[ORE] Add diagnostics hotness threshold

[modocache]

Summary

Add an option to prevent diagnostics that do not meet a minimum hotness
threshold from being output. When generating optimization remarks for
large codebases with a ton of cold code paths, this option can be used
to limit the optimization remark output at a reasonable size. Discussion of
this change can be read here:
http://lists.llvm.org/pipermail/llvm-dev/2017-June/114377.html

[anemet]

Great!

include/llvm/IR/LLVMContext.h

196–199

What's the difference between None and 0?

lib/Analysis/OptimizationDiagnosticInfo.cpp

159–165

You need to add the same code to MachineOptimizationRemarkEmitter::emit() too.

[modocache]

include/llvm/IR/LLVMContext.h

196–199

I had originally thought that there should be a distinction between "the threshold has been set to zero" and "the threshold has not been set", but taking another look at this patch and the one to Clang, I realize there isn't a need for it. I'll remove the Optional<> here, good call!

lib/Analysis/OptimizationDiagnosticInfo.cpp

159–165

Oh, good catch, thank you! Do you know if there's an existing test for MachineOptimizationRemarkEmitter?

[anemet]

lib/Analysis/OptimizationDiagnosticInfo.cpp

159–165

There are a few, look for pass-remarks under test/CodeGen. The one I originally added is test/CodeGen/AArch64/arm64-spill-remarks.ll.

[modocache]

Add hotness threshold check to MachineOptimizationRemarkEmitter, and change the threshold attribute type for LLVMContext from an optional unsigned to just an unsigned.

[modocache]

Add tests for the MachineOptimizationRemarkEmitter codepath, to test/CodeGen/AArch64/arm64-spill-remarks.ll.

[anemet]

LGTM now, thanks!

[modocache]

Great, thank you!

include/llvm/IR/LLVMContext.h

public:
 
   /// \brief Return if a code hotness metric should be included in optimization
   /// diagnostics.
   bool getDiagnosticsHotnessRequested() const;
   /// \brief Set if a code hotness metric should be included in optimization
   /// diagnostics.
   void setDiagnosticsHotnessRequested(bool Requested);
 
+  /// \brief Return the minimum hotness value a diagnostic would need in order
+  /// to be included in optimization diagnostics. If there is no minimum, this
+  /// returns None.
+  Optional<uint64_t> getDiagnosticsHotnessThreshold() const;
+
+  /// \brief Set the minimum hotness value a diagnostic needs in order to be
+  /// included in optimization diagnostics.
+  void setDiagnosticsHotnessThreshold(uint64_t Threshold);
+
   /// \brief Return the YAML file used by the backend to save optimization
   /// diagnostics.  If null, diagnostics are not saved in a file but only
   /// emitted via the diagnostic handler.
   yaml::Output *getDiagnosticsOutputFile();
   /// Set the diagnostics output file used for optimization diagnostics.
   ///
   /// By default or if invoked with null, diagnostics are not saved in a file
   /// but only emitted via the diagnostic handler.  Even if an output file is

lib/Analysis/OptimizationDiagnosticInfo.cpp

if (V)
     OptDiag.setHotness(computeHotness(V));
 }
 
 void OptimizationRemarkEmitter::emit(
     DiagnosticInfoOptimizationBase &OptDiagBase) {
   auto &OptDiag = cast<DiagnosticInfoIROptimization>(OptDiagBase);
   computeHotness(OptDiag);
 
+  // If a diagnostic has a hotness value, then only emit it if its hotness
+  // meets the threshold.
+  auto Threshold = F->getContext().getDiagnosticsHotnessThreshold();
+  if (OptDiag.getHotness() && Threshold &&
+      *OptDiag.getHotness() < *Threshold) {
+    return;
+  }
+
   yaml::Output *Out = F->getContext().getDiagnosticsOutputFile();
   if (Out) {
     auto *P = const_cast<DiagnosticInfoOptimizationBase *>(&OptDiagBase);
     *Out << P;
   }
   // FIXME: now that IsVerbose is part of DI, filtering for this will be moved
   // from here to clang.
   if (!OptDiag.isVerbose() || shouldEmitVerbose())

lib/IR/LLVMContext.cpp

 
 void LLVMContext::setDiagnosticsHotnessRequested(bool Requested) {
   pImpl->DiagnosticsHotnessRequested = Requested;
 }
 bool LLVMContext::getDiagnosticsHotnessRequested() const {
   return pImpl->DiagnosticsHotnessRequested;
 }
 
