[X86] Directly form VBROADCAST_LOAD in lowerShuffleAsBroadcast on AVX targets.

If we would emit a VBROADCAST node, we can instead directly emit
a VBROADCAST_LOAD. This allows us to get rid of the special case
to use an f64 load on 32-bit targets for vXi64.

I believe there is more cleanup we can do later in this function,
but I'll do that in follow ups.

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 606df57..d0696c2 100644 (file)
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -12980,14 +12980,6 @@ static SDValue lowerShuffleAsBroadcast(const SDLoc &DL, MVT VT, SDValue V1,
     // is expected to be a win for code size, register pressure, and possibly
     // uops even if the original vector load is not eliminated.
 
-    // 32-bit targets need to load i64 as a f64 and then bitcast the result.
-    if (!Subtarget.is64Bit() && VT.getScalarType() == MVT::i64) {
-      BroadcastVT = MVT::getVectorVT(MVT::f64, VT.getVectorNumElements());
-      Opcode = (BroadcastVT.is128BitVector() && !Subtarget.hasAVX2())
-                   ? X86ISD::MOVDDUP
-                   : Opcode;
-    }
-
     // Reduce the vector load and shuffle to a broadcasted scalar load.
     LoadSDNode *Ld = cast<LoadSDNode>(V);
     SDValue BaseAddr = Ld->getOperand(1);
@@ -12995,6 +12987,21 @@ static SDValue lowerShuffleAsBroadcast(const SDLoc &DL, MVT VT, SDValue V1,
     unsigned Offset = BroadcastIdx * SVT.getStoreSize();
     assert((int)(Offset * 8) == BitOffset && "Unexpected bit-offset");
     SDValue NewAddr = DAG.getMemBasePlusOffset(BaseAddr, Offset, DL);
+
+    // Directly form VBROADCAST_LOAD if we're using VBROADCAST opcode rather
+    // than MOVDDUP.
+    // FIXME: Should we add VBROADCAST_LOAD isel patterns for pre-AVX?
+    if (Opcode == X86ISD::VBROADCAST) {
+      SDVTList Tys = DAG.getVTList(BroadcastVT, MVT::Other);
+      SDValue Ops[] = {Ld->getChain(), NewAddr};
+      V = DAG.getMemIntrinsicNode(
+          X86ISD::VBROADCAST_LOAD, DL, Tys, Ops, SVT,
+          DAG.getMachineFunction().getMachineMemOperand(
+              Ld->getMemOperand(), Offset, SVT.getStoreSize()));
+      DAG.makeEquivalentMemoryOrdering(Ld, V);
+      return DAG.getBitcast(VT, V);
+    }
+    assert(SVT == MVT::f64 && "Unexpected VT!");
     V = DAG.getLoad(SVT, DL, Ld->getChain(), NewAddr,
                     DAG.getMachineFunction().getMachineMemOperand(
                         Ld->getMemOperand(), Offset, SVT.getStoreSize()));