[X86][AVX] Access a scalar float/double as a free extract from a broadcast load (PR43217)

If a fp scalar is loaded and then used as both a scalar and a vector broadcast, perform the load as a broadcast and then extract the scalar for 'free' from the 0th element.

This involved switching the order of the X86ISD::BROADCAST combines so we only convert to X86ISD::BROADCAST_LOAD once all other canonicalizations have been attempted.

Adds a DAGCombinerInfo::recursivelyDeleteUnusedNodes wrapper.

Fixes PR43217

Differential Revision: https://reviews.llvm.org/D68544

llvm-svn: 373871

2 files changed, 29 insertions, 11 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 38fd9742d2d..7ea908437ff 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -761,6 +761,11 @@ CombineTo(SDNode *N, SDValue Res0, SDValue Res1, bool AddTo) {
   return ((DAGCombiner*)DC)->CombineTo(N, Res0, Res1, AddTo);
 }
 
+bool TargetLowering::DAGCombinerInfo::
+recursivelyDeleteUnusedNodes(SDNode *N) {
+  return ((DAGCombiner*)DC)->recursivelyDeleteUnusedNodes(N);
+}
+
 void TargetLowering::DAGCombinerInfo::
 CommitTargetLoweringOpt(const TargetLowering::TargetLoweringOpt &TLO) {
   return ((DAGCombiner*)DC)->CommitTargetLoweringOpt(TLO);
diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 784bf6d58c5..915046048ff 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -33429,8 +33429,19 @@ static SDValue combineTargetShuffle(SDValue N, SelectionDAG &DAG,
     if (Src.getOpcode() == ISD::SCALAR_TO_VECTOR)
       return DAG.getNode(X86ISD::VBROADCAST, DL, VT, Src.getOperand(0));
 
+    // Share broadcast with the longest vector and extract low subvector (free).
+    for (SDNode *User : Src->uses())
+      if (User != N.getNode() &&
+          (User->getOpcode() == X86ISD::VBROADCAST ||
+           User->getOpcode() == X86ISD::VBROADCAST_LOAD) &&
+          User->getValueSizeInBits(0) > VT.getSizeInBits()) {
+        return extractSubVector(SDValue(User, 0), 0, DAG, DL,
+                                VT.getSizeInBits());
+      }
+
     // vbroadcast(scalarload X) -> vbroadcast_load X
-    if (!SrcVT.isVector() && Src.hasOneUse() &&
+    // For float loads, extract other uses of the scalar from the broadcast.
+    if (!SrcVT.isVector() && (Src.hasOneUse() || VT.isFloatingPoint()) &&
         ISD::isNormalLoad(Src.getNode())) {
       LoadSDNode *LN = cast<LoadSDNode>(Src);
       SDVTList Tys = DAG.getVTList(VT, MVT::Other);
@@ -33438,17 +33449,19 @@ static SDValue combineTargetShuffle(SDValue N, SelectionDAG &DAG,
       SDValue BcastLd =
           DAG.getMemIntrinsicNode(X86ISD::VBROADCAST_LOAD, DL, Tys, Ops,
                                   LN->getMemoryVT(), LN->getMemOperand());
-      DAG.ReplaceAllUsesOfValueWith(SDValue(LN, 1), BcastLd.getValue(1));
-      return BcastLd;
-    }
-
-    // Share broadcast with the longest vector and extract low subvector (free).
-    for (SDNode *User : Src->uses())
-      if (User != N.getNode() && User->getOpcode() == X86ISD::VBROADCAST &&
-          User->getValueSizeInBits(0) > VT.getSizeInBits()) {
-        return extractSubVector(SDValue(User, 0), 0, DAG, DL,
-                                VT.getSizeInBits());
+      // If the load value is used only by N, replace it via CombineTo N.
+      bool NoReplaceExtract = Src.hasOneUse();
+      DCI.CombineTo(N.getNode(), BcastLd);
+      if (NoReplaceExtract) {
+        DAG.ReplaceAllUsesOfValueWith(SDValue(LN, 1), BcastLd.getValue(1));
+        DCI.recursivelyDeleteUnusedNodes(LN);
+      } else {
+        SDValue Scl = DAG.getNode(ISD::EXTRACT_VECTOR_ELT, DL, SrcVT, BcastLd,
+                                  DAG.getIntPtrConstant(0, DL));
+        DCI.CombineTo(LN, Scl, BcastLd.getValue(1));
       }
+      return N; // Return N so it doesn't get rechecked!
+    }
 
     return SDValue();
   }