Alex MacLean 8361d9065e [InstCombine] disable select folding resulting in extra instructions (#97184) ...

Disable conversion of a `(select (icmp))` when it would result in more
instructions `(xor (lshr (and)))`. This transformation produces more
instructions and can interfere with other more profitable folds for
`select`. For example before this change the following folding would
occur:
```llvm
  %1 = icmp slt i32 %X, 0
  %2 = select i1 %1, i64 0, i64 8
```
to 
```llvm
  %1 = lshr i32 %X, 28
  %2 = and i32 %1, 8
  %3 = xor i32 %2, 8
  %4 = zext nneg i32 %3 to i64
```

2024-07-01 08:10:56 -07:00

159 KiB

Raw Blame History

View Raw