+void LLVMContext::setDiagnosticsHotnessThreshold(uint64_t Threshold) {
+  pImpl->DiagnosticsHotnessThreshold = Threshold;
+}
+Optional<uint64_t> LLVMContext::getDiagnosticsHotnessThreshold() const {
+  return pImpl->DiagnosticsHotnessThreshold;
+}
+
 yaml::Output *LLVMContext::getDiagnosticsOutputFile() {
   return pImpl->DiagnosticsOutputFile.get();
 }
 
 void LLVMContext::setDiagnosticsOutputFile(std::unique_ptr<yaml::Output> F) {
   pImpl->DiagnosticsOutputFile = std::move(F);
 }
 

lib/IR/LLVMContextImpl.h

public:
   
   LLVMContext::InlineAsmDiagHandlerTy InlineAsmDiagHandler = nullptr;
   void *InlineAsmDiagContext = nullptr;
 
   LLVMContext::DiagnosticHandlerTy DiagnosticHandler = nullptr;
   void *DiagnosticContext = nullptr;
   bool RespectDiagnosticFilters = false;
   bool DiagnosticsHotnessRequested = false;
+  Optional<uint64_t> DiagnosticsHotnessThreshold = None;
   std::unique_ptr<yaml::Output> DiagnosticsOutputFile;
 
   LLVMContext::YieldCallbackTy YieldCallback = nullptr;
   void *YieldOpaqueHandle = nullptr;
 
   using IntMapTy =
       DenseMap<APInt, std::unique_ptr<ConstantInt>, DenseMapAPIntKeyInfo>;
   IntMapTy IntConstants;

test/Transforms/Inline/optimization-remarks-yaml.ll

-; RUN: opt < %s -S -inline -pass-remarks-missed=inline -pass-remarks-with-hotness \
+; RUN: opt < %s -S -inline -pass-remarks-missed=inline \
+; RUN:     -pass-remarks-with-hotness -pass-remarks-hotness-threshold 15 \
 ; RUN:     -pass-remarks-output=%t 2>&1 | FileCheck %s
 ; RUN: cat %t | FileCheck -check-prefix=YAML %s
 ; RUN: opt < %s -S -inline -pass-remarks-with-hotness -pass-remarks-output=%t
 ; RUN: cat %t | FileCheck -check-prefix=YAML %s
+;
+; Verify that remarks that don't meet the hotness threshold are not output.
+; RUN: opt < %s -S -inline -pass-remarks-missed=inline \
+; RUN:     -pass-remarks-with-hotness -pass-remarks-hotness-threshold 100 \
+; RUN:     -pass-remarks-output=%t.threshold 2>&1 | \
+; RUN:     FileCheck -check-prefix=THRESHOLD %s
+; RUN: test ! -s %t.threshold
+; RUN: opt < %s -S -inline \
+; RUN:     -pass-remarks-with-hotness -pass-remarks-hotness-threshold 100 \
+; RUN:     -pass-remarks-output=%t.threshold
+; The remarks output file should be empty.
+; RUN: test ! -s %t.threshold
 
 ; Check the YAML file generated for inliner remarks for this program:
 ;
 ;   1  int foo();
 ;   2  int bar();
 ;   3
 ;   4  int baz() {
 ;   5    return foo() + bar();

 ; YAML-NEXT: Args:
 ; YAML-NEXT:   - Callee: bar
 ; YAML-NEXT:   - String: ' will not be inlined into '
 ; YAML-NEXT:   - Caller: baz
 ; YAML-NEXT:     DebugLoc:        { File: /tmp/s.c, Line: 4, Column: 0 }
 ; YAML-NEXT:   - String: ' because its definition is unavailable'
 ; YAML-NEXT: ...
 
