[llvm] c6c5aad - [X86] truncateVectorWithPACK - avoid concat_vectors(extract_subvector(pack()),extract_subvector(pack())) for sub-128 bit vectors

[Simon Pilgrim via llvm-commits]

Author: Simon Pilgrim
Date: 2023-07-21T19:10:17+01:00
New Revision: c6c5aad6a24311e855b6ab7054b861a0a066e08c

URL: https://github.com/llvm/llvm-project/commit/c6c5aad6a24311e855b6ab7054b861a0a066e08c
DIFF: https://github.com/llvm/llvm-project/commit/c6c5aad6a24311e855b6ab7054b861a0a066e08c.diff

LOG: [X86] truncateVectorWithPACK - avoid concat_vectors(extract_subvector(pack()),extract_subvector(pack())) for sub-128 bit vectors

As we start using this after type legalization, we must avoid creating concat_vectors nodes so late.

Added: 
    

Modified: 
    llvm/lib/Target/X86/X86ISelLowering.cpp

Removed: 
    


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diff  --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 7c322faa6a208d..8ff3d86b81317e 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -22890,11 +22890,19 @@ static SDValue truncateVectorWithPACK(unsigned Opcode, EVT DstVT, SDValue In,
 
   // Recursively pack lower/upper subvectors, concat result and pack again.
   assert(SrcSizeInBits >= 256 && "Expected 256-bit vector or greater");
-  EVT PackedVT = EVT::getVectorVT(Ctx, PackedSVT, NumElems / 2);
-  Lo = truncateVectorWithPACK(Opcode, PackedVT, Lo, DL, DAG, Subtarget);
-  Hi = truncateVectorWithPACK(Opcode, PackedVT, Hi, DL, DAG, Subtarget);
 
-  PackedVT = EVT::getVectorVT(Ctx, PackedSVT, NumElems);
+  EVT PackedVT = EVT::getVectorVT(Ctx, PackedSVT, NumElems);
+  if (PackedVT.is128BitVector()) {
+    // Avoid CONCAT_VECTORS on sub-128bit nodes as these can fail after
+    // type legalization.
+    SDValue Res =
+        truncateVectorWithPACK(Opcode, PackedVT, In, DL, DAG, Subtarget);
+    return truncateVectorWithPACK(Opcode, DstVT, Res, DL, DAG, Subtarget);
+  }
+
+  EVT HalfPackedVT = EVT::getVectorVT(Ctx, PackedSVT, NumElems / 2);
+  Lo = truncateVectorWithPACK(Opcode, HalfPackedVT, Lo, DL, DAG, Subtarget);
+  Hi = truncateVectorWithPACK(Opcode, HalfPackedVT, Hi, DL, DAG, Subtarget);
   SDValue Res = DAG.getNode(ISD::CONCAT_VECTORS, DL, PackedVT, Lo, Hi);
   return truncateVectorWithPACK(Opcode, DstVT, Res, DL, DAG, Subtarget);
 }