[PATCH] D48491: [X86] Select BEXTR when there is only BMI1.

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri added a comment.

In https://reviews.llvm.org/D48491#1141822, @craig.topper wrote:

> Matching multiple nodes in isel patterns without one use checks and then emitting multiple instructions for the pattern seems like dangerous territory. Is there more canonicalizing we should be doing in DAG combines to get these sequences into a form we can handle in isel?




  ; Patterns:
  ;   a) x &  (1 << nbits) - 1
  ;   b) x & ~(-1 << nbits)
  ;   c) x &  (-1 >> (32 - y))
  ;   d) x << (32 - y) >> (32 - y)

We do canonicalize `a` -> `b` and `d` -> `c` in instcombine.
We could do the same in dagcombine.


Repository:
  rL LLVM

https://reviews.llvm.org/D48491