SelectionDAG: Teach the legalizer to split SETCC if VSELECT needs splitting too.

The Type Legalizer recognizes that VSELECT needs to be split, because the type
is to wide for the given target. The same does not always apply to SETCC,
because less space is required to encode the result of a comparison. As a result
VSELECT is split and SETCC is unrolled into scalar comparisons.

This commit fixes the issue by checking for VSELECT-SETCC patterns in the DAG
Combiner. If a matching pattern is found, then the result mask of SETCC is
promoted to the expected vector mask type for the given target. This mask has
usually the same size as the VSELECT return type (except for Intel KNL). Now the
type legalizer will split both VSELECT and SETCC.

This allows the following X86 DAG Combine code to sucessfully detect the MIN/MAX
pattern. This fixes PR16695, PR17002, and <rdar://problem/14594431>.

Reviewed by Nadav

llvm-svn: 193676

4 files changed, 87 insertions, 9 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index de0f6ce26d9..8237ef3779b 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -4346,6 +4346,28 @@ SDValue DAGCombiner::visitVSELECT(SDNode *N) {
     }
   }
 
+  // Treat SETCC as a vector mask and promote the result type based on the
+  // targets expected SETCC result type. This will ensure that SETCC and VSELECT
+  // are both split by the type legalizer. This is done to prevent the type
+  // legalizer from unrolling SETCC into scalar comparions.
+  EVT SelectVT = N->getValueType(0);
+  EVT MaskVT = getSetCCResultType(SelectVT);
+  if (N0.getOpcode() == ISD::SETCC && N0.getValueType() != MaskVT) {
+    SDLoc MaskDL(N0);
+
+    // Extend the mask to the desired value type.
+    ISD::NodeType ExtendCode =
+      TargetLowering::getExtendForContent(TLI.getBooleanContents(true));
+    SDValue Mask = DAG.getNode(ExtendCode, MaskDL, MaskVT, N0);
+
+    AddToWorkList(Mask.getNode());
+
+    SDValue LHS = N->getOperand(1);
+    SDValue RHS = N->getOperand(2);
+
+    return DAG.getNode(ISD::VSELECT, DL, SelectVT, Mask, LHS, RHS);
+  }
+
   return SDValue();
 }
 
diff --git a/llvm/lib/CodeGen/SelectionDAG/LegalizeTypesGeneric.cpp b/llvm/lib/CodeGen/SelectionDAG/LegalizeTypesGeneric.cpp
index 7b1d14dad0c..f1b06fcd983 100644
--- a/llvm/lib/CodeGen/SelectionDAG/LegalizeTypesGeneric.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/LegalizeTypesGeneric.cpp
@@ -492,14 +492,19 @@ void DAGTypeLegalizer::SplitRes_SELECT(SDNode *N, SDValue &Lo,
   SDValue Cond = N->getOperand(0);
   CL = CH = Cond;
   if (Cond.getValueType().isVector()) {
-    assert(Cond.getValueType().getVectorElementType() == MVT::i1 &&
-           "Condition legalized before result?");
-    unsigned NumElements = Cond.getValueType().getVectorNumElements();
-    EVT VCondTy = EVT::getVectorVT(*DAG.getContext(), MVT::i1, NumElements / 2);
-    CL = DAG.getNode(ISD::EXTRACT_SUBVECTOR, dl, VCondTy, Cond,
-                     DAG.getConstant(0, TLI.getVectorIdxTy()));
-    CH = DAG.getNode(ISD::EXTRACT_SUBVECTOR, dl, VCondTy, Cond,
-                     DAG.getConstant(NumElements / 2, TLI.getVectorIdxTy()));
+    if (Cond.getOpcode() == ISD::SETCC) {
+      assert(Cond.getValueType() == getSetCCResultType(N->getValueType(0)) &&
+             "Condition has not been prepared for split!");
+      GetSplitVector(Cond, CL, CH);
+    } else {
+      EVT ETy = Cond.getValueType().getVectorElementType();
+      unsigned NumElements = Cond.getValueType().getVectorNumElements();
+      EVT VCondTy = EVT::getVectorVT(*DAG.getContext(), ETy, NumElements / 2);
+      CL = DAG.getNode(ISD::EXTRACT_SUBVECTOR, dl, VCondTy, Cond,
+                       DAG.getConstant(0, TLI.getVectorIdxTy()));
+      CH = DAG.getNode(ISD::EXTRACT_SUBVECTOR, dl, VCondTy, Cond,
+                       DAG.getConstant(NumElements / 2, TLI.getVectorIdxTy()));
+    }
   }
 
   Lo = DAG.getNode(N->getOpcode(), dl, LL.getValueType(), CL, LL, RL);
diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 5dbef0f6fc3..18064fc6159 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -1546,7 +1546,16 @@ void X86TargetLowering::resetOperationActions() {
 }
 
 EVT X86TargetLowering::getSetCCResultType(LLVMContext &, EVT VT) const {
-  if (!VT.isVector()) return MVT::i8;
+  if (!VT.isVector())
+    return MVT::i8;
+
+  const TargetMachine &TM = getTargetMachine();
+  if (!TM.Options.UseSoftFloat && Subtarget->hasAVX512())
+    switch(VT.getVectorNumElements()) {
+    case  8: return MVT::v8i1;
+    case 16: return MVT::v16i1;
+    }
+
   return VT.changeVectorElementTypeToInteger();
 }
 
diff --git a/llvm/test/CodeGen/X86/vec_split.ll b/llvm/test/CodeGen/X86/vec_split.ll
new file mode 100644
index 00000000000..f9e7c20ba4e
--- /dev/null
+++ b/llvm/test/CodeGen/X86/vec_split.ll
@@ -0,0 +1,42 @@
+; RUN: llc -march=x86-64 -mcpu=corei7 < %s | FileCheck %s -check-prefix=SSE4
+; RUN: llc -march=x86-64 -mcpu=corei7-avx < %s | FileCheck %s -check-prefix=AVX1
+; RUN: llc -march=x86-64 -mcpu=core-avx2 < %s | FileCheck %s -check-prefix=AVX2
+
+define <16 x i16> @split16(<16 x i16> %a, <16 x i16> %b, <16 x i8> %__mask) {
+; SSE4-LABEL: split16:
+; SSE4: pminuw
+; SSE4: pminuw
+; SSE4: ret
+; AVX1-LABEL: split16:
+; AVX1: vpminuw
+; AVX1: vpminuw
+; AVX1: ret
+; AVX2-LABEL: split16:
+; AVX2: vpminuw
+; AVX2: ret
+  %1 = icmp ult <16 x i16> %a, %b
+  %2 = select <16 x i1> %1, <16 x i16> %a, <16 x i16> %b
+  ret <16 x i16> %2
+}
+
+define <32 x i16> @split32(<32 x i16> %a, <32 x i16> %b, <32 x i8> %__mask) {
+; SSE4-LABEL: split32:
+; SSE4: pminuw
+; SSE4: pminuw
+; SSE4: pminuw
+; SSE4: pminuw
+; SSE4: ret
+; AVX1-LABEL: split32:
+; AVX1: vpminuw
+; AVX1: vpminuw
+; AVX1: vpminuw
+; AVX1: vpminuw
+; AVX1: ret
+; AVX2-LABEL: split32:
+; AVX2: vpminuw
+; AVX2: vpminuw
+; AVX2: ret
+  %1 = icmp ult <32 x i16> %a, %b
+  %2 = select <32 x i1> %1, <32 x i16> %a, <32 x i16> %b
+  ret <32 x i16> %2
+}