subject: [PATCH] c++: Reject some instantiations that depend on resolution of
Core issues 1001/1322
gcc/cp/ChangeLog:
Core issues 1001 and 1322
PR c++/92010
* pt.c (tsubst_decl) <case PARM_DECL>: Detect and reject the case where
the function type depends on whether we strip top-level qualifiers from
the type of T before or after substitution.
gcc/testsuite/ChangeLog:
Core issues 1001 and 1322
PR c++/92010
* g++.dg/template/array33.C: New test.
* g++.dg/template/array34.C: New test.
---
gcc/cp/pt.c | 70 ++++++++++++++++++++++++-
gcc/testsuite/g++.dg/template/array33.C | 39 ++++++++++++++
gcc/testsuite/g++.dg/template/array34.C | 63 ++++++++++++++++++++++
3 files changed, 171 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/g++.dg/template/array33.C
create mode 100644 gcc/testsuite/g++.dg/template/array34.C
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 8564eb11df4..fd99053df36 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -14072,9 +14072,77 @@ tsubst_decl (tree t, tree args, tsubst_flags_t
complain)
/* We're dealing with a normal parameter. */
type = tsubst (TREE_TYPE (t), args, complain, in_decl);
+ const int type_quals = cp_type_quals (type);
+
+ /* Determine whether the function type after substitution into the
+ type of the function parameter T depends on the resolution of
+ Core issues 1001/1322, which have not been resolved. In
+ particular, the following detects the case where the resulting
+ function type depends on whether we strip top-level qualifiers
+ from the type of T before or after substitution.
+
+ This can happen only when the dependent type of T is a
+ cv-qualified wildcard type, and substitution yields a
+ (cv-qualified) array type before array-to-pointer conversion. */
+ tree unqual_expanded_types = NULL_TREE;
+ if (TREE_CODE (type) == ARRAY_TYPE
+ && (type_quals & (TYPE_QUAL_CONST|TYPE_QUAL_VOLATILE))
+ && DECL_FUNCTION_SCOPE_P (t)
+ && !DECL_TEMPLATE_PARM_P (t))
+ {
+ tree type_pattern = (PACK_EXPANSION_P (TREE_TYPE (t))
+ ? PACK_EXPANSION_PATTERN (TREE_TYPE (t))
+ : TREE_TYPE (t));
+ if (WILDCARD_TYPE_P (type_pattern)
+ && cv_qualified_p (type_pattern))
+ {
+ /* Substitute into the corresponding wildcard type that is
+ stripped of its own top-level cv-qualifiers. */
+ tree unqual_type;
+ if (PACK_EXPANSION_P (TREE_TYPE (t)))
+ {
+ if (unqual_expanded_types == NULL_TREE)
+ {
+ tree unqual_pack_expansion
+ = copy_node (TREE_TYPE (t));
+ PACK_EXPANSION_PATTERN (unqual_pack_expansion)
+ = cv_unqualified (type_pattern);
+ unqual_expanded_types
+ = tsubst_pack_expansion (unqual_pack_expansion,
+ args, tf_none, in_decl);
+ }
+ unqual_type = TREE_VEC_ELT (unqual_expanded_types, i);
+ }
+ else
+ {
+ tree unqual_type_pattern = cv_unqualified
(type_pattern);
+ unqual_type = tsubst (unqual_type_pattern, args,
+ tf_none, in_decl);
+ }
+ /* Check if the top-level cv-qualifiers on the wildcard type
+ make a difference in the resulting type. */
+ int unqual_type_quals = cp_type_quals (unqual_type);
+ if (type_quals & ~unqual_type_quals
+ & (TYPE_QUAL_CONST|TYPE_QUAL_VOLATILE))
+ {
+ sorry ("the type of function %qD after substitution "
+ "depends on the resolution of Core issues "
+ "1001 and 1332",
+ DECL_NAME (DECL_CONTEXT (t)));
+ if (PACK_EXPANSION_P (TREE_TYPE (t)))
+ inform (input_location, "when substituting into the "
+ "function parameter pack %q#D", t);
+ else
+ inform (input_location, "when substituting into the "
+ "function parameter %q#D", t);
+ type = error_mark_node;
+ }
+ }
+ }
+
type = type_decays_to (type);
TREE_TYPE (r) = type;
- cp_apply_type_quals_to_decl (cp_type_quals (type), r);
+ cp_apply_type_quals_to_decl (type_quals, r);
if (DECL_INITIAL (r))
{
diff --git a/gcc/testsuite/g++.dg/template/array33.C
b/gcc/testsuite/g++.dg/template/array33.C
new file mode 100644
index 00000000000..20b005bc865
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/array33.C
@@ -0,0 +1,39 @@
+// Reject some instantiations whose result depend on the resolution of //
+// Core issues 1001 and 1332, which are not yet resolved.
