[llvm] [Codegen][LegalizeIntegerTypes] Improve shift through stack (PR #96151)

[Matt Arsenault via llvm-commits]

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@@ -4530,14 +4530,25 @@ void DAGTypeLegalizer::ExpandIntRes_ShiftThroughStack(SDNode *N, SDValue &Lo,
   SDValue ShAmt = N->getOperand(1);
   EVT ShAmtVT = ShAmt.getValueType();
 
-  // This legalization is optimal when the shift is by a multiple of byte width,
-  //   %x * 8 <-> %x << 3   so 3 low bits should be be known zero.
-  bool ShiftByByteMultiple =
-      DAG.computeKnownBits(ShAmt).countMinTrailingZeros() >= 3;
+  EVT LoadStoreVT = VT;
+  do {
+      LoadStoreVT = TLI.getTypeToTransformTo(*DAG.getContext(), LoadStoreVT);
+  }while (!TLI.isTypeLegal(LoadStoreVT));
+
+  const Align LoadStoreAlign = [&]() -> Align {
+      if (TLI.allowsMisalignedMemoryAccesses(LoadStoreVT))
+          return Align(1);
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arsenm wrote:

Don't understand this. Just because it's allowed doesn't mean it's a good idea to use Align 1

https://github.com/llvm/llvm-project/pull/96151