[PATCH] D88834: [InstCombine] matchRotate - add support for matching general funnel shifts with constant shift amounts (PR46896)

[Sanjay Patel via Phabricator via llvm-commits]

spatel added inline comments.


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Comment at: llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp:2080
 
   // First, find an or'd pair of opposite shifts with the same shifted operand:
+  // or (lshr ShVal0, ShAmt0), (shl ShVal1, ShAmt1)
----------------
Remove "with the same shifted operand".


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Comment at: llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp:2107-2108
 
+    // For non-constant cases, the following patterns currently only support
+    // rotation patterns.
+    if (ShVal0 != ShVal1)
----------------
Sorry - it's still not clear to me *why* we have this clause. Are we regressing something without this restriction, or is the expanded IR pattern with a variable shift amount different between general funnel vs. rotate?


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  https://reviews.llvm.org/D88834/new/

https://reviews.llvm.org/D88834