[BOLT][NFC] Keep input icount for disassembled functions

[aaupov]

Preserve input instruction count for profile density computation (#101094).
Set it right after disassembly, if it has succeeded.

This way, we address two issues:

• overhead: otherwise, we'd need to iterate over basic blocks to get
  instruction count.
• availability: non-simple functions in non-relocation mode (=BOLT split
  functions in BOLTed binaries) don't have CFG, so it's impossible to
  get the number of instructions.

[llvmbot]

@llvm/pr-subscribers-bolt

Author: Amir Ayupov (aaupov)

Changes

---

Full diff: https://github.com/llvm/llvm-project/pull/101091.diff

2 Files Affected:

• (modified) bolt/include/bolt/Core/BinaryFunction.h (+6)
• (modified) bolt/lib/Core/BinaryFunction.cpp (+2)

diff --git a/bolt/include/bolt/Core/BinaryFunction.h b/bolt/include/bolt/Core/BinaryFunction.h
index 24c7db2f5d69c..2c8e23999b60c 100644
--- a/bolt/include/bolt/Core/BinaryFunction.h
+++ b/bolt/include/bolt/Core/BinaryFunction.h
@@ -242,6 +242,9 @@ class BinaryFunction {
   /// Original size of the function.
   uint64_t Size;
 
+  /// Original instruction count of the function, if disassembly succeeded.
+  uint64_t InputInstructionCount{0};
+
   /// Address of the function in output.
   uint64_t OutputAddress{0};
 
@@ -2173,6 +2176,9 @@ class BinaryFunction {
   /// Get the number of instructions within this function.
   uint64_t getInstructionCount() const;
 
+  /// Get the original number of instructions.
+  uint64_t getInputInstructionCount() const { return InputInstructionCount; }
+
   const CFIInstrMapType &getFDEProgram() const { return FrameInstructions; }
 
   void moveRememberRestorePair(BinaryBasicBlock *BB);
diff --git a/bolt/lib/Core/BinaryFunction.cpp b/bolt/lib/Core/BinaryFunction.cpp
index ea09371b57e8a..1f5869cd0ab73 100644
--- a/bolt/lib/Core/BinaryFunction.cpp
+++ b/bolt/lib/Core/BinaryFunction.cpp
@@ -1499,6 +1499,8 @@ Error BinaryFunction::disassemble() {
 
   clearList(Relocations);
 
+  InputInstructionCount = Instructions.size();
+
   if (!IsSimple) {
     clearList(Instructions);
     return createNonFatalBOLTError("");