Chapter 4: IR optimization

src/ast/ast_codegen.cpp

@@ -138,6 +138,9 @@ FunctionAST::codegen()
         // Validate the generated code, checking for consistency
         llvm::verifyFunction(*TheFunction);
 
+        // Optimize the function
+        TheFPM->run(*TheFunction);
+
         return TheFunction;
     }
 

src/kaleidoscope.cpp

@@ -22,6 +22,32 @@ InitializeModule()
     Builder = std::make_unique<llvm::IRBuilder<>>(*TheContext);
 }
 
+internal void 
+InitializePassManager()
+{
+    // Create a new pass manager attached to it.
+    TheFPM = std::make_unique<llvml::FunctionPassManager>(TheModule.get());
+
+    // Do simple "peephole" and bit-twiddling optimizations.
+    TheFPM->add(llvm::createInstructionCombiningPass());
+    // Reassociate expressions
+    TheFPM->add(llvm::createReassociatePass());
+    // Eliminate Common SubExpressions
+    TheFPM->add(llvm::createGVNPass());
+    // Simplify the control flow graph (deleting unreachable blocks, etc.)
+    TheFPM->add(llvm::createCFGSimplificationPass());
+
+    TheFPM->doInitialization();
+    // TODO(srp): See https://llvm.org/docs/Passes.html
+}
+
+internal void
+InitializeLLVM()
+{
+    InitializeModule();
+    InitializePassManager();
+}
+
 internal void
 HandleDefinition()
 {

src/linux_kaleidoscope.cpp

@@ -23,7 +23,7 @@ int main()
     getNextToken();
 
     // Make the module, which holds all the code.
-    InitializeModule();
+    InitializeLLVM();
 
     // Run the main "interpreter loop" now
     MainLoop();

src/platform/llvm/linux_llvm_include.hpp

@@ -13,3 +13,10 @@
 #include "llvm/IR/Module.h"
 #include "llvm/IR/Type.h"
 #include "llvm/IR/Verifier.h"
+
+#include "llvm/Pass.h"
+#include "llvm/IR/LegacyPassManager.h"
+#include "llvm/Transforms/InstCombine/InstCombine.h"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Transforms/Scalar/GVN.h"
+

src/platform/llvm/llvm_include.hpp

@@ -11,7 +11,10 @@
 #include <map>
 #include <string>
 
+namespace llvml = llvm::legacy;
+
 global_variable std::unique_ptr<llvm::LLVMContext> TheContext;
 global_variable std::unique_ptr<llvm::Module> TheModule;
 global_variable std::unique_ptr<llvm::IRBuilder<>> Builder;
 global_variable std::map<std::string, llvm::Value*> NamedValues;
+global_variable std::unique_ptr<llvml::FunctionPassManager> TheFPM;