[PassBuilder] Support O0 in default pipelines

[nikic]

Summary

The default and pre-link pipeline builders currently require you to call a separate method for optimization level O0, even though they have perfectly well-defined O0 optimization pipelines.

Accept O0 optimization level and call buildO0DefaultPipeline() internally, so all consumers don't need to repeat this.

[aeubanks]

yeah, the forced -O0 separation doesn't really make sense

[asbirlea]

llvm/lib/Passes/PassBuilderPipelines.cpp

1554–1555

I'm missing why you're not calling buildO0DefaultPipeline for O0 here too.

[nikic]

llvm/lib/Passes/PassBuilderPipelines.cpp

1554–1555

buildPerModuleDefaultPipeline() will call buildO0DefaultPipeline() in this case.

[asbirlea]

llvm/lib/Passes/PassBuilderPipelines.cpp

1554–1555

Ah, right! Thanks!

clang/lib/CodeGen/BackendUtil.cpp

if (std::optional<GCOVOptions> Options =
           });
     if (std::optional<InstrProfOptions> Options =
             getInstrProfOptions(CodeGenOpts, LangOpts))
       PB.registerPipelineStartEPCallback(
           [Options](ModulePassManager &MPM, OptimizationLevel Level) {
             MPM.addPass(InstrProfiling(*Options, false));
           });
 
-    if (CodeGenOpts.OptimizationLevel == 0) {
-      MPM = PB.buildO0DefaultPipeline(Level, IsLTO || IsThinLTO);
-    } else if (IsThinLTO) {
+    if (IsThinLTO) {
       MPM = PB.buildThinLTOPreLinkDefaultPipeline(Level);
     } else if (IsLTO) {
       MPM = PB.buildLTOPreLinkDefaultPipeline(Level);
     } else {
       MPM = PB.buildPerModuleDefaultPipeline(Level);
     }
 
     if (!CodeGenOpts.MemoryProfileOutput.empty()) {

clang/tools/clang-fuzzer/handle-llvm/handle_llvm.cpp

static void RunOptimizationPasses(raw_ostream &OS, Module &M,
   PassBuilder PB;
 
   PB.registerModuleAnalyses(MAM);
   PB.registerCGSCCAnalyses(CGAM);
   PB.registerFunctionAnalyses(FAM);
   PB.registerLoopAnalyses(LAM);
   PB.crossRegisterProxies(LAM, FAM, CGAM, MAM);
 
-  ModulePassManager MPM;
-  if (OL == OptimizationLevel::O0)
-    MPM = PB.buildO0DefaultPipeline(OL);
-  else
-    MPM = PB.buildPerModuleDefaultPipeline(OL);
+  ModulePassManager MPM = PB.buildPerModuleDefaultPipeline(OL);
   MPM.addPass(PrintModulePass(OS));
 
   MPM.run(M, MAM);
 }
 
 // Mimics the opt tool to run an optimization pass over the provided IR
 static std::string OptLLVM(const std::string &IR, CodeGenOpt::Level OLvl) {
   // Create a module that will run the optimization passes

flang/lib/Frontend/FrontendActions.cpp

#include "llvm/Support/Extension.def"
   pb.registerModuleAnalyses(mam);
   pb.registerCGSCCAnalyses(cgam);
   pb.registerFunctionAnalyses(fam);
   pb.registerLoopAnalyses(lam);
   pb.crossRegisterProxies(lam, fam, cgam, mam);
 
   // Create the pass manager.
   llvm::ModulePassManager mpm;
-  if (opts.OptimizationLevel == 0)
-    mpm = pb.buildO0DefaultPipeline(level, opts.PrepareForFullLTO ||
-                                               opts.PrepareForThinLTO);
-  else if (opts.PrepareForFullLTO)
+  if (opts.PrepareForFullLTO)
     mpm = pb.buildLTOPreLinkDefaultPipeline(level);
   else if (opts.PrepareForThinLTO)
     mpm = pb.buildThinLTOPreLinkDefaultPipeline(level);
   else
     mpm = pb.buildPerModuleDefaultPipeline(level);
 
   if (action == BackendActionTy::Backend_EmitBC)
     mpm.addPass(llvm::BitcodeWriterPass(os));

llvm/include/llvm/Passes/PassBuilder.h

public:
   ModulePassManager buildThinLTOPreLinkDefaultPipeline(OptimizationLevel Level);
 
