Clarify and make explicit some of the requirements for transforming

mask+shift pairs at the beginning of the ISD::AND case block, and then
hoist the final pattern into a helper function, simplifying and
reflowing it appropriately. This should have no observable behavior
change, but several simplifications fell out of this such as directly
computing the new mask constant, etc.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@147939 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 64 insertions, 52 deletions

diff --git a/lib/Target/X86/X86ISelDAGToDAG.cpp b/lib/Target/X86/X86ISelDAGToDAG.cpp
index 3df6039eaf..326ee8765f 100644
--- a/lib/Target/X86/X86ISelDAGToDAG.cpp
+++ b/lib/Target/X86/X86ISelDAGToDAG.cpp
@@ -788,6 +788,57 @@ static bool FoldMaskAndShiftToExtract(SelectionDAG &DAG, SDValue N,
   return false;
 }
 
+// Transforms "(X << C1) & C2" to "(X & (C2>>C1)) << C1" if safe and if this
+// allows us to fold the shift into this addressing mode. Returns false if the
+// transform succeeded.
+static bool FoldMaskedShiftToScaledMask(SelectionDAG &DAG, SDValue N,
+                                        uint64_t Mask,
+                                        SDValue Shift, SDValue X,
+                                        X86ISelAddressMode &AM) {
+  if (Shift.getOpcode() != ISD::SHL ||
+      !isa<ConstantSDNode>(Shift.getOperand(1)))
+    return true;
+
+  // Not likely to be profitable if either the AND or SHIFT node has more
+  // than one use (unless all uses are for address computation). Besides,
+  // isel mechanism requires their node ids to be reused.
+  if (!N.hasOneUse() || !Shift.hasOneUse())
+    return true;
+
+  // Verify that the shift amount is something we can fold.
+  unsigned ShiftAmt = Shift.getConstantOperandVal(1);
+  if (ShiftAmt != 1 && ShiftAmt != 2 && ShiftAmt != 3)
+    return true;
+
+  EVT VT = N.getValueType();
+  DebugLoc DL = N.getDebugLoc();
+  SDValue NewMask = DAG.getConstant(Mask >> ShiftAmt, VT);
+  SDValue NewAnd = DAG.getNode(ISD::AND, DL, VT, X, NewMask);
+  SDValue NewShift = DAG.getNode(ISD::SHL, DL, VT, NewAnd, Shift.getOperand(1));
+
+  // Insert the new nodes into the topological ordering.
+  if (NewMask.getNode()->getNodeId() == -1 ||
+      NewMask.getNode()->getNodeId() > X.getNode()->getNodeId()) {
+    DAG.RepositionNode(X.getNode(), NewMask.getNode());
+    NewMask.getNode()->setNodeId(X.getNode()->getNodeId());
+  }
+  if (NewAnd.getNode()->getNodeId() == -1 ||
+      NewAnd.getNode()->getNodeId() > Shift.getNode()->getNodeId()) {
+    DAG.RepositionNode(Shift.getNode(), NewAnd.getNode());
+    NewAnd.getNode()->setNodeId(Shift.getNode()->getNodeId());
+  }
+  if (NewShift.getNode()->getNodeId() == -1 ||
+      NewShift.getNode()->getNodeId() > N.getNode()->getNodeId()) {
+    DAG.RepositionNode(N.getNode(), NewShift.getNode());
+    NewShift.getNode()->setNodeId(N.getNode()->getNodeId());
+  }
+  DAG.ReplaceAllUsesWith(N, NewShift);
+
+  AM.Scale = 1 << ShiftAmt;
+  AM.IndexReg = NewAnd;
+  return false;
+}
+
 // Implement some heroics to detect shifts of masked values where the mask can
 // be replaced by extending the shift and undoing that in the addressing mode
 // scale. Patterns such as (shl (srl x, c1), c2) are canonicalized into (and
@@ -1185,13 +1236,17 @@ bool X86DAGToDAGISel::MatchAddressRecursively(SDValue N, X86ISelAddressMode &AM,
     // Perform some heroic transforms on an and of a constant-count shift
     // with a constant to enable use of the scaled offset field.
 
