[PATCH] D98587: [X86] Optimize vXi8 MULHS on targets where we can't sign_extend to the next register size.

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon added inline comments.


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Comment at: llvm/lib/Target/X86/X86ISelLowering.cpp:27492
+  // We'll take different approaches for signed and unsigned.
+  // For unsigned we'll use punpcklbw/punpckhbw to put zero extend the bytes
+  // and use pmullw to calculate the full 16-bit product.
----------------
"put zero extend the bytes" ?


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Comment at: llvm/lib/Target/X86/X86ISelLowering.cpp:27504
+    ALo = DAG.getBitcast(
+        ExVT, getUnpackl(DAG, dl, VT, DAG.getConstant(0, dl, VT), A));
+    AHi = DAG.getBitcast(
----------------
Pull out repeated DAG.getConstant(0, dl, VT) calls


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Comment at: llvm/lib/Target/X86/X86ISelLowering.cpp:27546
+    BHi = DAG.getBitcast(
+        ExVT, getUnpackh(DAG, dl, VT, DAG.getConstant(0, dl, VT), B));
   } else {
----------------
More repeated DAG.getConstant(0, dl, VT) calls?


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D98587/new/

https://reviews.llvm.org/D98587