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| author | Marek Polacek <polacek@redhat.com> | 2023-10-19 16:32:10 -0400 |
|---|---|---|
| committer | Marek Polacek <polacek@redhat.com> | 2023-10-20 15:32:53 -0400 |
| commit | 281699fbff6262766674ab13087d37db751cd40a (patch) | |
| tree | 10f1a33e86ffeaec494812e4f3c03e7195494869 | |
| parent | a663fe63889db486d577b20aff0730034400bfe9 (diff) | |
| download | gcc-281699fbff6262766674ab13087d37db751cd40a.zip gcc-281699fbff6262766674ab13087d37db751cd40a.tar.gz gcc-281699fbff6262766674ab13087d37db751cd40a.tar.bz2 | |
c-family: char8_t and aliasing in C vs C++ [PR111884]
In the PR, Joseph says that in C char8_t is not a distinct type. So
we should behave as if it can alias anything, like ordinary char.
In C, unsigned_char_type_node == char8_type_node, so with this patch
we return 0 instead of -1. And the following comment says:
/* The C standard guarantees that any object may be accessed via an
lvalue that has narrow character type (except char8_t). */
if (t == char_type_node
|| t == signed_char_type_node
|| t == unsigned_char_type_node)
return 0;
Which appears to be wrong, so I'm adjusting that as well.
PR c/111884
gcc/c-family/ChangeLog:
* c-common.cc (c_common_get_alias_set): Return -1 for char8_t only
in C++.
gcc/testsuite/ChangeLog:
* c-c++-common/alias-1.c: New test.
| -rw-r--r-- | gcc/c-family/c-common.cc | 7 | ||||
| -rw-r--r-- | gcc/testsuite/c-c++-common/alias-1.c | 23 |
2 files changed, 27 insertions, 3 deletions
diff --git a/gcc/c-family/c-common.cc b/gcc/c-family/c-common.cc index f044db5..0efdc67 100644 --- a/gcc/c-family/c-common.cc +++ b/gcc/c-family/c-common.cc @@ -3828,12 +3828,13 @@ c_common_get_alias_set (tree t) if (!TYPE_P (t)) return -1; - /* Unlike char, char8_t doesn't alias. */ - if (flag_char8_t && t == char8_type_node) + /* Unlike char, char8_t doesn't alias in C++. (In C, char8_t is not + a distinct type.) */ + if (flag_char8_t && t == char8_type_node && c_dialect_cxx ()) return -1; /* The C standard guarantees that any object may be accessed via an - lvalue that has narrow character type (except char8_t). */ + lvalue that has narrow character type. */ if (t == char_type_node || t == signed_char_type_node || t == unsigned_char_type_node) diff --git a/gcc/testsuite/c-c++-common/alias-1.c b/gcc/testsuite/c-c++-common/alias-1.c new file mode 100644 index 0000000..d72fec4 --- /dev/null +++ b/gcc/testsuite/c-c++-common/alias-1.c @@ -0,0 +1,23 @@ +/* PR c/111884 */ +/* { dg-do compile } */ +/* { dg-options "-O2 -Wall" } */ +/* { dg-additional-options "-std=c++20" { target c++ } } */ +/* { dg-additional-options "-std=c2x" { target c } } */ + +int f(int i) +{ + int f = 1; + return i[(unsigned char *)&f]; +} + +int g(int i) +{ + int f = 1; + return i[(signed char *)&f]; +} + +int h(int i) +{ + int f = 1; + return i[(char *)&f]; +} |