https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83215
Bug ID: 83215
Summary: C++: struct with char-array assumed to alias with
everything
Product: gcc
Version: 8.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: dominik.infuehr at gmail dot com
Target Milestone: ---
TBAA seems to be more conservative for C++ in the following example since GCC
7:
struct mytest {
float a;
#ifdef WITH_BUFFER
char buf[256];
#endif
};
int foo(mytest *m, int *i) {
int tmp = *i; // first load
m->a = 10.0f;
return tmp + *i; // second load since GCC 7
}
Since GCC 7 this code generates two loads with -DWITH_BUFFER, without buf in
the struct there is just one load. buf isn't touched at all in this function.
This only affects C++-code, not the C-frontend.
TYPE_TYPLESS_STORAGE is set for this struct, aggregates with this flag set are
assumed to alias with everything in gcc/alias.c(get_alias_set).
Seems to be introduced with revision 246866
(https://gcc.gnu.org/viewcvs/gcc?view=revision&revision=246866).
