Implement InlineFunction to force inline at call site

src/backend/codegen/include/codegen/utils/codegen_utils.h

@@ -30,6 +30,7 @@
 #include "codegen/utils/macros.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/Twine.h"
+#include "llvm/Analysis/CallGraph.h"
 #include "llvm/ExecutionEngine/ExecutionEngine.h"
 #include "llvm/IR/BasicBlock.h"
 #include "llvm/IR/Constants.h"
@@ -43,6 +44,7 @@
 #include "llvm/IR/Type.h"
 #include "llvm/IR/Intrinsics.h"
 #include "llvm/IR/Value.h"
+#include "llvm/Transforms/Utils/Cloning.h"
 
 namespace gpcodegen {
 
@@ -479,6 +481,24 @@ class CodegenUtils {
   void CreateFallback(llvm::Function* regular_function,
                       llvm::Function* generated_function);
 
+  /*
+   * @brief Force inline an LLVM function at the call site. Note that this only
+   *        does one level of inlining.
+   *
+   * @param LLVM call Instruction where the called function should be inlined
+   * @return false if it is not possible to inline. true otherwise.
+   */
+  bool InlineFunction(llvm::CallInst* call_inst) {
+    // Check that the call instruction belongs to a BasicBlock which is part of
+    // a valid function
+    if (!(call_inst && call_inst->getParent()
+          && call_inst->getParent()->getParent())){
+      return false;
+    }
+    llvm::InlineFunctionInfo info;
+    return llvm::InlineFunction(llvm::CallSite(call_inst), info);
+  }
+
  private:
   // Give ClangCompiler access to 'context_' add allow it to add compiled C++
   // sources to 'auxiliary_modules_'.

src/backend/codegen/tests/codegen_utils_unittest.cc

@@ -41,6 +41,7 @@
 #include "llvm/IR/GlobalVariable.h"
 #include "llvm/IR/Instruction.h"
 #include "llvm/IR/Instructions.h"
+#include "llvm/IR/InstIterator.h"
 #include "llvm/IR/Module.h"
 #include "llvm/IR/Type.h"
 #include "llvm/IR/Value.h"
@@ -2736,9 +2737,9 @@ TEST_F(CodegenUtilsTest, CppClassObjectTest) {
   EXPECT_EQ(-12.75, (*accumulate_test_fn_compiled)(-22.75));
 }
 
-// Test GetOrGetOrRegisterExternalFunction to return the right llvm::Function if
+// Test GetOrRegisterExternalFunction to return the right llvm::Function if
 // previously registered or else register it anew
-TEST_F(CodegenUtilsTest, GetOrGetOrRegisterExternalFunctionTest) {
+TEST_F(CodegenUtilsTest, GetOrRegisterExternalFunctionTest) {
   // Test previous unregistered function
   EXPECT_EQ(nullptr, codegen_utils_->module()->getFunction("floor"));
   llvm::Function* floor_func = codegen_utils_->GetOrRegisterExternalFunction(
@@ -2762,6 +2763,56 @@ TEST_F(CodegenUtilsTest, GetOrGetOrRegisterExternalFunctionTest) {
   EXPECT_EQ(expected_fprintf_func, fprintf_func);
 }
 
+// Utility method to compute the number of calls in an llvm::Function*
+int GetLLVMFunctionCallCount(llvm::Function* F) {
+  return std::count_if(llvm::inst_begin(F), llvm::inst_end(F),
+      [] (llvm::Instruction& i)-> bool {
+            return (llvm::dyn_cast<llvm::CallInst>(&i));
+      });
+}
+
+// Test InlineFunction
+TEST_F(CodegenUtilsTest, InlineFunctionTest) {
+  auto irb = codegen_utils_->ir_builder();
+
+  typedef int (*AddConstToIntFn) (int);
+
+  // Create a simple adds 1 to a number and returns the new value
+  llvm::Function* add_one_fn = codegen_utils_->CreateFunction<AddConstToIntFn>("add_one");
+  irb->SetInsertPoint(codegen_utils_->CreateBasicBlock("main", add_one_fn));
+  irb->CreateRet(irb->CreateAdd(ArgumentByPosition(add_one_fn, 0),
+                                codegen_utils_->GetConstant(1)));
+
+  // Create another simple function add_two which calls add_one twice
+  llvm::Function* add_two_fn = codegen_utils_->CreateFunction<AddConstToIntFn>("add_two");
+  irb->SetInsertPoint(codegen_utils_->CreateBasicBlock("main", add_two_fn));
+  llvm::CallInst* first_call = irb->CreateCall(add_one_fn, {ArgumentByPosition(add_two_fn, 0)});
+  llvm::CallInst* second_call = irb->CreateCall(add_one_fn, {first_call});
+  irb->CreateRet(second_call);
+
+
+  EXPECT_EQ(GetLLVMFunctionCallCount(add_two_fn), 2);
+
+  EXPECT_TRUE(codegen_utils_->InlineFunction(first_call));
+  EXPECT_EQ(GetLLVMFunctionCallCount(add_two_fn), 1);
+
+  EXPECT_FALSE(codegen_utils_->InlineFunction(first_call));
+
+  EXPECT_TRUE(codegen_utils_->InlineFunction(second_call));
+  EXPECT_EQ(GetLLVMFunctionCallCount(add_two_fn), 0);
+
+  // Compiled module
+  EXPECT_TRUE(codegen_utils_->PrepareForExecution(
+      CodegenUtils::OptimizationLevel::kNone, false));
+  AddConstToIntFn compiled_add_two_fn =
+      codegen_utils_->GetFunctionPointer<AddConstToIntFn>("add_two");
+
+  // Test normal functionality, even after inlining
+  EXPECT_TRUE(nullptr != compiled_add_two_fn);
+  EXPECT_EQ(compiled_add_two_fn(5), 7);
+  EXPECT_EQ(compiled_add_two_fn(-5), -3);
+}
+
 
 #ifdef GPCODEGEN_DEBUG