[IRPrinting] Improve module pass printer to work better with -filter-print-funcs

[twoh]

Summary

Previously module pass printer pass prints the banner even when the module doesn't include any function provided with -filter-print-funcs option. This introduced a lot of noise, especailly with ThinLTO. This diff addresses the issue and makes the banner printed only when the module includes functions in -filter-print-funcs list.

[twoh]

Rebase

[twoh]

Friendly ping!

[twoh]

Friendly ping!

[jdoerfert]

LGTM.

llvm/lib/IR/IRPrintingPasses.cpp

 
 PrintModulePass::PrintModulePass() : OS(dbgs()) {}
 PrintModulePass::PrintModulePass(raw_ostream &OS, const std::string &Banner,
                                  bool ShouldPreserveUseListOrder)
     : OS(OS), Banner(Banner),
       ShouldPreserveUseListOrder(ShouldPreserveUseListOrder) {}
 
 PreservedAnalyses PrintModulePass::run(Module &M, ModuleAnalysisManager &) {
+  if (llvm::isFunctionInPrintList("*")) {
     if (!Banner.empty())
       OS << Banner << "\n";
-  if (llvm::isFunctionInPrintList("*"))
     M.print(OS, nullptr, ShouldPreserveUseListOrder);
+  }
   else {
-    for(const auto &F : M.functions())
-      if (llvm::isFunctionInPrintList(F.getName()))
+    bool BannerPrinted = false;
+    for(const auto &F : M.functions()) {
+      if (llvm::isFunctionInPrintList(F.getName())) {
+        if (!BannerPrinted && !Banner.empty()) {
+          OS << Banner << "\n";
+          BannerPrinted = true;
+        }
         F.print(OS);
       }
+    }
+  }
   return PreservedAnalyses::all();
 }
 
 PrintFunctionPass::PrintFunctionPass() : OS(dbgs()) {}
 PrintFunctionPass::PrintFunctionPass(raw_ostream &OS, const std::string &Banner)
     : OS(OS), Banner(Banner) {}
 
 PreservedAnalyses PrintFunctionPass::run(Function &F,

llvm/test/Other/module-pass-printer.ll

+; Check pass name is only printed once.
+; RUN: opt < %s 2>&1 -forceattrs -disable-output -print-after-all | FileCheck %s 
+; RUN: opt < %s 2>&1 -forceattrs -disable-output -print-after-all -filter-print-funcs=foo,bar | FileCheck %s 
+
+; Check pass name is not printed if a module doesn't include any function specified in -filter-print-funcs.
+; RUN: opt < %s 2>&1 -forceattrs -disable-output -print-after-all -filter-print-funcs=baz | FileCheck %s -allow-empty -check-prefix=EMPTY
+
+; CHECK: *** IR Dump After Force set function attributes ***
+; CHECK-NOT: *** IR Dump After Force set function attributes ***
+; EMPTY-NOT: *** IR Dump After Force set function attributes ***
+
+define void @foo() {
+  ret void
+}
+
+define void @bar() {
+  ret void
+}