[NewPM] Bail from PassManager::run() if there are no passes

[aeubanks]

Summary

With D89158, we have the possibility of creating empty pass managers due
to callbacks choosing to not add passes under -O0. e.g. Polly can add
EP callbacks but not add any passes. This affects some tests that use
-debug-pass-manager, like the one fixed in 8eb338a92a4e.

[nathanchance]

Thank you for the quick fix, this resolves my reported issue. I can approve if need be but it would probably be better for there to be other eyes on this :)

[MaskRay]

LGTM.

[aeubanks]

Actually this causes the test to fail without polly since now there's no output since it's just an empty module pass manager. Will revert original change.

llvm/include/llvm/IR/PassManager.h

public:
   }
 
   /// Run all of the passes in this manager over the given unit of IR.
   /// ExtraArgs are passed to each pass.
   PreservedAnalyses run(IRUnitT &IR, AnalysisManagerT &AM,
                         ExtraArgTs... ExtraArgs) {
     PreservedAnalyses PA = PreservedAnalyses::all();
 
+    if (Passes.empty())
+      return PA;
+
     // Request PassInstrumentation from analysis manager, will use it to run
     // instrumenting callbacks for the passes later.
     // Here we use std::tuple wrapper over getResult which helps to extract
     // AnalysisManager's arguments out of the whole ExtraArgs set.
     PassInstrumentation PI =
         detail::getAnalysisResult<PassInstrumentationAnalysis>(
             AM, IR, std::tuple<ExtraArgTs...>(ExtraArgs...));
 

llvm/test/Other/new-pass-manager.ll

 ; RUN: opt -disable-output -disable-verify -debug-pass-manager %s 2>&1 \
 ; RUN:     -passes='require<callgraph>' \
 ; RUN:     | FileCheck %s --check-prefix=CHECK-CALLGRAPH
 ; CHECK-CALLGRAPH: Starting llvm::Module pass manager run
 ; CHECK-CALLGRAPH: Running pass: RequireAnalysisPass
 ; CHECK-CALLGRAPH: Running analysis: CallGraphAnalysis
 ; CHECK-CALLGRAPH: Finished llvm::Module pass manager run
 
-;; If Polly is enabled, registerPollyPasses adds an ep-vectorizer-start callback.
-;; There may or may not be a function pass manager run.
-;; Add a no-op-function to unify the two cases.
 ; RUN: opt -disable-output -disable-verify -debug-pass-manager \
-; RUN:     -passes='default<O0>' -passes-ep-vectorizer-start=no-op-function %s 2>&1 \
+; RUN:     -passes='default<O0>' %s 2>&1 \
 ; RUN:     | FileCheck %s --check-prefix=CHECK-O0
 ; CHECK-O0: Starting llvm::Module pass manager run
 ; CHECK-O0-NEXT: Running analysis: InnerAnalysisManagerProxy<{{.*}}>
-; CHECK-O0-NEXT: Starting llvm::Function pass manager run
-; CHECK-O0-NEXT: Running pass: NoOpFunctionPass on foo
-; CHECK-O0-NEXT: Finished llvm::Function pass manager run
 ; CHECK-O0-NEXT: Finished llvm::Module pass manager run
 
 ; RUN: opt -disable-output -disable-verify -debug-pass-manager \
 ; RUN:     -passes='repeat<3>(no-op-module)' %s 2>&1 \
 ; RUN:     | FileCheck %s --check-prefix=CHECK-REPEAT-MODULE-PASS
 ; CHECK-REPEAT-MODULE-PASS: Starting llvm::Module pass manager run
 ; CHECK-REPEAT-MODULE-PASS-NEXT: Running pass: RepeatedPass
 ; CHECK-REPEAT-MODULE-PASS-NEXT: Starting llvm::Module pass manager run