Tested x86_64-pc-linux-gnu, applying to trunk.
-- 8< --
My change for PR53220 made array to pointer decay for prvalue arrays
ill-formed to catch well-defined C code that produces a dangling pointer in
C++ due to the shorter lifetime of compound literals. This wasn't really
correct, but wasn't a problem until C++17 added prvalue arrays, at which
point it started rejecting valid C++ code.
I wanted to make sure that we still diagnose the problematic code;
-Wdangling-pointer covers the array-lit.c case, but I needed to extend
-Wreturn-local-addr to handle the return case.
PR c++/94264
PR c++/53220
gcc/c/ChangeLog:
* c-typeck.cc (array_to_pointer_conversion): Adjust -Wc++-compat
diagnostic.
gcc/cp/ChangeLog:
* call.cc (convert_like_internal): Remove obsolete comment.
* typeck.cc (decay_conversion): Allow array prvalue.
(maybe_warn_about_returning_address_of_local): Check
for returning pointer to temporary.
gcc/testsuite/ChangeLog:
* c-c++-common/array-lit.c: Adjust.
* g++.dg/cpp1z/array-prvalue1.C: New test.
* g++.dg/ext/complit17.C: New test.
---
gcc/c/c-typeck.cc | 2 +-
gcc/cp/call.cc | 2 --
gcc/cp/typeck.cc | 12 +++---------
gcc/testsuite/c-c++-common/array-lit.c | 3 ++-
gcc/testsuite/g++.dg/cpp1z/array-prvalue1.C | 7 +++++++
gcc/testsuite/g++.dg/ext/complit17.C | 4 ++++
6 files changed, 17 insertions(+), 13 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp1z/array-prvalue1.C
create mode 100644 gcc/testsuite/g++.dg/ext/complit17.C
diff --git a/gcc/c/c-typeck.cc b/gcc/c/c-typeck.cc
index 1dbb4471a88..17fdc9789b4 100644
--- a/gcc/c/c-typeck.cc
+++ b/gcc/c/c-typeck.cc
@@ -1748,7 +1748,7 @@ array_to_pointer_conversion (location_t loc, tree exp)
if (!TREE_READONLY (decl) && !TREE_STATIC (decl))
warning_at (DECL_SOURCE_LOCATION (decl), OPT_Wc___compat,
"converting an array compound literal to a pointer "
- "is ill-formed in C++");
+ "leads to a dangling pointer in C++");
}
adr = build_unary_op (loc, ADDR_EXPR, exp, true);
diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
index 81b104f4b40..ae0decd87f1 100644
--- a/gcc/cp/call.cc
+++ b/gcc/cp/call.cc
@@ -8578,8 +8578,6 @@ convert_like_internal (conversion *convs, tree expr, tree
fn, int argnum,
array = finish_compound_literal (array, new_ctor, complain);
/* This is dubious now, should be blessed by P2752. */
DECL_MERGEABLE (TARGET_EXPR_SLOT (array)) = true;
- /* Take the address explicitly rather than via decay_conversion
- to avoid the error about taking the address of a temporary. */
array = cp_build_addr_expr (array, complain);
}
else
diff --git a/gcc/cp/typeck.cc b/gcc/cp/typeck.cc
index e995fb6ddd7..0839d0a4167 100644
--- a/gcc/cp/typeck.cc
+++ b/gcc/cp/typeck.cc
@@ -2534,15 +2534,6 @@ decay_conversion (tree exp,
return error_mark_node;
}
- /* Don't let an array compound literal decay to a pointer. It can
- still be used to initialize an array or bind to a reference. */
- if (TREE_CODE (exp) == TARGET_EXPR)
- {
- if (complain & tf_error)
- error_at (loc, "taking address of temporary array");
- return error_mark_node;
- }
-
ptrtype = build_pointer_type (TREE_TYPE (type));
if (VAR_P (exp))
@@ -10535,6 +10526,9 @@ maybe_warn_about_returning_address_of_local (tree
retval, location_t loc)
if (TYPE_REF_P (valtype))
warning_at (loc, OPT_Wreturn_local_addr,
"returning reference to temporary");
+ else if (TYPE_PTR_P (valtype))
+ warning_at (loc, OPT_Wreturn_local_addr,
+ "returning pointer to temporary");
else if (is_std_init_list (valtype))
warning_at (loc, OPT_Winit_list_lifetime,
"returning temporary %<initializer_list%> does not extend "
diff --git a/gcc/testsuite/c-c++-common/array-lit.c
b/gcc/testsuite/c-c++-common/array-lit.c
index 6505c2091b4..a6b3adf7cc8 100644
--- a/gcc/testsuite/c-c++-common/array-lit.c
+++ b/gcc/testsuite/c-c++-common/array-lit.c
@@ -1,10 +1,11 @@
/* { dg-options "-std=c99 -Wc++-compat -Werror" { target c } } */
+/* { dg-options "-Werror=dangling-pointer=1" { target c++ } } */
/* { dg-prune-output "treated as errors" } */
#include <stdio.h>
int main()
{
- for (int *p = (int[]){ 1, 2, 3, 0 }; /* { dg-error "array" } */
+ for (int *p = (int[]){ 1, 2, 3, 0 }; /* { dg-error "array|temporary" } */
*p; ++p) {
printf("%d\n", *p);
}
diff --git a/gcc/testsuite/g++.dg/cpp1z/array-prvalue1.C
b/gcc/testsuite/g++.dg/cpp1z/array-prvalue1.C
new file mode 100644
index 00000000000..e837d3253a1
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/array-prvalue1.C
@@ -0,0 +1,7 @@
+// PR c++/94264
+// { dg-do compile { target c++17 } }
+
+int main() {
+ using T = int[];
+ T{1, 2} == nullptr;
+}
diff --git a/gcc/testsuite/g++.dg/ext/complit17.C
b/gcc/testsuite/g++.dg/ext/complit17.C
new file mode 100644
index 00000000000..acc80847be3
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ext/complit17.C
@@ -0,0 +1,4 @@
+// PR c++/53220
+// { dg-options "" }
+
+int* f() { return (int[]){42}; } // { dg-warning "pointer to temporary" }
base-commit: 7eaf95689bf495ab07473951ededa835eb618123
--
2.39.3
