[RISCV] Miscompile with -O3

[dtcxzyw]

Reduced test case:

#include "csmith.h"
uint8_t a = 55;
int32_t b;
int32_t c[4];
uint32_t e[4];
void f() {
  int32_t *o = &c[1];
  *o = 223;
  if (safe_mod_func_uint8_t_u_u(safe_sub_func_uint8_t_u_u(b, 1), a |= *o)) {
    e[0] = ++a;
  }
}
int main() {
  b = 0;
  f();
  printf("%d\n", a);
  return 0;
}

> bin/clang -O0 --target=riscv64-linux-gnu test.c -I/usr/include/csmith -w
> qemu-riscv64 -L /usr/riscv64-linux-gnu/ a.out
255
> bin/clang -O3 --target=riscv64-linux-gnu test.c -I/usr/include/csmith -w
> qemu-riscv64 -L /usr/riscv64-linux-gnu/ a.out
224

llvm version: d6c4ebb

[llvmbot]

@llvm/issue-subscribers-backend-risc-v

Author: Yingwei Zheng (dtcxzyw)

Reduced test case: ``` #include "csmith.h" uint8_t a = 55; int32_t b; int32_t c[4]; uint32_t e[4]; void f() { int32_t *o = &c[1]; *o = 223; if (safe_mod_func_uint8_t_u_u(safe_sub_func_uint8_t_u_u(b, 1), a |= *o)) { e[0] = ++a; } } int main() { b = 0; f(); printf("%d\n", a); return 0; } ``` ``` > bin/clang -O0 --target=riscv64-linux-gnu test.c -I/usr/include/csmith -w > qemu-riscv64 -L /usr/riscv64-linux-gnu/ a.out 255 > bin/clang -O3 --target=riscv64-linux-gnu test.c -I/usr/include/csmith -w > qemu-riscv64 -L /usr/riscv64-linux-gnu/ a.out 224 ``` llvm version: d6c4ebb