[llvm] r180871 - Optimize away nop CONCAT_VECTOR nodes.

[Kuperstein, Michael M]

Hi Nadav,

This breaks a case where a concat_vector has a single non-undef source, but concatenates it with an undef in order to extend the vector. I'm attaching a test-case and a proposed patch. 
Only ran x86 tests, not ARM, can you check this doesn't break the original issue? If it looks ok, I'll add the test to the patch and commit.

Thanks,
   Michael

-----Original Message-----
From: llvm-commits-bounces at cs.uiuc.edu [mailto:llvm-commits-bounces at cs.uiuc.edu] On Behalf Of Nadav Rotem
Sent: Wednesday, May 01, 2013 22:19
To: llvm-commits at cs.uiuc.edu
Subject: [llvm] r180871 - Optimize away nop CONCAT_VECTOR nodes.

Author: nadav
Date: Wed May  1 14:18:51 2013
New Revision: 180871

URL: http://llvm.org/viewvc/llvm-project?rev=180871&view=rev
Log:
Optimize away nop CONCAT_VECTOR nodes.

Optimize CONCAT_VECTOR nodes that merge EXTRACT_SUBVECTOR values that extract from the same vector.

rdar://13402653
PR15866


Added:
    llvm/trunk/test/CodeGen/ARM/nop_concat_vectors.ll
Modified:
    llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

Modified: llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp?rev=180871&r1=180870&r2=180871&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp Wed May  1 
+++ 14:18:51 2013
@@ -9122,6 +9122,45 @@ SDValue DAGCombiner::visitCONCAT_VECTORS
   if (ISD::allOperandsUndef(N))
     return DAG.getUNDEF(N->getValueType(0));
 
+  // Type legalization of vectors and DAG canonicalization of 
+ SHUFFLE_VECTOR  // nodes often generate nop CONCAT_VECTOR nodes.
+  // Scan the CONCAT_VECTOR operands and look for a CONCAT operations 
+ that  // place the incoming vectors at the exact same location.
+  SDValue SingleSource = SDValue();
+  unsigned PartNumElem = 
+ N->getOperand(0).getValueType().getVectorNumElements();
+
+  for (unsigned i = 0, e = N->getNumOperands(); i != e; ++i) {
+    SDValue Op = N->getOperand(i);
+
+    if (Op.getOpcode() == ISD::UNDEF)
+      continue;
+
+    // Check if this is the identity extract:
+    if (Op.getOpcode() != ISD::EXTRACT_SUBVECTOR)
+      return SDValue();
+
+    // Find the single incoming vector for the extract_subvector.
+    if (SingleSource.getNode()) {
+      if (Op.getOperand(0) != SingleSource)
+        return SDValue();
+    } else {
+      SingleSource = Op.getOperand(0);
+    }
+
+    unsigned IdentityIndex = i * PartNumElem;
+    ConstantSDNode *CS = dyn_cast<ConstantSDNode>(Op.getOperand(1));
+    // The extract index must be constant.
+    if (!CS)
+      return SDValue();
+    
+    // Check that we are reading from the identity index.
+    if (CS->getZExtValue() != IdentityIndex)
+      return SDValue();
+  }
+
+  if (SingleSource.getNode())
+    return SingleSource;
+  
   return SDValue();
 }
 

Added: llvm/trunk/test/CodeGen/ARM/nop_concat_vectors.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/ARM/nop_concat_vectors.ll?rev=180871&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/ARM/nop_concat_vectors.ll (added)
+++ llvm/trunk/test/CodeGen/ARM/nop_concat_vectors.ll Wed May  1 
+++ 14:18:51 2013
@@ -0,0 +1,13 @@
+; RUN: llc < %s -mtriple=armv7-apple-darwin | FileCheck %s
+
+;CHECK: _foo
+;CHECK-NOT: vld1.32
+;CHECK-NOT: vst1.32
+;CHECK: bx
+define void @foo(<16 x i8>* %J) {
+  %A = load <16 x i8>* %J
+  %T1 = shufflevector <16 x i8> %A, <16 x i8> undef, <8 x i32> <i32 8, 
+i32 9, i32 10, i32 11, i32 12, i32 13, i32 14, i32 15>
+  %T2 = shufflevector <8 x i8>  %T1, <8 x i8> undef, <16 x i32> <i32 
+undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 
+undef, i32 undef, i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 
+7>
+  store <16 x i8> %T2, <16 x i8>* %J
+  ret void
+}


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