   /// Build an ThinLTO default optimization pipeline to a pass manager.
   ///
   /// This provides a good default optimization pipeline for link-time
   /// optimization and code generation. It is particularly tuned to fit well
   /// when IR coming into the LTO phase was first run through \c
   /// addPreLinkLTODefaultPipeline, and the two coordinate closely.
-  ///
-  /// 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
   buildThinLTODefaultPipeline(OptimizationLevel Level,
                               const ModuleSummaryIndex *ImportSummary);
 
   /// Build a pre-link, LTO-targeting default optimization pipeline to a pass
   /// manager.
   ///
   /// This adds the pre-link optimizations tuned to work well with a later LTO
   /// run. It works to minimize the IR which needs to be analyzed without
   /// making irreversible decisions which could be made better during the LTO
   /// run.
-  ///
-  /// 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 buildLTOPreLinkDefaultPipeline(OptimizationLevel Level);
 
   /// Build an LTO default optimization pipeline to a pass manager.
   ///
   /// This provides a good default optimization pipeline for link-time
   /// optimization and code generation. It is particularly tuned to fit well
   /// when IR coming into the LTO phase was first run through \c
   /// addPreLinkLTODefaultPipeline, and the two coordinate closely.
-  ///
-  /// 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,
                                             ModuleSummaryIndex *ExportSummary);
 
   /// Build an O0 pipeline with the minimal semantically required passes.
   ///
   /// This should only be used for non-LTO and LTO pre-link pipelines.
   ModulePassManager buildO0DefaultPipeline(OptimizationLevel Level,
                                            bool LTOPreLink = false);

llvm/lib/Passes/PassBuilder.cpp

if (startsWithDefaultPipelineAliasPrefix(Name)) {
 
     OptimizationLevel L = StringSwitch<OptimizationLevel>(Matches[2])
                               .Case("O0", OptimizationLevel::O0)
                               .Case("O1", OptimizationLevel::O1)
                               .Case("O2", OptimizationLevel::O2)
                               .Case("O3", OptimizationLevel::O3)
                               .Case("Os", OptimizationLevel::Os)
                               .Case("Oz", OptimizationLevel::Oz);
-    if (L == OptimizationLevel::O0 && Matches[1] != "thinlto" &&
-        Matches[1] != "lto") {
-      MPM.addPass(buildO0DefaultPipeline(L, Matches[1] == "thinlto-pre-link" ||
-                                                Matches[1] == "lto-pre-link"));
-      return Error::success();
-    }
 
     // This is consistent with old pass manager invoked via opt, but
     // inconsistent with clang. Clang doesn't enable loop vectorization
     // but does enable slp vectorization at Oz.
     PTO.LoopVectorization =
         L.getSpeedupLevel() > 1 && L != OptimizationLevel::Oz;
     PTO.SLPVectorization =
         L.getSpeedupLevel() > 1 && L != OptimizationLevel::Oz;

llvm/lib/Passes/PassBuilderPipelines.cpp

if (!LTOPreLink)
     MPM.addPass(RelLookupTableConverterPass());
 
   return MPM;
 }
 
 ModulePassManager
 PassBuilder::buildPerModuleDefaultPipeline(OptimizationLevel Level,
                                            bool LTOPreLink) {
-  assert(Level != OptimizationLevel::O0 &&
-         "Must request optimizations for the default pipeline!");
+  if (Level == OptimizationLevel::O0)
+    return buildO0DefaultPipeline(Level, LTOPreLink);
 
