[MemorySSA] Extend allowed behavior for simplified instructions.

Summary:
LoopRotate may simplify instructions, leading to the new instructions not having memory accesses created for them.
Allow this behavior, by allowing the new access to be null when the template is null, and looking upwards for the proper defined access when dealing with simplified instructions.

Reviewers: george.burgess.iv

Subscribers: jlebar, Prazek, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D65338

llvm-svn: 367352

1 files changed, 44 insertions, 22 deletions

diff --git a/llvm/lib/Analysis/MemorySSAUpdater.cpp b/llvm/lib/Analysis/MemorySSAUpdater.cpp
index 4c1feee7fd9..42bbe7483b2 100644
--- a/llvm/lib/Analysis/MemorySSAUpdater.cpp
+++ b/llvm/lib/Analysis/MemorySSAUpdater.cpp
@@ -480,29 +480,47 @@ void MemorySSAUpdater::removeDuplicatePhiEdgesBetween(const BasicBlock *From,
   }
 }
 
+static MemoryAccess *getNewDefiningAccessForClone(MemoryAccess *MA,
+                                                  const ValueToValueMapTy &VMap,
+                                                  PhiToDefMap &MPhiMap,
+                                                  bool CloneWasSimplified,
+                                                  MemorySSA *MSSA) {
+  MemoryAccess *InsnDefining = MA;
+  if (MemoryDef *DefMUD = dyn_cast<MemoryDef>(InsnDefining)) {
+    if (!MSSA->isLiveOnEntryDef(DefMUD)) {
+      Instruction *DefMUDI = DefMUD->getMemoryInst();
+      assert(DefMUDI && "Found MemoryUseOrDef with no Instruction.");
+      if (Instruction *NewDefMUDI =
+              cast_or_null<Instruction>(VMap.lookup(DefMUDI))) {
+        InsnDefining = MSSA->getMemoryAccess(NewDefMUDI);
+        if (!CloneWasSimplified)
+          assert(InsnDefining && "Defining instruction cannot be nullptr.");
+        else if (!InsnDefining || isa<MemoryUse>(InsnDefining)) {
+          // The clone was simplified, it's no longer a MemoryDef, look up.
+          auto DefIt = DefMUD->getDefsIterator();
+          // Since simplified clones only occur in single block cloning, a
+          // previous definition must exist, otherwise NewDefMUDI would not
+          // have been found in VMap.
+          assert(DefIt != MSSA->getBlockDefs(DefMUD->getBlock())->begin() &&
+                 "Previous def must exist");
+          InsnDefining = getNewDefiningAccessForClone(
+              &*(--DefIt), VMap, MPhiMap, CloneWasSimplified, MSSA);
+        }
+      }
+    }
+  } else {
+    MemoryPhi *DefPhi = cast<MemoryPhi>(InsnDefining);
+    if (MemoryAccess *NewDefPhi = MPhiMap.lookup(DefPhi))
+      InsnDefining = NewDefPhi;
+  }
+  assert(InsnDefining && "Defining instruction cannot be nullptr.");
+  return InsnDefining;
+}
+
 void MemorySSAUpdater::cloneUsesAndDefs(BasicBlock *BB, BasicBlock *NewBB,
                                         const ValueToValueMapTy &VMap,
                                         PhiToDefMap &MPhiMap,
                                         bool CloneWasSimplified) {
-  auto GetNewDefiningAccess = [&](MemoryAccess *MA) -> MemoryAccess * {
-    MemoryAccess *InsnDefining = MA;
-    if (MemoryUseOrDef *DefMUD = dyn_cast<MemoryUseOrDef>(InsnDefining)) {
-      if (!MSSA->isLiveOnEntryDef(DefMUD)) {
-        Instruction *DefMUDI = DefMUD->getMemoryInst();
-        assert(DefMUDI && "Found MemoryUseOrDef with no Instruction.");
-        if (Instruction *NewDefMUDI =
-                cast_or_null<Instruction>(VMap.lookup(DefMUDI)))
-          InsnDefining = MSSA->getMemoryAccess(NewDefMUDI);
-      }
-    } else {
-      MemoryPhi *DefPhi = cast<MemoryPhi>(InsnDefining);
-      if (MemoryAccess *NewDefPhi = MPhiMap.lookup(DefPhi))
-        InsnDefining = NewDefPhi;
-    }
-    assert(InsnDefining && "Defining instruction cannot be nullptr.");
-    return InsnDefining;
-  };
-
   const MemorySSA::AccessList *Acc = MSSA->getBlockAccesses(BB);
   if (!Acc)
     return;
@@ -519,9 +537,13 @@ void MemorySSAUpdater::cloneUsesAndDefs(BasicBlock *BB, BasicBlock *NewBB,
       if (Instruction *NewInsn =
               dyn_cast_or_null<Instruction>(VMap.lookup(Insn))) {
         MemoryAccess *NewUseOrDef = MSSA->createDefinedAccess(
-            NewInsn, GetNewDefiningAccess(MUD->getDefiningAccess()),
-            CloneWasSimplified ? nullptr : MUD);
-        MSSA->insertIntoListsForBlock(NewUseOrDef, NewBB, MemorySSA::End);
+            NewInsn,
+            getNewDefiningAccessForClone(MUD->getDefiningAccess(), VMap,
+                                         MPhiMap, CloneWasSimplified, MSSA),
+            /*Template=*/CloneWasSimplified ? nullptr : MUD,
+            /*CreationMustSucceed=*/CloneWasSimplified ? false : true);
+        if (NewUseOrDef)
+          MSSA->insertIntoListsForBlock(NewUseOrDef, NewBB, MemorySSA::End);
       }
     }
   }