-    SDValue Shift = N.getOperand(0);
-    if (Shift.getNumOperands() != 2) break;
-
     // Scale must not be used already.
     if (AM.IndexReg.getNode() != 0 || AM.Scale != 1) break;
 
+    SDValue Shift = N.getOperand(0);
+    if (Shift.getOpcode() != ISD::SRL && Shift.getOpcode() != ISD::SHL) break;
     SDValue X = Shift.getOperand(0);
+
+    // We only handle up to 64-bit values here as those are what matter for
+    // addressing mode optimizations.
+    if (X.getValueSizeInBits() > 64) break;
+
     ConstantSDNode *C2 = dyn_cast<ConstantSDNode>(N.getOperand(1));
     ConstantSDNode *C1 = dyn_cast<ConstantSDNode>(Shift.getOperand(1));
     if (!C1 || !C2) break;
@@ -1205,55 +1260,12 @@ bool X86DAGToDAGISel::MatchAddressRecursively(SDValue N, X86ISelAddressMode &AM,
     if (!FoldMaskAndShiftToScale(*CurDAG, N, AM))
       return false;
 
-    // Handle "(X << C1) & C2" as "(X & (C2>>C1)) << C1" if safe and if this
-    // allows us to fold the shift into this addressing mode.
-    if (Shift.getOpcode() != ISD::SHL) break;
-
-    // Not likely to be profitable if either the AND or SHIFT node has more
-    // than one use (unless all uses are for address computation). Besides,
-    // isel mechanism requires their node ids to be reused.
-    if (!N.hasOneUse() || !Shift.hasOneUse())
-      break;
-    
-    // Verify that the shift amount is something we can fold.
-    unsigned ShiftCst = C1->getZExtValue();
-    if (ShiftCst != 1 && ShiftCst != 2 && ShiftCst != 3)
-      break;
-    
-    // Get the new AND mask, this folds to a constant.
-    SDValue NewANDMask = CurDAG->getNode(ISD::SRL, dl, N.getValueType(),
-                                         SDValue(C2, 0), SDValue(C1, 0));
-    SDValue NewAND = CurDAG->getNode(ISD::AND, dl, N.getValueType(), X, 
-                                     NewANDMask);
-    SDValue NewSHIFT = CurDAG->getNode(ISD::SHL, dl, N.getValueType(),
-                                       NewAND, SDValue(C1, 0));
-
-    // Insert the new nodes into the topological ordering.
-    if (C1->getNodeId() > X.getNode()->getNodeId()) {
-      CurDAG->RepositionNode(X.getNode(), C1);
-      C1->setNodeId(X.getNode()->getNodeId());
-    }
-    if (NewANDMask.getNode()->getNodeId() == -1 ||
-        NewANDMask.getNode()->getNodeId() > X.getNode()->getNodeId()) {
-      CurDAG->RepositionNode(X.getNode(), NewANDMask.getNode());
-      NewANDMask.getNode()->setNodeId(X.getNode()->getNodeId());
-    }
-    if (NewAND.getNode()->getNodeId() == -1 ||
-        NewAND.getNode()->getNodeId() > Shift.getNode()->getNodeId()) {
-      CurDAG->RepositionNode(Shift.getNode(), NewAND.getNode());
-      NewAND.getNode()->setNodeId(Shift.getNode()->getNodeId());
-    }
-    if (NewSHIFT.getNode()->getNodeId() == -1 ||
-        NewSHIFT.getNode()->getNodeId() > N.getNode()->getNodeId()) {
-      CurDAG->RepositionNode(N.getNode(), NewSHIFT.getNode());
-      NewSHIFT.getNode()->setNodeId(N.getNode()->getNodeId());
-    }
-
-    CurDAG->ReplaceAllUsesWith(N, NewSHIFT);
-    
-    AM.Scale = 1 << ShiftCst;
-    AM.IndexReg = NewAND;
-    return false;
+    // Try to swap the mask and shift to place shifts which can be done as
+    // a scale on the outside of the mask.
+    if (!FoldMaskedShiftToScaledMask(*CurDAG, N, C2->getZExtValue(),
+                                     Shift, X, AM))
+      return false;
+    break;
   }
   }