[Bug target/112929] [14] RISC-V vector: Variable clobbered at runtime

[patrick at rivosinc dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112929

--- Comment #14 from Patrick O'Neill <patrick at rivosinc dot com> ---
I've reproduced the same failure on tip-of-tree using an old QEMU but cannot
reproduce with a freshly built QEMU:
GCC hash: eea25179d8d1406685b8b0995ba841605f895283 (tip-of-tree)
Qemu hash: 78385bc738108a9b5b20e639520dc60425ca2a5a (v8.1.2)
Glibc hash: a704fd9a133bfb10510e18702f48a6a9c88dbbd5 (v2.37)

My QEMU was built with GCC hash: 8b5cd6c4519cc120badd2b35a9e30d4deb82c012
If I use the tip-of-tree to build QMEU the failure does not exist anymore.

Your modified testcase does not produce the failure since it's missing the
variadic function call. Here is a version that works for me and does not use
printf:

int a, l, i, p, q, t, n, o;
int *volatile c;
static int j;
static struct pack_1_struct d;
long e;
char m = 5;
short s;

#pragma pack(1)
struct pack_1_struct {
  long c;
  int d;
  int e;
  int f;
  int g;
  int h;
  int i;
} h, r = {1}, *f = &h, *volatile g;

void add_em_up(int count, ...) {
  __builtin_va_list ap;
  __builtin_va_start(ap, count);
  __builtin_va_end(ap);
}

int main() {
  int u;
  j = 0;

  for (; j < 9; ++j) {
    u = ++t ? a : 0;
    if (u) {
      int *v = &d.d;
      *v = g || e;
      *c = 0;
      *f = h;
    }
    s = l && c;
    o = i;
    d.f || (p = 0);
    q |= n;
  }

  r = *f;

  add_em_up(1, 1);

  if (m != 5)
    return 1;

  return 0;
}

Commands (Note that I used the old QEMU build):
gcv:
> /scratch/tc-testing/tc-dec-11-trunk/build-rv64gcv/bin/riscv64-unknown-linux-gnu-gcc
>  -march=rv64gcv -mabi=lp64d -O3 red.c -o rv64gcv.out
> QEMU_CPU=rv64,vlen=128,v=true,vext_spec=v1.0 
> /scratch/tc-testing/tc-dec-8-trunk/build-rv64gcv/bin/qemu-riscv64 rv64gcv.out
> echo $?
1

gc:
> /scratch/tc-testing/tc-dec-11-trunk/build-rv64gcv/bin/riscv64-unknown-linux-gnu-gcc
>  -march=rv64gc -mabi=lp64d -O3 red.c -o rv64gc.out
> QEMU_CPU=rv64,vlen=128,v=true,vext_spec=v1.0 
> /scratch/tc-testing/tc-dec-8-trunk/build-rv64gcv/bin/qemu-riscv64 rv64gc.out  
>                                                                  
> echo $?
0

I think you're right Robin - it has some interaction with QMEU. The QEMU with
GCC r14-6339-g8b5cd6c4519 produces the error but the QEMU with the tip-of-tree
GCC r14-6417-geea25179d8d does not produce the error.