Interface to attach maximum function count from PGO to module as module flags.

[eraman]

Summary

This provides interface to get and set maximum function counts to Module. This would allow things like determination of function hotness. The actual setting of this max function count will have to be done in clang.

[davidxl]

I think the inliner/indirect call promoter also needs another meta data at the module level -- that is the max internal BB count (of the program) .

In the longer term, we also need to design better program summary information such as bb counter histogram with respect to exec freq -- but for now, max BB count would be sufficient.

lib/IR/Module.cpp

502

Format -- put return in a new line.

[dnovillo]

How is this going to interact with SamplePGO? Currently, I'm testing a change that adds the InlineHint attribute for functions that globally collected a fraction of samples greater than a given threshold. Likewise, for functions that fall below another threshold, they receive the Cold attribute.

The API talks in terms of function counts, how is this related to the entry count I added earlier? What would SamplePGO have to do here?

Thanks.

[eraman]

lib/IR/Module.cpp

502

clang-format suggests I have the return on the same line.

[davidxl]

use clang-format -style LLVM

David

[eraman]

Ran clang-format with the right options.

[davidxl]

lgtm.

David

include/llvm/IR/Module.h

 /// @file
 /// Module.h This file contains the declarations for the Module class.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_IR_MODULE_H
 #define LLVM_IR_MODULE_H
 
+#include <system_error>
+#include "llvm/ADT/Optional.h"
 #include "llvm/ADT/iterator_range.h"
 #include "llvm/IR/Comdat.h"
 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/GlobalAlias.h"
 #include "llvm/IR/GlobalVariable.h"
 #include "llvm/IR/Metadata.h"
 #include "llvm/Support/CBindingWrapping.h"
 #include "llvm/Support/CodeGen.h"
 #include "llvm/Support/DataTypes.h"
-#include <system_error>
 
 namespace llvm {
 class FunctionType;
 class GVMaterializer;
 class LLVMContext;
 class RandomNumberGenerator;
 class StructType;
 

 /// @{
 
   /// \brief Returns the PIC level (small or large model)
   PICLevel::Level getPICLevel() const;
 
   /// \brief Set the PIC level (small or large model)
   void setPICLevel(PICLevel::Level PL);
 /// @}
+
+  /// @name Utility functions for querying and setting PGO counts
+  /// @{
+
+  /// \brief Set maximum function count in PGO mode
+  void setMaximumFunctionCount(uint64_t);
+
+  /// \brief Returns maximum function count in PGO mode
+  Optional<uint64_t> getMaximumFunctionCount();
+  /// @}
 };
 
 /// An raw_ostream inserter for modules.
 inline raw_ostream &operator<<(raw_ostream &O, const Module &M) {
   M.print(O, nullptr);
   return O;
 }
 

lib/IR/Module.cpp

PICLevel::Level Module::getPICLevel() const {
 
   return static_cast<PICLevel::Level>(
       cast<ConstantInt>(Val->getValue())->getZExtValue());
 }
 
 void Module::setPICLevel(PICLevel::Level PL) {
   addModuleFlag(ModFlagBehavior::Error, "PIC Level", PL);
 }
+
+void Module::setMaximumFunctionCount(uint64_t Count) {
+  addModuleFlag(ModFlagBehavior::Error, "MaxFunctionCount", Count);
+}
+
+Optional<uint64_t> Module::getMaximumFunctionCount() {
+  auto *Val =
+      cast_or_null<ConstantAsMetadata>(getModuleFlag("MaxFunctionCount"));
+  if (!Val) return None;
+  return cast<ConstantInt>(Val->getValue())->getZExtValue();
+}