[DAG] Defer merge store cycle checking to just before merge. NFCI.

llvm-svn: 332489

Author: niravhdave

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -13473,14 +13473,6 @@ bool DAGCombiner::MergeConsecutiveStores(StoreSDNode *St) {
       continue;
     }
 
-    // Check that we can merge these candidates without causing a cycle
-    if (!checkMergeStoreCandidatesForDependencies(StoreNodes,
-                                                  NumConsecutiveStores)) {
-      StoreNodes.erase(StoreNodes.begin(),
-                       StoreNodes.begin() + NumConsecutiveStores);
-      continue;
-    }
-
     // The node with the lowest store address.
     LLVMContext &Context = *DAG.getContext();
     const DataLayout &DL = DAG.getDataLayout();
@@ -13576,6 +13568,12 @@ bool DAGCombiner::MergeConsecutiveStores(StoreSDNode *St) {
         continue;
       }
 
+      // Check that we can merge these candidates without causing a cycle.
+      if (!checkMergeStoreCandidatesForDependencies(StoreNodes, NumElem)) {
+        StoreNodes.erase(StoreNodes.begin(), StoreNodes.begin() + NumElem);
+        continue;
+      }
+
       bool Merged = MergeStoresOfConstantsOrVecElts(
           StoreNodes, MemVT, NumElem, true, UseVector, LastIntegerTrunc);
       RV |= Merged;
@@ -13634,6 +13632,14 @@ bool DAGCombiner::MergeConsecutiveStores(StoreSDNode *St) {
         continue;
       }
 
+      // Check that we can merge these candidates without causing a cycle.
+      if (!checkMergeStoreCandidatesForDependencies(StoreNodes,
+                                                    NumStoresToMerge)) {
+        StoreNodes.erase(StoreNodes.begin(),
+                         StoreNodes.begin() + NumStoresToMerge);
+        continue;
+      }
+
       bool Merged = MergeStoresOfConstantsOrVecElts(
           StoreNodes, MemVT, NumStoresToMerge, false, true, false);
       if (!Merged) {
@@ -13803,6 +13809,12 @@ bool DAGCombiner::MergeConsecutiveStores(StoreSDNode *St) {
       continue;
     }
 
+    // Check that we can merge these candidates without causing a cycle.
+    if (!checkMergeStoreCandidatesForDependencies(StoreNodes, NumElem)) {
+      StoreNodes.erase(StoreNodes.begin(), StoreNodes.begin() + NumElem);
+      continue;
+    }
+
     // Find if it is better to use vectors or integers to load and store
     // to memory.
     EVT JointMemOpVT;