[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

include/llvm/Analysis/MemorySSA.h

@@ -830,7 +830,8 @@ protected:
   void insertIntoListsBefore(MemoryAccess *, const BasicBlock *,
                              AccessList::iterator);
   MemoryUseOrDef *createDefinedAccess(Instruction *, MemoryAccess *,
-                                      const MemoryUseOrDef *Template = nullptr);
+                                      const MemoryUseOrDef *Template = nullptr,
+                                      bool CreationMustSucceed = true);
 
 private:
   template <class AliasAnalysisType> class ClobberWalkerBase;

lib/Analysis/MemorySSA.cpp

@@ -1687,13 +1687,15 @@ MemoryPhi *MemorySSA::createMemoryPhi(BasicBlock *BB) {
 
 MemoryUseOrDef *MemorySSA::createDefinedAccess(Instruction *I,
                                                MemoryAccess *Definition,
-                                               const MemoryUseOrDef *Template) {
+                                               const MemoryUseOrDef *Template,
+                                               bool CreationMustSucceed) {
   assert(!isa<PHINode>(I) && "Cannot create a defined access for a PHI");
   MemoryUseOrDef *NewAccess = createNewAccess(I, AA, Template);
-  assert(
-      NewAccess != nullptr &&
-      "Tried to create a memory access for a non-memory touching instruction");
-  NewAccess->setDefiningAccess(Definition);
+  if (CreationMustSucceed)
+    assert(NewAccess != nullptr && "Tried to create a memory access for a "
+                                   "non-memory touching instruction");
+  if (NewAccess)
+    NewAccess->setDefiningAccess(Definition);
   return NewAccess;
 }
 

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);
       }
     }
   }

test/Analysis/MemorySSA/loop-rotate-simplified-clone.ll

@@ -0,0 +1,29 @@
+; RUN: opt -verify-memoryssa -enable-mssa-loop-dependency -loop-rotate %s -S | FileCheck %s 
+; REQUIRES: asserts
+
+; CHECK-LABEL: @test()
+define dso_local void @test() {
+entry:
+  br label %preheader
+
+preheader:
+  br label %l39
+
+l39:
+  %v40 = phi float (float)* [ @foo, %preheader ], [ %v43, %crit_edge ]
+  %v41 = call float %v40(float undef)
+  %v42 = load i32, i32* undef, align 8
+  br i1 undef, label %crit_edge, label %loopexit
+
+crit_edge:
+  %v43 = load float (float)*, float (float)** undef, align 8
+  br label %l39
+
+loopexit:
+  unreachable
+}
+
+; Function Attrs: readnone
+declare dso_local float @foo(float) #0 align 32
+
+attributes #0 = { readnone }