[PATCH] D149699: [InstCombine] Improve bswap optimization

[Noah Goldstein via Phabricator via llvm-commits]

goldstein.w.n added inline comments.


================
Comment at: llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp:1296
+    }
+  }
+  return nullptr;
----------------
In that case that both X and Y match the intrinsic, we should still do the optimization even if X/Y have multi-use.
I.e
```
declare i16 @llvm.bswap.i16(i16)
declare void @use.i16(i16)
define i16 @bs_and_lhs_bs16(i16 %x, i16 %y) {
  %bx = tail call i16 @llvm.bswap.i16(i16 %x)
  %by = tail call i16 @llvm.bswap.i16(i16 %y)
  %r = and i16 %bx, %by
  %br = tail call i16 @llvm.bswap.i16(i16 %r)

  call void @use.i16(i16 %bx)
  call void @use.i16(i16 %by)    
  ret i16 %br
}
```

Should become:
```
declare i16 @llvm.bswap.i16(i16)
declare void @use.i16(i16)
define i16 @bs_and_lhs_bs16(i16 %x, i16 %y) {
  %bx = tail call i16 @llvm.bswap.i16(i16 %x)
  %by = tail call i16 @llvm.bswap.i16(i16 %y)
  %r = and i16 %x, %y
  call void @use.i16(i16 %bx)
  call void @use.i16(i16 %by)    
  ret i16 %r
}
```

I think an initiali if statement that check for that case would work.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D149699/new/

https://reviews.llvm.org/D149699