On Fri, 2024-07-19 at 15:46 -0700, Andrii Nakryiko wrote: [...] > > + /* Here we would like to handle a special case after sign extending load, > > + * when upper bits for a 64-bit range are all 1s or all 0s. > > + * > > + * Upper bits are all 1s when register is in a range: > > + * [0xffff_ffff_0000_0000, 0xffff_ffff_ffff_ffff] > > + * Upper bits are all 0s when register is in a range: > > + * [0x0000_0000_0000_0000, 0x0000_0000_ffff_ffff] > > + * Together this forms are continuous range: > > + * [0xffff_ffff_0000_0000, 0x0000_0000_ffff_ffff] > > + * > > + * Now, suppose that register range is in fact tighter: > > + * [0xffff_ffff_8000_0000, 0x0000_0000_ffff_ffff] (R) > > + * Also suppose that it's 32-bit range is positive, > > + * meaning that lower 32-bits of the full 64-bit register > > + * are in the range: > > + * [0x0000_0000, 0x7fff_ffff] (W) > > + * > > + * If this happens, then any value in a range: > > + * [0xffff_ffff_0000_0000, 0xffff_ffff_7fff_ffff] > > + * is smaller than a lowest bound of the range (R): > > + * 0xffff_ffff_8000_0000 > > + * which means that upper bits of the full 64-bit register > > + * can't be all 1s, when lower bits are in range (W). > > + * > > + * Note that: > > + * - 0xffff_ffff_8000_0000 == (s64)S32_MIN > > + * - 0x0000_0000_ffff_ffff == (s64)S32_MAX > > ?? S32_MAX = 0x7fffffff, so should the right part be U32_MAX or the > left part should be 0x0000_0000_7fff_ffff ? Oops, that's on me, yes it should be 0x0000_0000_7fff_ffff here. [...]
