LLVM API Documentation

InlineAlways.cpp
Go to the documentation of this file.
00001 //===- InlineAlways.cpp - Code to inline always_inline functions ----------===//
00002 //
00003 //                     The LLVM Compiler Infrastructure
00004 //
00005 // This file is distributed under the University of Illinois Open Source
00006 // License. See LICENSE.TXT for details.
00007 //
00008 //===----------------------------------------------------------------------===//
00009 //
00010 // This file implements a custom inliner that handles only functions that
00011 // are marked as "always inline".
00012 //
00013 //===----------------------------------------------------------------------===//
00014 
00015 #define DEBUG_TYPE "inline"
00016 #include "llvm/Transforms/IPO.h"
00017 #include "llvm/ADT/SmallPtrSet.h"
00018 #include "llvm/Analysis/CallGraph.h"
00019 #include "llvm/Analysis/InlineCost.h"
00020 #include "llvm/IR/CallSite.h"
00021 #include "llvm/IR/CallingConv.h"
00022 #include "llvm/IR/DataLayout.h"
00023 #include "llvm/IR/Instructions.h"
00024 #include "llvm/IR/IntrinsicInst.h"
00025 #include "llvm/IR/Module.h"
00026 #include "llvm/IR/Type.h"
00027 #include "llvm/Transforms/IPO/InlinerPass.h"
00028 
00029 using namespace llvm;
00030 
00031 namespace {
00032 
00033 /// \brief Inliner pass which only handles "always inline" functions.
00034 class AlwaysInliner : public Inliner {
00035   InlineCostAnalysis *ICA;
00036 
00037 public:
00038   // Use extremely low threshold.
00039   AlwaysInliner() : Inliner(ID, -2000000000, /*InsertLifetime*/ true), ICA(0) {
00040     initializeAlwaysInlinerPass(*PassRegistry::getPassRegistry());
00041   }
00042 
00043   AlwaysInliner(bool InsertLifetime)
00044       : Inliner(ID, -2000000000, InsertLifetime), ICA(0) {
00045     initializeAlwaysInlinerPass(*PassRegistry::getPassRegistry());
00046   }
00047 
00048   static char ID; // Pass identification, replacement for typeid
00049 
00050   InlineCost getInlineCost(CallSite CS) override;
00051 
00052   void getAnalysisUsage(AnalysisUsage &AU) const override;
00053   bool runOnSCC(CallGraphSCC &SCC) override;
00054 
00055   using llvm::Pass::doFinalization;
00056   bool doFinalization(CallGraph &CG) override {
00057     return removeDeadFunctions(CG, /*AlwaysInlineOnly=*/ true);
00058   }
00059 };
00060 
00061 }
00062 
00063 char AlwaysInliner::ID = 0;
00064 INITIALIZE_PASS_BEGIN(AlwaysInliner, "always-inline",
00065                 "Inliner for always_inline functions", false, false)
00066 INITIALIZE_PASS_DEPENDENCY(CallGraphWrapperPass)
00067 INITIALIZE_PASS_DEPENDENCY(InlineCostAnalysis)
00068 INITIALIZE_PASS_END(AlwaysInliner, "always-inline",
00069                 "Inliner for always_inline functions", false, false)
00070 
00071 Pass *llvm::createAlwaysInlinerPass() { return new AlwaysInliner(); }
00072 
00073 Pass *llvm::createAlwaysInlinerPass(bool InsertLifetime) {
00074   return new AlwaysInliner(InsertLifetime);
00075 }
00076 
00077 /// \brief Get the inline cost for the always-inliner.
00078 ///
00079 /// The always inliner *only* handles functions which are marked with the
00080 /// attribute to force inlining. As such, it is dramatically simpler and avoids
00081 /// using the powerful (but expensive) inline cost analysis. Instead it uses
00082 /// a very simple and boring direct walk of the instructions looking for
00083 /// impossible-to-inline constructs.
00084 ///
00085 /// Note, it would be possible to go to some lengths to cache the information
00086 /// computed here, but as we only expect to do this for relatively few and
00087 /// small functions which have the explicit attribute to force inlining, it is
00088 /// likely not worth it in practice.
00089 InlineCost AlwaysInliner::getInlineCost(CallSite CS) {
00090   Function *Callee = CS.getCalledFunction();
00091 
00092   // Only inline direct calls to functions with always-inline attributes
00093   // that are viable for inlining. FIXME: We shouldn't even get here for
00094   // declarations.
00095   if (Callee && !Callee->isDeclaration() &&
00096       Callee->getAttributes().hasAttribute(AttributeSet::FunctionIndex,
00097                                            Attribute::AlwaysInline) &&
00098       ICA->isInlineViable(*Callee))
00099     return InlineCost::getAlways();
00100 
00101   return InlineCost::getNever();
00102 }
00103 
00104 bool AlwaysInliner::runOnSCC(CallGraphSCC &SCC) {
00105   ICA = &getAnalysis<InlineCostAnalysis>();
00106   return Inliner::runOnSCC(SCC);
00107 }
00108 
00109 void AlwaysInliner::getAnalysisUsage(AnalysisUsage &AU) const {
00110   AU.addRequired<InlineCostAnalysis>();
00111   Inliner::getAnalysisUsage(AU);
00112 }