1 files changed, 29 insertions, 0 deletions
diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index e92a099753b..37026ce0f12 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -24757,6 +24757,8 @@ static SDValue PerformLOADCombine(SDNode *N, SelectionDAG &DAG,
   LoadSDNode *Ld = cast<LoadSDNode>(N);
   EVT RegVT = Ld->getValueType(0);
   EVT MemVT = Ld->getMemoryVT();
+  SDValue Ptr   = Ld->getBasePtr();
+  SDValue Chain = Ld->getChain();
   SDLoc dl(Ld);
   const TargetLowering &TLI = DAG.getTargetLoweringInfo();
 
@@ -24795,6 +24797,33 @@ static SDValue PerformLOADCombine(SDNode *N, SelectionDAG &DAG,
     return DCI.CombineTo(N, NewVec, TF, true);
   }
 
+  // Conversion from x86mmx/i64 to v2i64 types is often done via stack
+  // store/load. Under certain conditions we can bypass the memory access and
+  // combine this load to use a scalar_to_vector instead. This leads to
+  // a reduction in the stack use, redundant emission of shuffles and create
+  // isel matching candidates for movq2dq instructions.
+  if (RegVT == MVT::v2i64 && Subtarget->hasSSE2() && Ext == ISD::EXTLOAD &&
+      !Ld->isVolatile() && ISD::isNON_TRUNCStore(Chain.getNode())) {
+
+    // If this load is directly stored, get the original source value.
+    StoreSDNode *PrevST = cast<StoreSDNode>(Chain);
+    EVT SrcTy = PrevST->getValue().getValueType();
+    if (PrevST->getBasePtr() != Ptr ||
+        !(SrcTy == MVT::i64 || SrcTy == MVT::x86mmx))
+      return SDValue();
+    SDValue SrcVal = Chain.getOperand(1);
+
+    // On 32bit systems, we can't save 64bit integers, use f64 instead.
+    bool Usef64 = TLI.isTypeLegal(MVT::f64) && !Subtarget->is64Bit();
+    if (Usef64)
+      SrcVal = DAG.getNode(ISD::BITCAST, dl, MVT::f64, SrcVal);
+    SrcVal = DAG.getNode(ISD::SCALAR_TO_VECTOR, dl, Usef64 ? MVT::v2f64 : RegVT,
+                              SrcVal);
+
+    return DCI.CombineTo(N, Usef64 ?
+        DAG.getNode(ISD::BITCAST, dl, RegVT, SrcVal) : SrcVal, Chain);
+  }
+
   return SDValue();
 }