[CGData][MachineOutliner] Global Outlining

This commit introduces support for outlining functions across modules using codegen data generated from previous codegen. The codegen data currently manages the outlined hash tree, which records outlining instances that occurred locally in the past.

The machine outliner now operates in one of three modes:
1. CGDataMode::None: This is the default outliner mode that uses the suffix tree to identify (local) outlining candidates within a module. This mode is also used by (full)LTO to maintain optimal behavior with the combined module.
2. CGDataMode::Write (`codegen-data-generate`): This mode is identical to the default mode, but it also publishes the stable hash sequences of instructions in the outlined functions into a local outlined hash tree. It then encodes this into the `__llvm_outline` section, which will be dead-stripped at link time.
3. CGDataMode::Read (`codegen-data-use-path={.cgdata}`): This mode reads a codegen data file (.cgdata) and initializes a global outlined hash tree. This tree is used to generate global outlining candidates. Note that the codegen data file has been post-processed with the raw `__llvm_outline` sections from all native objects using the `llvm-cgdata` tool (or a linker, `LLD`, or a new ThinLTO pipeline later).

Author: kyulee-com

llvm/include/llvm/CodeGen/MachineOutliner.h

@@ -18,6 +18,7 @@
 #include "llvm/CodeGen/LiveRegUnits.h"
 #include "llvm/CodeGen/MachineFunction.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/CodeGen/MachineStableHash.h"
 #include <initializer_list>
 
 namespace llvm {
@@ -274,6 +275,41 @@ struct OutlinedFunction {
   OutlinedFunction() = delete;
   virtual ~OutlinedFunction() = default;
 };
+
+/// The information necessary to create an outlined function that is matched
+/// globally.
+struct GlobalOutlinedFunction : public OutlinedFunction {
+  GlobalOutlinedFunction(OutlinedFunction &OF, unsigned GlobalOccurrenceCount)
+      : OutlinedFunction(OF.Candidates, OF.SequenceSize, OF.FrameOverhead,
+                         OF.FrameConstructionID),
+        GlobalOccurrenceCount(GlobalOccurrenceCount) {}
+
+  unsigned GlobalOccurrenceCount;
+
+  /// Return the number of times that appear globally.
+  /// Global outlining candidate is uniquely created per each match, but this
+  /// might be erased out when it's overlapped with the previous outlining
+  /// instance.
+  unsigned getOccurrenceCount() const override {
+    assert(Candidates.size() <= 1);
+    return Candidates.empty() ? 0 : GlobalOccurrenceCount;
+  }
+
+  /// Return the outlining cost using the global occurrence count
+  /// with the same cost as the first (unique) candidate.
+  unsigned getOutliningCost() const override {
+    assert(Candidates.size() <= 1);
+    unsigned CallOverhead =
+        Candidates.empty()
+            ? 0
+            : Candidates[0].getCallOverhead() * getOccurrenceCount();
+    return CallOverhead + SequenceSize + FrameOverhead;
+  }
+
+  GlobalOutlinedFunction() = delete;
+  ~GlobalOutlinedFunction() = default;
+};
+
 } // namespace outliner
 } // namespace llvm
 

llvm/lib/CodeGen/CMakeLists.txt

@@ -266,6 +266,7 @@ add_llvm_component_library(LLVMCodeGen
   Analysis
   BitReader
   BitWriter
+  CodeGenData
   CodeGenTypes
   Core
   MC