https://gcc.gnu.org/bugzilla/show_bug.cgi?id=128154
Bug ID: 128154
Summary: gcc.c-torture/execute/20000603-1.c aborts when f() is
not inlined early (IPA-CP and IPA-SRA)
Product: gcc
Version: 16.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: ipa
Assignee: unassigned at gcc dot gnu.org
Reporter: bernie at codewiz dot org
Target Milestone: ---
I hit this while testing m68k-amigaos-gcc, but then I realized it's
reproducible also with my Fedora x86_64 GCC 16.2.1.
gcc.c-torture/execute/20000603-1.c aborts whenever f() reaches the IPA passes
without having been inlined early.
Reduced repro:
```c
struct s1 { double d; };
struct s2 { double d; };
union u { struct s1 x; struct s2 y; };
static __attribute__((noinline)) double f(struct s1 *a, struct s2 *b)
{
a->d = 1.0;
return b->d + 1.0;
}
int main()
{
union u a;
a.x.d = 0.0;
if (f (&a.x, &a.y) != 2.0)
__builtin_abort ();
return 0;
}
```
With gcc 16.2.1 on x86_64, `gcc -O2 t.c && ./a.out` aborts, and main compiles
to a bare `call abort`.
It passes at -O1, with -fno-strict-aliasing, or with both -fno-ipa-cp and
-fno-ipa-sra. Either pass alone is enough to break it:
- IPA-CP propagates the known aggregate value `b->d == 0.0` from the call site,
because the store through `a` (a `struct s1`) is assumed not to clobber the
load through `b` (a `struct s2`).
- IPA-SRA turns `b` into a by-value `double` loaded in main before the call, on
the same assumption.
The unmodified test also aborts with `-O2 -flto -fno-early-inlining` on x86_64:
under LTO f becomes local, and the IPA passes then change it. Without -flto, f
stays global and they leave it alone.
I can't tell if the test is within the bounds of DR#236 or invalid C that
passes by accident in most cases.
