[X86][AVX] Ensure broadcast loads respect dependencies

To allow broadcast loads of a non-zero'th vector element, lowerVectorShuffleAsBroadcast can replace a load with a new load with an adjusted address, but unfortunately we weren't ensuring that the new load respected the same dependencies.

This patch adds a TokenFactor and updates all dependencies of the old load to reference the new load instead.

Bug found during internal testing.

Differential Revision: https://reviews.llvm.org/D25039

llvm-svn: 283070

1 files changed, 11 insertions, 0 deletions

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 1bece04a38d..674aa257db1 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -8683,6 +8683,17 @@ static SDValue lowerVectorShuffleAsBroadcast(const SDLoc &DL, MVT VT,
     V = DAG.getLoad(SVT, DL, Ld->getChain(), NewAddr,
                     DAG.getMachineFunction().getMachineMemOperand(
                         Ld->getMemOperand(), Offset, SVT.getStoreSize()));
+
+    // Make sure the newly-created LOAD is in the same position as Ld in
+    // terms of dependency. We create a TokenFactor for Ld and V,
+    // 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(V.getNode(), 1));
+      DAG.ReplaceAllUsesOfValueWith(SDValue(Ld, 1), NewChain);
+      DAG.UpdateNodeOperands(NewChain.getNode(), SDValue(Ld, 1),
+                             SDValue(V.getNode(), 1));
+    }
   } else if (!BroadcastFromReg) {
     // We can't broadcast from a vector register.
     return SDValue();