On 10/20/23 12:31, Marek Polacek wrote:
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
OK.
-- >8 -- 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. --- gcc/c-family/c-common.cc | 7 ++++--- gcc/testsuite/c-c++-common/alias-1.c | 23 +++++++++++++++++++++++ 2 files changed, 27 insertions(+), 3 deletions(-) create mode 100644 gcc/testsuite/c-c++-common/alias-1.c diff --git a/gcc/c-family/c-common.cc b/gcc/c-family/c-common.cc index f044db5b797..0efdc677217 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 00000000000..d72fec47f76 --- /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]; +} base-commit: eb15fad3190a8b33e3e451b964ff1ecf08bbb113
