Noah Goldstein 9ef829097b [InstCombine] Fix buggy transform in foldNestedSelects; PR 71330
The bug is that `IsAndVariant` is used to assume which arm in the
select the output `SelInner` should be placed but match the inner
select condition with `m_c_LogicalOp`. With fully simplified ops, this
works fine, but its possible if the select condition is not
simplified, for it match both `LogicalAnd` and `LogicalOr` i.e `select
true, true, false`.

In PR71330 for example, the issue occurs in the following IR:
```
define i32 @bad() {
  %..i.i = select i1 false, i32 0, i32 3
  %brmerge = select i1 true, i1 true, i1 false
  %not.cmp.i.i.not = xor i1 true, true
  %.mux = zext i1 %not.cmp.i.i.not to i32
  %retval.0.i.i = select i1 %brmerge, i32 %.mux, i32 %..i.i
  ret i32 %retval.0.i.i
}
```

When simplifying:
```
%retval.0.i.i = select i1 %brmerge, i32 %.mux, i32 %..i.i
```

We end up matching `%brmerge` as `LogicalAnd` for `IsAndVariant`, but
the inner select (`%..i.i`) condition which is `false` with
`LogicalOr`.

Closes #71489
2023-11-09 16:36:49 -06:00
..
2022-08-24 22:41:38 +00:00

This directory contains test cases for the instcombine transformation.  The
dated tests are actual bug tests, whereas the named tests are used to test
for features that the this pass should be capable of performing.