[PM] Add support for building a default AA pipeline to the PassBuilder.

[chandlerc]

Summary

Pretty boring and lame as-is but necessary. This is definitely a place
we'll end up with extension hooks longer term. =]

[davide]

LGTM. Side note, while reviewing it, I noticed there are still residuals of NoAA in-tree.

llvm/InitializePasses.h:void initializeNoAAPass(PassRegistry&);

lib/Passes/PassBuilder.cpp

1115–1119

We need similar logic in lld (we already have a flag, -lto-newpm-aa-pipeline=.

[chandlerc]

lib/Passes/PassBuilder.cpp

1115–1119

Cool! Thanks for the review, and if someone doesn't beat me to it I'll but adding use of this to LLD in my queue.

[davide]

lib/Passes/PassBuilder.cpp

1115–1119

We call the same function (from lib/LTO), so I don't think any real modification is required, but, yeah, adding a test to lld would be cool (or llvm-lto2), if you get to it.

include/llvm/Passes/PassBuilder.h

public:
   ///
   /// Note that \p Level cannot be `O0` here. The pipelines produced are
   /// only intended for use when attempting to optimize code. If frontends
   /// require some transformations for semantic reasons, they should explicitly
   /// build them.
   ModulePassManager buildLTODefaultPipeline(OptimizationLevel Level,
                                             bool DebugLogging = false);
 
+  /// Build the default `AAManager` with the default alias analysis pipeline
+  /// registered.
+  AAManager buildDefaultAAPipeline();
+
   /// \brief Parse a textual pass pipeline description into a \c ModulePassManager.
   ///
   /// The format of the textual pass pipeline description looks something like:
   ///
   ///   module(function(instcombine,sroa),dce,cgscc(inliner,function(...)),...)
   ///
   /// Pass managers have ()s describing the nest structure of passes. All passes
   /// are comma separated. As a special shortcut, if the very first pass is not

lib/Passes/PassBuilder.cpp

ModulePassManager PassBuilder::buildLTODefaultPipeline(OptimizationLevel Level,
   LateFPM.addPass(InstCombinePass());
   LateFPM.addPass(SimplifyCFGPass());
 
   MPM.addPass(createModuleToFunctionPassAdaptor(std::move(LateFPM)));
 
   return MPM;
 }
 
+AAManager PassBuilder::buildDefaultAAPipeline() {
+  AAManager AA;
+
+  // The order in which these are registered determines their priority when
+  // being queried.
+
+  // First we register the basic alias analysis that provides the majority of
+  // per-function local AA logic. This is a stateless, on-demand local set of
+  // AA techniques.
+  AA.registerFunctionAnalysis<BasicAA>();
+
+  // Next we query fast, specialized alias analyses that wrap IR-embedded
+  // information about aliasing.
+  AA.registerFunctionAnalysis<ScopedNoAliasAA>();
+  AA.registerFunctionAnalysis<TypeBasedAA>();
+
+  // Add support for querying global aliasing information when available.
+  // Because this is a module analysis this will use any cached analysis state
+  // available but isn't enough to cause it to be available.
+  // FIXME: Enable once the invalidation logic supports this.
+#if 0
+  AA.registerModuleAnalysis<GlobalsAA>();
+#endif
+
+  return AA;
+}
+
 static Optional<int> parseRepeatPassName(StringRef Name) {
   if (!Name.consume_front("repeat<") || !Name.consume_back(">"))
     return None;
   int Count;
   if (Name.getAsInteger(0, Count) || Count <= 0)
     return None;
   return Count;
 }
else
       // Unknown pass name!
       return false;
   }
 
   return parseModulePassPipeline(MPM, *Pipeline, VerifyEachPass, DebugLogging);
 }
 
 bool PassBuilder::parseAAPipeline(AAManager &AA, StringRef PipelineText) {
+  // If the pipeline just consists of the word 'default' just replace the AA
+  // manager with our default one.
+  if (PipelineText == "default") {
+    AA = buildDefaultAAPipeline();
+    return true;
+  }
+
   while (!PipelineText.empty()) {
     StringRef Name;
     std::tie(Name, PipelineText) = PipelineText.split(',');
     if (!parseAAPassName(AA, Name))
       return false;
   }
 
   return true;
 }

test/Other/new-pass-manager.ll

 ; RUN:     | FileCheck %s --check-prefix=CHECK-AA
 ; CHECK-AA: Starting llvm::Module pass manager run
 ; CHECK-AA: Running pass: RequireAnalysisPass
 ; CHECK-AA: Running analysis: AAManager
 ; CHECK-AA: Running analysis: BasicAA
 ; CHECK-AA: Finished llvm::Module pass manager run
 
 ; RUN: opt -disable-output -disable-verify -debug-pass-manager %s 2>&1 \
+; RUN:     -passes='require<aa>' -aa-pipeline='default' \
+; RUN:     | FileCheck %s --check-prefix=CHECK-AA-DEFAULT
+; CHECK-AA-DEFAULT: Starting llvm::Module pass manager run
+; CHECK-AA-DEFAULT: Running pass: RequireAnalysisPass
+; CHECK-AA-DEFAULT: Running analysis: AAManager
+; CHECK-AA-DEFAULT: Running analysis: BasicAA
+; CHECK-AA-DEFAULT: Running analysis: ScopedNoAliasAA
+; CHECK-AA-DEFAULT: Running analysis: TypeBasedAA
+; CHECK-AA-DEFAULT: Finished llvm::Module pass manager run
+
+; RUN: opt -disable-output -disable-verify -debug-pass-manager %s 2>&1 \
 ; RUN:     -passes='require<memdep>' \
 ; RUN:     | FileCheck %s --check-prefix=CHECK-MEMDEP
 ; CHECK-MEMDEP: Starting llvm::Module pass manager run
 ; CHECK-MEMDEP: Running pass: RequireAnalysisPass
 ; CHECK-MEMDEP: Running analysis: MemoryDependenceAnalysis
 ; CHECK-MEMDEP: Finished llvm::Module pass manager run
 
 ; RUN: opt -disable-output -disable-verify -debug-pass-manager %s 2>&1 \