[llvm] r227002 - [DAG] Fix wrong canonicalization performed on shuffle nodes.

[Andrea Di Biagio]

Author: adibiagio
Date: Sat Jan 24 05:54:29 2015
New Revision: 227002

URL: http://llvm.org/viewvc/llvm-project?rev=227002&view=rev
Log:
[DAG] Fix wrong canonicalization performed on shuffle nodes.

This fixes a regression introduced by r226816.
When replacing a splat shuffle node with a constant build_vector,
make sure that the new build_vector has a valid number of elements.

Thanks to Patrik Hagglund for reporting this problem and providing a
small reproducible.

Added:
    llvm/trunk/test/CodeGen/X86/selectiondag-crash.ll
Modified:
    llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

Modified: llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp?rev=227002&r1=227001&r2=227002&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp Sat Jan 24 05:54:29 2015
@@ -1538,13 +1538,15 @@ SDValue SelectionDAG::getVectorShuffle(E
       if (Splat && Splat.getOpcode() == ISD::UNDEF)
         return getUNDEF(VT);
 
+      bool SameNumElts =
+          V.getValueType().getVectorNumElements() == VT.getVectorNumElements();
+
       // We only have a splat which can skip shuffles if there is a splatted
       // value and no undef lanes rearranged by the shuffle.
       if (Splat && UndefElements.none()) {
         // Splat of <x, x, ..., x>, return <x, x, ..., x>, provided that the
         // number of elements match or the value splatted is a zero constant.
-        if (V.getValueType().getVectorNumElements() ==
-            VT.getVectorNumElements())
+        if (SameNumElts)
           return N1;
         if (auto *C = dyn_cast<ConstantSDNode>(Splat))
           if (C->isNullValue())
@@ -1553,15 +1555,15 @@ SDValue SelectionDAG::getVectorShuffle(E
 
       // If the shuffle itself creates a constant splat, build the vector
       // directly.
-      if (AllSame) {
+      if (AllSame && SameNumElts) {
          const SDValue &Splatted = BV->getOperand(MaskVec[0]);
          if (isa<ConstantSDNode>(Splatted) || isa<ConstantFPSDNode>(Splatted)) {
            SmallVector<SDValue, 8> Ops;
-           for (unsigned i = 0; i != NElts; ++i) {
+           for (unsigned i = 0; i != NElts; ++i)
              Ops.push_back(Splatted);
-           }
-           SDValue NewBV = getNode(ISD::BUILD_VECTOR, dl,
-             BV->getValueType(0), Ops);
+
+           SDValue NewBV =
+               getNode(ISD::BUILD_VECTOR, dl, BV->getValueType(0), Ops);
 
            // We may have jumped through bitcasts, so the type of the
            // BUILD_VECTOR may not match the type of the shuffle.

Added: llvm/trunk/test/CodeGen/X86/selectiondag-crash.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/selectiondag-crash.ll?rev=227002&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/X86/selectiondag-crash.ll (added)
+++ llvm/trunk/test/CodeGen/X86/selectiondag-crash.ll Sat Jan 24 05:54:29 2015
@@ -0,0 +1,15 @@
+; RUN: llc -mtriple=x86_64-unknown-unknown -mcpu=corei7 < %s
+
+; Check that llc doesn't crash in the attempt to fold a shuffle with
+; a splat mask into a constant build_vector.
+
+define <8 x i8> @autogen_SD26299(i8) {
+BB:
+  %Shuff = shufflevector <8 x i32> <i32 -1, i32 -1, i32 -1, i32 -1, i32 -1, i32 -1, i32 -1, i32 -1>, <8 x i32> zeroinitializer, <8 x i32> <i32 2, i32 undef, i32 6, i32 8, i32 undef, i32 12, i32 14, i32 0>
+  %Shuff14 = shufflevector <8 x i32> %Shuff, <8 x i32> %Shuff, <8 x i32> <i32 7, i32 9, i32 11, i32 undef, i32 undef, i32 1, i32 3, i32 5>
+  %Shuff35 = shufflevector <8 x i32> %Shuff14, <8 x i32> %Shuff, <8 x i32> <i32 undef, i32 1, i32 3, i32 5, i32 7, i32 9, i32 11, i32 13>
+  %I42 = insertelement <8 x i32> %Shuff35, i32 88608, i32 0
+  %Shuff48 = shufflevector <8 x i32> %Shuff35, <8 x i32> %I42, <8 x i32> <i32 4, i32 6, i32 8, i32 10, i32 12, i32 14, i32 0, i32 2>
+  %Tr59 = trunc <8 x i32> %Shuff48 to <8 x i8>
+  ret <8 x i8> %Tr59
+}