[PATCH] D18663: Cleanup Chain Handling in X86ISelLowering

[Nirav Dave via llvm-commits]

niravd created this revision.
niravd added reviewers: RKSimon, spatel.
niravd added a subscriber: llvm-commits.

Previously only users of the first merged load's chain were merged which
potentially allows the merged load to elided from the chain of nodes
chained off of another of the merged loads.

http://reviews.llvm.org/D18663

Files:
  lib/Target/X86/X86ISelLowering.cpp

Index: lib/Target/X86/X86ISelLowering.cpp
===================================================================
--- lib/Target/X86/X86ISelLowering.cpp
+++ lib/Target/X86/X86ISelLowering.cpp
@@ -5776,21 +5776,21 @@
     }
   }
 
-  auto CreateLoad = [&DAG, &DL](EVT VT, LoadSDNode *LDBase) {
+  auto CreateLoad = [&DAG, &DL, NumElems, LoadMask, Elts](EVT VT,
+                                                          LoadSDNode *LDBase) {
     SDValue NewLd = DAG.getLoad(VT, DL, LDBase->getChain(),
                                 LDBase->getBasePtr(), LDBase->getPointerInfo(),
-                                LDBase->isVolatile(), LDBase->isNonTemporal(),
+                                false /*isVolatile*/, LDBase->isNonTemporal(),
                                 LDBase->isInvariant(), LDBase->getAlignment());
-
-    if (LDBase->hasAnyUseOfValue(1)) {
-      SDValue NewChain =
-          DAG.getNode(ISD::TokenFactor, DL, MVT::Other, SDValue(LDBase, 1),
-                      SDValue(NewLd.getNode(), 1));
-      DAG.ReplaceAllUsesOfValueWith(SDValue(LDBase, 1), NewChain);
-      DAG.UpdateNodeOperands(NewChain.getNode(), SDValue(LDBase, 1),
-                             SDValue(NewLd.getNode(), 1));
-    }
-
+    // all references to chain for each component load should now point
+    // to new Load's chain
+    for (unsigned i = 0; i < NumElems; ++i)
+      if (LoadMask[i]) {
+        SDValue Elt = peekThroughBitcasts(Elts[i]);
+        LoadSDNode *Ld = cast<LoadSDNode>(Elt);
+        DAG.ReplaceAllUsesOfValueWith(SDValue(Ld, 1),
+                                      SDValue(NewLd.getNode(), 1));
+      }
     return NewLd;
   };
 
@@ -5848,18 +5848,15 @@
                                   false/*isVolatile*/, true/*ReadMem*/,
                                   false/*WriteMem*/);
 
-      // Make sure the newly-created LOAD is in the same position as LDBase in
-      // terms of dependency. We create a TokenFactor for LDBase and ResNode,
-      // and update uses of LDBase's output chain to use the TokenFactor.
-      if (LDBase->hasAnyUseOfValue(1)) {
-        SDValue NewChain =
-            DAG.getNode(ISD::TokenFactor, DL, MVT::Other, SDValue(LDBase, 1),
-                        SDValue(ResNode.getNode(), 1));
-        DAG.ReplaceAllUsesOfValueWith(SDValue(LDBase, 1), NewChain);
-        DAG.UpdateNodeOperands(NewChain.getNode(), SDValue(LDBase, 1),
-                               SDValue(ResNode.getNode(), 1));
-      }
-
+      // all references to chain for each component load should now
+      // point to new Load's chain
+      for (unsigned i = 0; i < NumElems; ++i)
+        if (LoadMask[i]) {
+          SDValue Elt = peekThroughBitcasts(Elts[i]);
+          LoadSDNode *Ld = cast<LoadSDNode>(Elt);
+          DAG.ReplaceAllUsesOfValueWith(SDValue(Ld, 1),
+                                        SDValue(ResNode.getNode(), 1));
+        }
       return DAG.getBitcast(VT, ResNode);
     }
   }
@@ -24046,16 +24043,9 @@
                                   false/*WriteMem*/);
 
         // Make sure the newly-created LOAD is in the same position as Ld in
-        // terms of dependency. We create a TokenFactor for Ld and ResNode,
-        // and update uses of Ld's output chain to use the TokenFactor.
-        if (Ld->hasAnyUseOfValue(1)) {
-          SDValue NewChain = DAG.getNode(ISD::TokenFactor, dl, MVT::Other,
-                             SDValue(Ld, 1), SDValue(ResNode.getNode(), 1));
-          DAG.ReplaceAllUsesOfValueWith(SDValue(Ld, 1), NewChain);
-          DAG.UpdateNodeOperands(NewChain.getNode(), SDValue(Ld, 1),
-                                 SDValue(ResNode.getNode(), 1));
-        }
-
+        // terms of chain dependency.
+        DAG.ReplaceAllUsesOfValueWith(SDValue(Ld, 1),
+                                      SDValue(ResNode.getNode(), 1));
         return DAG.getBitcast(VT, ResNode);
       }
     }


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