[DAGCombiner] Fix load-store forwarding of indexed loads.

Summary:
Handle extra output from index loads in cases where we wish to
forward a load value directly from a preceeding store.

Fixes PR39571.

Reviewers: peter.smith, rengolin

Subscribers: javed.absar, hiraditya, arphaman, llvm-commits

Differential Revision: https://reviews.llvm.org/D54265

llvm-svn: 346654

1 files changed, 17 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index b6d88ee6a9d..2b6d5286180 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -12866,6 +12866,20 @@ SDValue DAGCombiner::ForwardStoreValueToDirectLoad(LoadSDNode *LD) {
   bool STCoversLD =
       (Offset >= 0) &&
       (Offset * 8 + LDMemType.getSizeInBits() <= STMemType.getSizeInBits());
+
+  auto ReplaceLd = [&](LoadSDNode *LD, SDValue Val, SDValue Chain) -> SDValue {
+    if (LD->isIndexed()) {
+      bool IsSub = (LD->getAddressingMode() == ISD::PRE_DEC ||
+                    LD->getAddressingMode() == ISD::POST_DEC);
+      unsigned Opc = IsSub ? ISD::SUB : ISD::ADD;
+      SDValue Idx = DAG.getNode(Opc, SDLoc(LD), LD->getOperand(1).getValueType(),
+                             LD->getOperand(1), LD->getOperand(2));
+      SDValue Ops[] = {Val, Idx, Chain};
+      return CombineTo(LD, Ops, 3);
+    }
+    return CombineTo(LD, Val, Chain);
+  };
+
   if (!STCoversLD)
     return SDValue();
 
@@ -12873,7 +12887,7 @@ SDValue DAGCombiner::ForwardStoreValueToDirectLoad(LoadSDNode *LD) {
   if (Offset == 0 && LDType == STType && STMemType == LDMemType) {
     // Simple case: Direct non-truncating forwarding
     if (LDType.getSizeInBits() == LDMemType.getSizeInBits())
-      return CombineTo(LD, ST->getValue(), Chain);
+      return ReplaceLd(LD, ST->getValue(), Chain);
     // Can we model the truncate and extension with an and mask?
     if (STType.isInteger() && LDMemType.isInteger() && !STType.isVector() &&
         !LDMemType.isVector() && LD->getExtensionType() != ISD::SEXTLOAD) {
@@ -12883,7 +12897,7 @@ SDValue DAGCombiner::ForwardStoreValueToDirectLoad(LoadSDNode *LD) {
                                                STMemType.getSizeInBits()),
                           SDLoc(ST), STType);
       auto Val = DAG.getNode(ISD::AND, SDLoc(LD), LDType, ST->getValue(), Mask);
-      return CombineTo(LD, Val, Chain);
+      return ReplaceLd(LD, Val, Chain);
     }
   }
 
@@ -12908,7 +12922,7 @@ SDValue DAGCombiner::ForwardStoreValueToDirectLoad(LoadSDNode *LD) {
     }
     if (!extendLoadedValueToExtension(LD, Val))
       continue;
-    return CombineTo(LD, Val, Chain);
+    return ReplaceLd(LD, Val, Chain);
   } while (false);
 
   // On failure, cleanup dead nodes we may have created.