+; No remarks should be output, since none meet the threshold.
+; THRESHOLD-NOT: remark
+
 ; ModuleID = '/tmp/s.c'
 source_filename = "/tmp/s.c"
 target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-apple-macosx10.11.0"
 
 ; Function Attrs: nounwind ssp uwtable
 define i32 @"\01baz"() !dbg !7 !prof !14 {
 entry:

tools/llc/llc.cpp

 
 static cl::list<std::string> IncludeDirs("I", cl::desc("include search path"));
 
 static cl::opt<bool> PassRemarksWithHotness(
     "pass-remarks-with-hotness",
     cl::desc("With PGO, include profile count in optimization remarks"),
     cl::Hidden);
 
+static cl::opt<unsigned> PassRemarksHotnessThreshold(
+    "pass-remarks-hotness-threshold",
+    cl::desc("Minimum profile count required for an optimization remark to be output"),
+    cl::Hidden);
+
 static cl::opt<std::string>
     RemarksFilename("pass-remarks-output",
                     cl::desc("YAML output filename for pass remarks"),
                     cl::value_desc("filename"));
 
 namespace {
 static ManagedStatic<std::vector<std::string>> RunPassNames;
 
int main(int argc, char **argv) {
   // Set a diagnostic handler that doesn't exit on the first error
   bool HasError = false;
   Context.setDiagnosticHandler(DiagnosticHandler, &HasError);
   Context.setInlineAsmDiagnosticHandler(InlineAsmDiagHandler, &HasError);
 
   if (PassRemarksWithHotness)
     Context.setDiagnosticsHotnessRequested(true);
 
+  if (PassRemarksHotnessThreshold)
+    Context.setDiagnosticsHotnessThreshold(PassRemarksHotnessThreshold);
+
   std::unique_ptr<tool_output_file> YamlFile;
   if (RemarksFilename != "") {
     std::error_code EC;
     YamlFile = llvm::make_unique<tool_output_file>(RemarksFilename, EC,
                                                    sys::fs::F_None);
     if (EC) {
       errs() << EC.message() << '\n';
       return 1;

tools/opt/opt.cpp

static cl::opt<bool> Coroutines(
   cl::desc("Enable coroutine passes."),
   cl::init(false), cl::Hidden);
 
 static cl::opt<bool> PassRemarksWithHotness(
     "pass-remarks-with-hotness",
     cl::desc("With PGO, include profile count in optimization remarks"),
     cl::Hidden);
 
+static cl::opt<unsigned> PassRemarksHotnessThreshold(
+    "pass-remarks-hotness-threshold",
+    cl::desc("Minimum profile count required for an optimization remark to be output"),
+    cl::Hidden);
+
 static cl::opt<std::string>
     RemarksFilename("pass-remarks-output",
                     cl::desc("YAML output filename for pass remarks"),
                     cl::value_desc("filename"));
 
 static inline void addPass(legacy::PassManagerBase &PM, Pass *P) {
   // Add the pass to the pass manager...
   PM.add(P);
#endif
 
   Context.setDiscardValueNames(DiscardValueNames);
   if (!DisableDITypeMap)
     Context.enableDebugTypeODRUniquing();
 
   if (PassRemarksWithHotness)
     Context.setDiagnosticsHotnessRequested(true);
 
+  if (PassRemarksHotnessThreshold)
+    Context.setDiagnosticsHotnessThreshold(PassRemarksHotnessThreshold);
+
   std::unique_ptr<tool_output_file> YamlFile;
   if (RemarksFilename != "") {
     std::error_code EC;
     YamlFile = llvm::make_unique<tool_output_file>(RemarksFilename, EC,
                                                    sys::fs::F_None);
     if (EC) {
       errs() << EC.message() << '\n';
       return 1;