Re: [PATCH v2] c++: Fall through for arrays of T vs T cv [PR104996]

[Jason Merrill via Gcc-patches]

On 4/18/22 18:09, Ed Catmur wrote:

If two arrays do not have the exact same element type including qualification, this could 
be e.g. f(int (&&)[]) vs. f(int const (&)[]), which can still be distinguished 
by the lvalue-rvalue tiebreaker.

By tightening this branch (in accordance with the letter of the Standard) we 
fall through to the next branch, which tests whether they have different 
element type ignoring qualification and returns 0 in that case; thus we only 
actually fall through in the T[...] vs. T cv[...] case, eventually considering 
the lvalue-rvalue tiebreaker at the end of compare_ics.

Bootstrapped and tested on x86_64-pc-linux-gnu.

Signed-off-by: Ed Catmur 


Applied, thanks.


PR c++/104996

gcc/cp/ChangeLog:

* call.cc (compare_ics): When comparing list-initialization sequences, 
do not return early.

gcc/testsuite/ChangeLog:

* g++.dg/cpp0x/initlist129.C: New test.
---
  gcc/cp/call.cc   | 7 ++-
  gcc/testsuite/g++.dg/cpp0x/initlist129.C | 6 ++
  2 files changed, 8 insertions(+), 5 deletions(-)
  create mode 100644 gcc/testsuite/g++.dg/cpp0x/initlist129.C

diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
index 51d8f6c3fb1..fa18d7f8f9d 100644
--- a/gcc/cp/call.cc
+++ b/gcc/cp/call.cc
@@ -11546,12 +11546,9 @@ compare_ics (conversion *ics1, conversion *ics2)
 P0388R4.)  */
else if (t1->kind == ck_aggr
   && TREE_CODE (t1->type) == ARRAY_TYPE
-  && TREE_CODE (t2->type) == ARRAY_TYPE)
+  && TREE_CODE (t2->type) == ARRAY_TYPE
+  && same_type_p (TREE_TYPE (t1->type), TREE_TYPE (t2->type)))
{
- /* The type of the array elements must be the same.  */
- if (!same_type_p (TREE_TYPE (t1->type), TREE_TYPE (t2->type)))
-   return 0;
-
  tree n1 = nelts_initialized_by_list_init (t1);
  tree n2 = nelts_initialized_by_list_init (t2);
  if (tree_int_cst_lt (n1, n2))
diff --git a/gcc/testsuite/g++.dg/cpp0x/initlist129.C 
b/gcc/testsuite/g++.dg/cpp0x/initlist129.C
new file mode 100644
index 000..4d4faa9e08d
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/initlist129.C
@@ -0,0 +1,6 @@
+// PR c++/104996
+// { dg-do compile { target c++11 } }
+
+template char f(int (&&)[size]);
+template int f(int const (&)[size]);
+static_assert(sizeof(f({1, 2, 3})) == 1, "");

[PATCH v2] c++: Fall through for arrays of T vs T cv [PR104996]

[Ed Catmur]

If two arrays do not have the exact same element type including qualification, 
this could be e.g. f(int (&&)[]) vs. f(int const (&)[]), which can still be 
distinguished by the lvalue-rvalue tiebreaker.

By tightening this branch (in accordance with the letter of the Standard) we 
fall through to the next branch, which tests whether they have different 
element type ignoring qualification and returns 0 in that case; thus we only 
actually fall through in the T[...] vs. T cv[...] case, eventually considering 
the lvalue-rvalue tiebreaker at the end of compare_ics.

Bootstrapped and tested on x86_64-pc-linux-gnu.

Signed-off-by: Ed Catmur 

PR c++/104996

gcc/cp/ChangeLog:

* call.cc (compare_ics): When comparing list-initialization sequences, 
do not return early.

gcc/testsuite/ChangeLog:

* g++.dg/cpp0x/initlist129.C: New test.
---
 gcc/cp/call.cc   | 7 ++-
 gcc/testsuite/g++.dg/cpp0x/initlist129.C | 6 ++
 2 files changed, 8 insertions(+), 5 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp0x/initlist129.C

diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
index 51d8f6c3fb1..fa18d7f8f9d 100644
--- a/gcc/cp/call.cc
+++ b/gcc/cp/call.cc
@@ -11546,12 +11546,9 @@ compare_ics (conversion *ics1, conversion *ics2)
 P0388R4.)  */
   else if (t1->kind == ck_aggr
   && TREE_CODE (t1->type) == ARRAY_TYPE
-  && TREE_CODE (t2->type) == ARRAY_TYPE)
+  && TREE_CODE (t2->type) == ARRAY_TYPE
+  && same_type_p (TREE_TYPE (t1->type), TREE_TYPE (t2->type)))
{
- /* The type of the array elements must be the same.  */
- if (!same_type_p (TREE_TYPE (t1->type), TREE_TYPE (t2->type)))
-   return 0;
-
  tree n1 = nelts_initialized_by_list_init (t1);
  tree n2 = nelts_initialized_by_list_init (t2);
  if (tree_int_cst_lt (n1, n2))
diff --git a/gcc/testsuite/g++.dg/cpp0x/initlist129.C 
b/gcc/testsuite/g++.dg/cpp0x/initlist129.C
new file mode 100644
index 000..4d4faa9e08d
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/initlist129.C
@@ -0,0 +1,6 @@
+// PR c++/104996
+// { dg-do compile { target c++11 } }
+
+template char f(int (&&)[size]);
+template int f(int const (&)[size]);
+static_assert(sizeof(f({1, 2, 3})) == 1, "");
-- 
2.30.2