https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115749
--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
For the original testcase, the imul vs shift can be reduced down to just:
```
unsigned long func(unsigned long x)
{
return x * 240;
}
```
GCC produces:
```
movq %rdi, %rax
salq $4, %rax
subq %rdi, %rax
salq $4, %rax
```
vs:
```
imulq $240, %rdi, %rax
```
-mtune=skylake produces the imul.
The mulx issue can be reduced down to just:
```
unsigned long func(unsigned long x)
{
__uint128_t t = x;
return (t * 123)>>64;
}
__uint128_t func1(unsigned long x, unsigned long y)
{
__uint128_t t = x;
return (t * 123);
}
```
It only happens with constants it seems.