   ModulePassManager MPM;
 
   // Convert @llvm.global.annotations to !annotation metadata.
   MPM.addPass(Annotation2MetadataPass());
 
   // Force any function attributes we want the rest of the pipeline to observe.
   MPM.addPass(ForceFunctionAttrsPass());
PassBuilder::buildPerModuleDefaultPipeline(OptimizationLevel Level,
   if (LTOPreLink)
     addRequiredLTOPreLinkPasses(MPM);
 
   return MPM;
 }
 
 ModulePassManager
 PassBuilder::buildThinLTOPreLinkDefaultPipeline(OptimizationLevel Level) {
-  assert(Level != OptimizationLevel::O0 &&
-         "Must request optimizations for the default pipeline!");
+  if (Level == OptimizationLevel::O0)
+    return buildO0DefaultPipeline(Level, /*LTOPreLink*/true);
 
   ModulePassManager MPM;
 
   // Convert @llvm.global.annotations to !annotation metadata.
   MPM.addPass(Annotation2MetadataPass());
 
   // Force any function attributes we want the rest of the pipeline to observe.
   MPM.addPass(ForceFunctionAttrsPass());
ModulePassManager PassBuilder::buildThinLTODefaultPipeline(
 
   // Emit annotation remarks.
   addAnnotationRemarksPass(MPM);
 
   return MPM;
 }
 
 ModulePassManager
 PassBuilder::buildLTOPreLinkDefaultPipeline(OptimizationLevel Level) {
-  assert(Level != OptimizationLevel::O0 &&
-         "Must request optimizations for the default pipeline!");
   // FIXME: We should use a customized pre-link pipeline!
   return buildPerModuleDefaultPipeline(Level,
                                        /* LTOPreLink */ true);
 }
 
 ModulePassManager
 PassBuilder::buildLTODefaultPipeline(OptimizationLevel Level,
                                      ModuleSummaryIndex *ExportSummary) {
   ModulePassManager MPM;

mlir/lib/ExecutionEngine/OptUtils.cpp

return [optLevel, sizeLevel, targetMachine](Module *m) -> Error {
 
     pb.registerModuleAnalyses(mam);
     pb.registerCGSCCAnalyses(cgam);
     pb.registerFunctionAnalyses(fam);
     pb.registerLoopAnalyses(lam);
     pb.crossRegisterProxies(lam, fam, cgam, mam);
 
     ModulePassManager mpm;
-    if (*ol == OptimizationLevel::O0)
-      mpm.addPass(pb.buildO0DefaultPipeline(*ol));
-    else
-      mpm.addPass(pb.buildPerModuleDefaultPipeline(*ol));
-
     mpm.run(*m, mam);
     return Error::success();
   };
 }

openmp/libomptarget/plugins-nextgen/common/PluginInterface/JIT.cpp

void JITEngine::opt(TargetMachine *TM, TargetLibraryInfoImpl *TLII, Module &M,
 
   // Register all the basic analyses with the managers.
   PB.registerModuleAnalyses(MAM);
   PB.registerCGSCCAnalyses(CGAM);
   PB.registerFunctionAnalyses(FAM);
   PB.registerLoopAnalyses(LAM);
   PB.crossRegisterProxies(LAM, FAM, CGAM, MAM);
 
-  if (OptLevel)
-    MPM.addPass(PB.buildPerModuleDefaultPipeline(getOptLevel(OptLevel)));
-  else
-    MPM.addPass(PB.buildO0DefaultPipeline(getOptLevel(OptLevel)));
-
   MPM.run(M, MAM);
 }
 
 void JITEngine::codegen(TargetMachine *TM, TargetLibraryInfoImpl *TLII,
                         Module &M, raw_pwrite_stream &OS) {
   legacy::PassManager PM;
   PM.add(new TargetLibraryInfoWrapperPass(*TLII));
   MachineModuleInfoWrapperPass *MMIWP = new MachineModuleInfoWrapperPass(