X86: when constructing VZEXT_LOAD from other loads, makes sure its output

chain is correctly setup.

As an example, if the original load must happen before later stores, we need
to make sure the constructed VZEXT_LOAD is constrained to be before the stores.

rdar://12684358

llvm-svn: 167859

1 files changed, 12 insertions, 0 deletions

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index b35fb514bf9..025970370c5 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -14203,6 +14203,18 @@ static SDValue PerformShuffleCombine256(SDNode *N, SelectionDAG &DAG,
                                   Ld->getAlignment(),
                                   false/*isVolatile*/, true/*ReadMem*/,
                                   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));
+        }
+
         return DAG.getNode(ISD::BITCAST, dl, VT, ResNode);
       }
     }