Fix an infinite loop bug in DAG Combine about keeping transfering between ANY_EXTEND and SIGN_EXTEND.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206873 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 38 insertions, 10 deletions

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index cdf1aedd97..a52dacf521 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -5479,7 +5479,10 @@ SDValue DAGCombiner::visitANY_EXTEND(SDNode *N) {
   }
 
   if (N0.getOpcode() == ISD::SETCC) {
-    // aext(setcc) -> sext_in_reg(vsetcc) for vectors.
+    // For vectors:
+    // aext(setcc) -> vsetcc
+    // aext(setcc) -> truncate(vsetcc)
+    // aext(setcc) -> aext(vsetcc)
     // Only do this before legalize for now.
     if (VT.isVector() && !LegalOperations) {
       EVT N0VT = N0.getOperand(0).getValueType();
@@ -5494,19 +5497,14 @@ SDValue DAGCombiner::visitANY_EXTEND(SDNode *N) {
                              cast<CondCodeSDNode>(N0.getOperand(2))->get());
       // If the desired elements are smaller or larger than the source
       // elements we can use a matching integer vector type and then
-      // truncate/sign extend
+      // truncate/any extend
       else {
-        EVT MatchingElementType =
-          EVT::getIntegerVT(*DAG.getContext(),
-                            N0VT.getScalarType().getSizeInBits());
-        EVT MatchingVectorType =
-          EVT::getVectorVT(*DAG.getContext(), MatchingElementType,
-                           N0VT.getVectorNumElements());
+        EVT MatchingVectorType = N0VT.changeVectorElementTypeToInteger();
         SDValue VsetCC =
           DAG.getSetCC(SDLoc(N), MatchingVectorType, N0.getOperand(0),
                         N0.getOperand(1),
                         cast<CondCodeSDNode>(N0.getOperand(2))->get());
-        return DAG.getSExtOrTrunc(VsetCC, SDLoc(N), VT);
+        return DAG.getAnyExtOrTrunc(VsetCC, SDLoc(N), VT);
       }
     }
 
diff --git a/test/CodeGen/ARM64/2014-04-16-AnInfiniteLoopInDAGCombine.ll b/test/CodeGen/ARM64/2014-04-16-AnInfiniteLoopInDAGCombine.ll
new file mode 100644
index 0000000000..a73b707180
--- /dev/null
+++ b/test/CodeGen/ARM64/2014-04-16-AnInfiniteLoopInDAGCombine.ll
@@ -0,0 +1,23 @@
+; RUN: llc < %s -march=arm64
+
+; This test case tests an infinite loop bug in DAG combiner.
+; It just tries to do the following replacing endlessly:
+; (1)  Replacing.3 0x2c509f0: v4i32 = any_extend 0x2c4cd08 [ORD=4]
+;      With: 0x2c4d128: v4i32 = sign_extend 0x2c4cd08 [ORD=4]
+;
+; (2)  Replacing.2 0x2c4d128: v4i32 = sign_extend 0x2c4cd08 [ORD=4]
+;      With: 0x2c509f0: v4i32 = any_extend 0x2c4cd08 [ORD=4]
+; As we think the (2) optimization from SIGN_EXTEND to ANY_EXTEND is
+; an optimization to replace unused bits with undefined bits, we remove
+; the (1) optimization (It doesn't make sense to replace undefined bits
+; with signed bits).
+
+define <4 x i32> @infiniteLoop(<4 x i32> %in0, <4 x i16> %in1) {
+entry:
+  %cmp.i = icmp sge <4 x i16> %in1, <i16 32767, i16 32767, i16 -1, i16 -32768>
+  %sext.i = sext <4 x i1> %cmp.i to <4 x i32>
+  %mul.i = mul <4 x i32> %in0, %sext.i
+  %sext = shl <4 x i32> %mul.i, <i32 16, i32 16, i32 16, i32 16>
+  %vmovl.i.i = ashr <4 x i32> %sext, <i32 16, i32 16, i32 16, i32 16>
+  ret <4 x i32> %vmovl.i.i
+}
\ No newline at end of file
diff --git a/test/CodeGen/ARM64/vselect.ll b/test/CodeGen/ARM64/vselect.ll
index 07274a0501..aa8e81eb70 100644
--- a/test/CodeGen/ARM64/vselect.ll
+++ b/test/CodeGen/ARM64/vselect.ll
@@ -2,7 +2,14 @@
 
 ;CHECK: @func63
 ;CHECK: cmeq.4h v0, v0, v1
-;CHECK: sshll.4s  v0, v0, #0
+
+;FIXME: currently, it will generate 3 instructions:
+; ushll.4s	v0, v0, #0
+; shl.4s	v0, v0, #31
+; sshr.4s	v0, v0, #31
+;But these instrucitons can be optimized into 1 instruction:
+; sshll.4s  v0, v0, #0
+
 ;CHECK: bsl.16b v0, v2, v3
 ;CHECK: str  q0, [x0]
 ;CHECK: ret