[MemorySSA] Make insertDef insert corresponding phi nodes.

Summary:
The original assumption for the insertDef method was that it would not
materialize Defs out of no-where, hence it will not insert phis needed
after inserting a Def.

However, when cloning an instruction (use case used in LICM), we do
materialize Defs "out of no-where". If the block receiving a Def has at
least one other Def, then no processing is needed. If the block just
received its first Def, we must check where Phi placement is needed.
The only new usage of insertDef is in LICM, hence the trigger for the bug.

But the original goal of the method also fails to apply for the move()
method. If we move a Def from the entry point of a diamond to either the
left or right blocks, then the merge block must add a phi.
While this usecase does not currently occur, or may be viewed as an
incorrect transformation, MSSA must behave corectly given the scenario.

Resolves PR40749 and PR40754.

Reviewers: george.burgess.iv

Subscribers: sanjoy, jlebar, Prazek, jdoerfert, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D58652

llvm-svn: 355040

1 files changed, 9 insertions, 9 deletions

diff --git a/llvm/unittests/Analysis/MemorySSATest.cpp b/llvm/unittests/Analysis/MemorySSATest.cpp
index c38124050f0..bfdf37ee190 100644
--- a/llvm/unittests/Analysis/MemorySSATest.cpp
+++ b/llvm/unittests/Analysis/MemorySSATest.cpp
@@ -159,15 +159,15 @@ TEST_F(MemorySSATest, CreateLoadsAndStoreUpdater) {
   MemoryAccess *LeftStoreAccess = Updater.createMemoryAccessInBB(
       LeftStore, nullptr, Left, MemorySSA::Beginning);
   Updater.insertDef(cast<MemoryDef>(LeftStoreAccess), false);
-  // We don't touch existing loads, so we need to create a new one to get a phi
+
+  // MemoryPHI should exist after adding LeftStore.
+  MP = MSSA.getMemoryAccess(Merge);
+  EXPECT_NE(MP, nullptr);
+
   // Add the second load
   B.SetInsertPoint(Merge, Merge->begin());
   LoadInst *SecondLoad = B.CreateLoad(B.getInt8Ty(), PointerArg);
 
-  // MemoryPHI should not already exist.
-  MP = MSSA.getMemoryAccess(Merge);
-  EXPECT_EQ(MP, nullptr);
-
   // Create the load memory access
   MemoryUse *SecondLoadAccess = cast<MemoryUse>(Updater.createMemoryAccessInBB(
       SecondLoad, nullptr, Merge, MemorySSA::Beginning));
@@ -226,14 +226,14 @@ TEST_F(MemorySSATest, CreateALoadUpdater) {
       Updater.createMemoryAccessInBB(SI, nullptr, Left, MemorySSA::Beginning);
   Updater.insertDef(cast<MemoryDef>(StoreAccess));
 
+  // MemoryPHI should be created when inserting the def
+  MemoryPhi *MP = MSSA.getMemoryAccess(Merge);
+  EXPECT_NE(MP, nullptr);
+
   // Add the load
   B.SetInsertPoint(Merge, Merge->begin());
   LoadInst *LoadInst = B.CreateLoad(B.getInt8Ty(), PointerArg);
 
-  // MemoryPHI should not already exist.
-  MemoryPhi *MP = MSSA.getMemoryAccess(Merge);
-  EXPECT_EQ(MP, nullptr);
-
   // Create the load memory acccess
   MemoryUse *LoadAccess = cast<MemoryUse>(Updater.createMemoryAccessInBB(
       LoadInst, nullptr, Merge, MemorySSA::Beginning));