+// { dg-do compile }
+// { dg-additional-options "-Wno-volatile" }
+
+template<typename T>
+void foo0(T t = 0); // { dg-bogus "" }
+
+template<typename T>
+void foo1(const T = 0); // { dg-message "sorry,
unimplemented" }
+
+template<typename T>
+void foo2(volatile T t = 0); // { dg-message "sorry, unimplemented" }
+
+template<typename T>
+void foo3(const volatile T t = 0); // { dg-message "sorry, unimplemented" }
+
+int main()
+{
+ foo0<char[]>(); // { dg-bogus "" }
+ foo0<const char[]>(); // { dg-bogus "" }
+ foo0<volatile char[]>(); // { dg-bogus "" }
+ foo0<const volatile char[]>(); // { dg-bogus "" }
+
+ foo1<char[]>(); // { dg-message "required from here" }
+ foo1<const char[]>(); // { dg-bogus "" }
+ foo1<volatile char[]>(); // { dg-message "required from here" }
+ foo1<const volatile char[]>(); // { dg-bogus "" }
+
+ foo2<char[]>(); // { dg-message "required from here" }
+ foo2<const char[]>(); // { dg-message "required from here" }
+ foo2<volatile char[]>(); // { dg-bogus "" }
+ foo2<const volatile char[]>(); // { dg-bogus "" }
+
+ foo3<char[]>(); // { dg-message "required from here" }
+ foo3<const char[]>(); // { dg-message "required from here" }
+ foo3<volatile char[]>(); // { dg-message "required from here" }
+ foo3<const volatile char[]>(); // { dg-bogus "" }
+}
diff --git a/gcc/testsuite/g++.dg/template/array34.C
b/gcc/testsuite/g++.dg/template/array34.C
new file mode 100644
index 00000000000..316ea2f6407
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/array34.C
@@ -0,0 +1,63 @@
+// Reject some instantiations whose result depend on the resolution of
+// Core issues 1001 and 1332, which are not yet resolved.
+// { dg-do compile { target c++11 } }
+// { dg-additional-options "-Wno-volatile" }
+
+template<typename... Ts>
+void foo0(Ts... t); // { dg-bogus "" }
+
+template<typename... Ts>
+void foo1(const Ts... t); // { dg-message "sorry, unimplemented" }
+
+template<typename... Ts>
+void foo2(volatile Ts... t); // { dg-message "sorry, unimplemented" }
+
+template<typename... Ts>
+void foo3(const volatile Ts... t); // { dg-message "sorry, unimplemented" }
+
+template<typename... Ts>
+void bar0()
+{
+ foo0<int, Ts..., int>(0, 0, 0);
+}
+
+template<typename... Ts>
+void bar1()
+{
+ foo1<int, Ts..., int>(0, 0, 0);
+}
+
+template<typename... Ts>
+void bar2()
+{
+ foo2<int, Ts..., int>(0, 0, 0);
+}
+
+template<typename... Ts>
+void bar3()
+{
+ foo3<int, Ts..., int>(0, 0, 0);
+}
+
+int main()
+{
+ bar0<char[]>(); // { dg-bogus "" }
+ bar0<const char[]>(); // { dg-bogus "" }
+ bar0<volatile char[]>(); // { dg-bogus "" }
+ bar0<const volatile char[]>(); // { dg-bogus "" }
+
+ bar1<char[]>(); // { dg-message "required from here" }
+ bar1<const char[]>(); // { dg-bogus "" }
+ bar1<volatile char[]>(); // { dg-message "required from here" }
+ bar1<const volatile char[]>(); // { dg-bogus "" }
+
+ bar2<char[]>(); // { dg-message "required from here" }
+ bar2<const char[]>(); // { dg-message "required from here" }
+ bar2<volatile char[]>(); // { dg-bogus "" }
+ bar2<const volatile char[]>(); // { dg-bogus "" }
+
+ bar3<char[]>(); // { dg-message "required from here" }
+ bar3<const char[]>(); // { dg-message "required from here" }
+ bar3<volatile char[]>(); // { dg-message "required from here" }
+ bar3<const volatile char[]>(); // { dg-bogus "" }
+}
