[PATCH] D45173: [InstCombine] Recognize idioms for ctpop and ctlz

[Craig Topper via Phabricator via llvm-commits]

craig.topper added inline comments.


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Comment at: lib/Transforms/AggressiveInstCombine/BitCountCombine.cpp:52
+Value *BitCountCombine::matchCtpopW(Instruction &In, unsigned BW) {
+  auto matchStep = [] (Value *V, unsigned S, APInt M, bool ShiftAlone)
+        -> Value* {
----------------
Should take APInt M by const reference if possible to avoid a costly copy if its larger than 64 bits.


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Comment at: lib/Transforms/AggressiveInstCombine/BitCountCombine.cpp:73
+      }
+      if (!APInt::isSameValue(M, *P))
+        return nullptr;
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APInt::isSameValue is most useful when the APInts have different widths. Is that the case here? If not we should just use operator==


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Comment at: lib/Transforms/AggressiveInstCombine/BitCountCombine.cpp:194
+
+  IntegerType *Ty = cast<IntegerType>(V->getType());
+  KnownBits K(Ty->getBitWidth());
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What if the ctpop returns a vector type?


Repository:
  rL LLVM

https://reviews.llvm.org/D45173