[ThinLTO] Clang changes to utilize new pass to handle chains of aliases

[tejohnson]

Summary

As with NameAnonGlobals, invoke the new CanonicalizeAliases via clang
when using the new PM.

Depends on D54507.

[tejohnson]

Update comment

[tejohnson]

ping on the clang side change as well

[pcc]

LGTM

lib/CodeGen/BackendUtil.cpp

 #include "llvm/Transforms/InstCombine/InstCombine.h"
 #include "llvm/Transforms/Instrumentation.h"
 #include "llvm/Transforms/Instrumentation/BoundsChecking.h"
 #include "llvm/Transforms/Instrumentation/GCOVProfiler.h"
 #include "llvm/Transforms/ObjCARC.h"
 #include "llvm/Transforms/Scalar.h"
 #include "llvm/Transforms/Scalar/GVN.h"
 #include "llvm/Transforms/Utils.h"
+#include "llvm/Transforms/Utils/CanonicalizeAliases.h"
 #include "llvm/Transforms/Utils/NameAnonGlobals.h"
 #include "llvm/Transforms/Utils/SymbolRewriter.h"
 #include <memory>
 using namespace clang;
 using namespace llvm;
 
 namespace {
 
if (CodeGenOpts.OptimizationLevel == 0) {
       // which is just that always inlining occurs.
       MPM.addPass(AlwaysInlinerPass());
 
       // At -O0 we directly run necessary sanitizer passes.
       if (LangOpts.Sanitize.has(SanitizerKind::LocalBounds))
         MPM.addPass(createModuleToFunctionPassAdaptor(BoundsCheckingPass()));
 
       // Lastly, add a semantically necessary pass for LTO.
-      if (IsLTO || IsThinLTO)
+      if (IsLTO || IsThinLTO) {
+        MPM.addPass(CanonicalizeAliasesPass());
         MPM.addPass(NameAnonGlobalPass());
+      }
     } else {
       // Map our optimization levels into one of the distinct levels used to
       // configure the pipeline.
       PassBuilder::OptimizationLevel Level = mapToLevel(CodeGenOpts);
 
       // Register callbacks to schedule sanitizer passes at the appropriate part of
       // the pipeline.
       if (LangOpts.Sanitize.has(SanitizerKind::LocalBounds))
         PB.registerScalarOptimizerLateEPCallback(
             [](FunctionPassManager &FPM, PassBuilder::OptimizationLevel Level) {
               FPM.addPass(BoundsCheckingPass());
             });
       if (Optional<GCOVOptions> Options = getGCOVOptions(CodeGenOpts))
         PB.registerPipelineStartEPCallback([Options](ModulePassManager &MPM) {
           MPM.addPass(GCOVProfilerPass(*Options));
         });
 
       if (IsThinLTO) {
         MPM = PB.buildThinLTOPreLinkDefaultPipeline(
             Level, CodeGenOpts.DebugPassManager);
+        MPM.addPass(CanonicalizeAliasesPass());
         MPM.addPass(NameAnonGlobalPass());
       } else if (IsLTO) {
         MPM = PB.buildLTOPreLinkDefaultPipeline(Level,
                                                 CodeGenOpts.DebugPassManager);
+        MPM.addPass(CanonicalizeAliasesPass());
         MPM.addPass(NameAnonGlobalPass());
       } else {
         MPM = PB.buildPerModuleDefaultPipeline(Level,
                                                CodeGenOpts.DebugPassManager);
       }
     }
   }
 

test/CodeGen/lto-newpm-pipeline.c

 // RUN:   -check-prefix=CHECK-THIN-OPTIMIZED
 // RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm-bc -o /dev/null -fexperimental-new-pass-manager -fdebug-pass-manager -flto=full -Oz %s 2>&1 | FileCheck %s \
 // RUN:   -check-prefix=CHECK-FULL-OPTIMIZED
 // RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm-bc -o /dev/null -fexperimental-new-pass-manager -fdebug-pass-manager -flto=thin -Oz %s 2>&1 | FileCheck %s \
 // RUN:   -check-prefix=CHECK-THIN-OPTIMIZED
 
 // CHECK-FULL-O0: Starting llvm::Module pass manager run.
 // CHECK-FULL-O0: Running pass: AlwaysInlinerPass
+// CHECK-FULL-O0-NEXT: Running pass: CanonicalizeAliasesPass
 // CHECK-FULL-O0-NEXT: Running pass: NameAnonGlobalPass
 // CHECK-FULL-O0-NEXT: Running pass: BitcodeWriterPass
 // CHECK-FULL-O0: Finished llvm::Module pass manager run.
 
 // CHECK-THIN-O0: Starting llvm::Module pass manager run.
 // CHECK-THIN-O0: Running pass: AlwaysInlinerPass
+// CHECK-THIN-O0-NEXT: Running pass: CanonicalizeAliasesPass
 // CHECK-THIN-O0-NEXT: Running pass: NameAnonGlobalPass
 // CHECK-THIN-O0-NEXT: Running pass: ThinLTOBitcodeWriterPass
 // CHECK-THIN-O0: Finished llvm::Module pass manager run.
 
 // TODO: The LTO pre-link pipeline currently invokes
 //       buildPerModuleDefaultPipeline(), which contains LoopVectorizePass.
 //       This may change as the pipeline gets implemented.
 // CHECK-FULL-OPTIMIZED: Starting llvm::Function pass manager run.
 // CHECK-FULL-OPTIMIZED: Running pass: LoopVectorizePass
 // CHECK-FULL-OPTIMIZED: Running pass: BitcodeWriterPass
 
 // The ThinLTO pre-link pipeline shouldn't contain passes like
 // LoopVectorizePass.
 // CHECK-THIN-OPTIMIZED: Starting llvm::Function pass manager run.
 // CHECK-THIN-OPTIMIZED-NOT: Running pass: LoopVectorizePass
+// CHECK-THIN-OPTIMIZED: Running pass: CanonicalizeAliasesPass
 // CHECK-THIN-OPTIMIZED: Running pass: NameAnonGlobalPass
 // CHECK-THIN-OPTIMIZED: Running pass: ThinLTOBitcodeWriterPass
 
 void Foo() {}