[llvm] [LLVM][AArch64] Improve big endian code generation for SVE BITCASTs. (PR #104769)

[Paul Walker via llvm-commits]

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@@ -28877,7 +28885,20 @@ SDValue AArch64TargetLowering::getSVESafeBitCast(EVT VT, SDValue Op,
   if (InVT != PackedInVT)
     Op = DAG.getNode(AArch64ISD::REINTERPRET_CAST, DL, PackedInVT, Op);
 
-  Op = DAG.getNode(ISD::BITCAST, DL, PackedVT, Op);
+  if (Subtarget->isLittleEndian() ||
+      PackedVT.getScalarSizeInBits() == PackedInVT.getScalarSizeInBits())
+    Op = DAG.getNode(ISD::BITCAST, DL, PackedVT, Op);
+  else {
+    EVT PackedVTAsInt = PackedVT.changeTypeToInteger();
+    EVT PackedInVTAsInt = PackedInVT.changeTypeToInteger();
+
+    // Simulate the effect of casting through memory.
+    Op = DAG.getNode(ISD::BITCAST, DL, PackedInVTAsInt, Op);
+    Op = DAG.getNode(ISD::BSWAP, DL, PackedInVTAsInt, Op);
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paulwalker-arm wrote:

For context https://github.com/llvm/llvm-project/pull/104820/commits/245d3c6491fdcacd29dbaf632741072e48865803 contains the fixes I'm referring to above.  You'll see this still affects some of the big endian bitcast tests but it's more contained (albeit I've not verified the changes are all correct yet). That PR is still a work in progress.

https://github.com/llvm/llvm-project/pull/104769