[PATCH] D88578: [InstCombine] recognizeBSwapOrBitReverseIdiom - support for 'partial' bswap patterns (PR47191)

[Sanjay Patel via Phabricator via llvm-commits]

spatel added inline comments.


================
Comment at: llvm/test/Transforms/InstCombine/bswap.ll:382
+; CHECK-NEXT:    [[TMP6:%.*]] = or i64 [[TMP3]], [[TMP5]]
+; CHECK-NEXT:    ret i64 [[TMP6]]
 ;
----------------
RKSimon wrote:
> We would have reduced this to bswap+mask but InstCombinerImpl::matchBSwap is too harsh at filtering out or(A,B) patterns where A and B have different opcodes.
Add test(s) that already have a partial bswap, so we can see the most basic transform enabled by this patch?

Something like this:

```
define i32 @partial_bswap(i32 %x) {
  %x3 = shl i32 %x, 24
  %a2 = shl i32 %x, 8
  %x2 = and i32 %a2, 16711680
  %x32 = or i32 %x3, %x2
  %t1 = and i32 %x, -65536
  %t2 = call i32 @llvm.bswap.i32(i32 %t1)
  %r = or i32 %x32, %t2
  ret i32 %r
}

```


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D88578/new/

https://reviews.llvm.org/D88578