[EarlyCSE] Explicitly require AAResultsWrapperPass.

[fhahn]

Summary

The MemorySSAWrapperPass depends on AAResultsWrapperPass and if
MemorySSA is preserved but AAResultsWrapperPass is not, this could lead
to a crash when updating the last user of the MemorySSAWrapperPass.

Alternatively AAResultsWrapperPass could be marked preserved by GVN, but
I am not sure if that would be safe. I am not sure what is required in
order to preserve AAResultsWrapperPass. At the moment, it seems like a
couple of passes that do similar transforms to GVN are preserving it.

llvm/lib/Transforms/Scalar/EarlyCSE.cpp

public:
   }
 
   void getAnalysisUsage(AnalysisUsage &AU) const override {
     AU.addRequired<AssumptionCacheTracker>();
     AU.addRequired<DominatorTreeWrapperPass>();
     AU.addRequired<TargetLibraryInfoWrapperPass>();
     AU.addRequired<TargetTransformInfoWrapperPass>();
     if (UseMemorySSA) {
+      AU.addRequired<AAResultsWrapperPass>();
       AU.addRequired<MemorySSAWrapperPass>();
       AU.addPreserved<MemorySSAWrapperPass>();
     }
     AU.addPreserved<GlobalsAAWrapperPass>();
     AU.addPreserved<AAResultsWrapperPass>();
     AU.setPreservesCFG();
   }
 };
FunctionPass *llvm::createEarlyCSEPass(bool UseMemorySSA) {
   else
     return new EarlyCSELegacyPass();
 }
 
 INITIALIZE_PASS_BEGIN(EarlyCSEMemSSALegacyPass, "early-cse-memssa",
                       "Early CSE w/ MemorySSA", false, false)
 INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
+INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
 INITIALIZE_PASS_DEPENDENCY(MemorySSAWrapperPass)
 INITIALIZE_PASS_END(EarlyCSEMemSSALegacyPass, "early-cse-memssa",
                     "Early CSE w/ MemorySSA", false, false)

llvm/lib/Transforms/Scalar/GVN.cpp

public:
   void getAnalysisUsage(AnalysisUsage &AU) const override {
     AU.addRequired<AssumptionCacheTracker>();
     AU.addRequired<DominatorTreeWrapperPass>();
     AU.addRequired<TargetLibraryInfoWrapperPass>();
     AU.addRequired<LoopInfoWrapperPass>();
     if (Impl.isMemDepEnabled())
       AU.addRequired<MemoryDependenceWrapperPass>();
     AU.addRequired<AAResultsWrapperPass>();
-
     AU.addPreserved<DominatorTreeWrapperPass>();
     AU.addPreserved<GlobalsAAWrapperPass>();
     AU.addPreserved<TargetLibraryInfoWrapperPass>();
     AU.addPreserved<LoopInfoWrapperPass>();
     AU.addRequired<OptimizationRemarkEmitterWrapperPass>();
     AU.addPreserved<MemorySSAWrapperPass>();
   }
 

llvm/test/Transforms/EarlyCSE/reuse-preserved-memoryssa.ll

+; RUN: opt -memoryssa -gvn -early-cse-memssa %s -S | FileCheck %s
+
+; CHECK: define void @foo(
+
+define void @foo() {
+  ret void
+}