From baad1a4b2346c1660af1e5d96449835d4abf4c47 Mon Sep 17 00:00:00 2001
From: Connor McLaughlin <stenzek@gmail.com>
Date: Tue, 25 May 2021 20:01:56 +1000
Subject: [PATCH] CPU/Recompiler: Optimize away nops completely

35% performance improvement for PGXP CPU mode in Racing Lagoon.
---
 src/core/cpu_recompiler_code_generator.cpp | 7 +++++++
 src/core/cpu_recompiler_code_generator.h   | 1 +
 src/core/cpu_types.cpp                     | 6 ++++++
 src/core/cpu_types.h                       | 1 +
 4 files changed, 15 insertions(+)

diff --git a/src/core/cpu_recompiler_code_generator.cpp b/src/core/cpu_recompiler_code_generator.cpp
index 363fb87f7..ee0832a04 100644
--- a/src/core/cpu_recompiler_code_generator.cpp
+++ b/src/core/cpu_recompiler_code_generator.cpp
@@ -65,6 +65,13 @@ bool CodeGenerator::CompileBlock(CodeBlock* block, CodeBlock::HostCodePointer* o
 
 bool CodeGenerator::CompileInstruction(const CodeBlockInstruction& cbi)
 {
+  if (IsNopInstruction(cbi.instruction))
+  {
+    InstructionPrologue(cbi, 1);
+    InstructionEpilogue(cbi);
+    return true;
+  }
+
   bool result;
   switch (cbi.instruction.op)
   {
diff --git a/src/core/cpu_recompiler_code_generator.h b/src/core/cpu_recompiler_code_generator.h
index 8d6210ee3..5550cfee1 100644
--- a/src/core/cpu_recompiler_code_generator.h
+++ b/src/core/cpu_recompiler_code_generator.h
@@ -214,6 +214,7 @@ private:
   //////////////////////////////////////////////////////////////////////////
   bool CompileInstruction(const CodeBlockInstruction& cbi);
   bool Compile_Fallback(const CodeBlockInstruction& cbi);
+  bool Compile_Nop(const CodeBlockInstruction& cbi);
   bool Compile_Bitwise(const CodeBlockInstruction& cbi);
   bool Compile_Shift(const CodeBlockInstruction& cbi);
   bool Compile_Load(const CodeBlockInstruction& cbi);
diff --git a/src/core/cpu_types.cpp b/src/core/cpu_types.cpp
index db9960e45..aa0cc548f 100644
--- a/src/core/cpu_types.cpp
+++ b/src/core/cpu_types.cpp
@@ -13,6 +13,12 @@ const char* GetRegName(Reg reg)
   return s_reg_names[static_cast<u8>(reg)];
 }
 
+bool IsNopInstruction(const Instruction& instruction)
+{
+  // TODO: Handle other types of nop.
+  return (instruction.bits == 0);
+}
+
 bool IsBranchInstruction(const Instruction& instruction)
 {
   switch (instruction.op)
diff --git a/src/core/cpu_types.h b/src/core/cpu_types.h
index 1f805c49a..5e840e4a3 100644
--- a/src/core/cpu_types.h
+++ b/src/core/cpu_types.h
@@ -220,6 +220,7 @@ union Instruction
 };
 
 // Instruction helpers.
+bool IsNopInstruction(const Instruction& instruction);
 bool IsBranchInstruction(const Instruction& instruction);
 bool IsUnconditionalBranchInstruction(const Instruction& instruction);
 bool IsDirectBranchInstruction(const Instruction& instruction);