[PATCH] D113371: [X86] combinePMULH - recognise 'cheap' trunctions via PACKS/PACKUS as well as SEXT/ZEXT

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri added inline comments.


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Comment at: llvm/lib/Target/X86/X86ISelLowering.cpp:48325-48327
+    unsigned NumBits = V.getScalarValueSizeInBits();
+    unsigned NumSignBits = DAG.ComputeNumSignBits(V);
+    return (NumSignBits + 16) > NumBits;
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Can you mirror rG61225c081858efe55dfc7051b338c797fab07cff and introduce `DAG.ComputeMinSignedBits()`?
Then this becomes an obvious `return DAG.ComputeMinSignedBits() <= 16;`


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Comment at: llvm/lib/Target/X86/X86ISelLowering.cpp:48331
+    KnownBits Known = DAG.computeKnownBits(V);
+    return (Known.countMinLeadingZeros() + 16) >= Known.getBitWidth();
+  };
----------------
`return Known.countMaxActiveBits() <= 16;`


Repository:
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  https://reviews.llvm.org/D113371/new/

https://reviews.llvm.org/D113371