[llvm] [X86] LowerShift - track the number and location of constant shift elements. (PR #120270)

[Phoebe Wang via llvm-commits]

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@@ -30057,6 +30057,23 @@ static SDValue LowerShift(SDValue Op, const X86Subtarget &Subtarget,
     return DAG.getVectorShuffle(VT, dl, R0, R1, {0, 3});
   }
 
+  // Build a map of inrange constant amounts with element mask where they occur.
+  std::map<unsigned, APInt> UniqueCstAmt;
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phoebewang wrote:

Is bettter to use `DenseMap`?

https://github.com/llvm/llvm-project/pull/120270