LLVM API Documentation

InlineAlways.cpp
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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 #include "llvm/Transforms/IPO.h"
00016 #include "llvm/ADT/SmallPtrSet.h"
00017 #include "llvm/Analysis/AliasAnalysis.h"
00018 #include "llvm/Analysis/AssumptionCache.h"
00019 #include "llvm/Analysis/CallGraph.h"
00020 #include "llvm/Analysis/InlineCost.h"
00021 #include "llvm/IR/CallSite.h"
00022 #include "llvm/IR/CallingConv.h"
00023 #include "llvm/IR/DataLayout.h"
00024 #include "llvm/IR/Instructions.h"
00025 #include "llvm/IR/IntrinsicInst.h"
00026 #include "llvm/IR/Module.h"
00027 #include "llvm/IR/Type.h"
00028 #include "llvm/Transforms/IPO/InlinerPass.h"
00029 
00030 using namespace llvm;
00031 
00032 #define DEBUG_TYPE "inline"
00033 
00034 namespace {
00035 
00036 /// \brief Inliner pass which only handles "always inline" functions.
00037 class AlwaysInliner : public Inliner {
00038   InlineCostAnalysis *ICA;
00039 
00040 public:
00041   // Use extremely low threshold.
00042   AlwaysInliner() : Inliner(ID, -2000000000, /*InsertLifetime*/ true),
00043                     ICA(nullptr) {
00044     initializeAlwaysInlinerPass(*PassRegistry::getPassRegistry());
00045   }
00046 
00047   AlwaysInliner(bool InsertLifetime)
00048       : Inliner(ID, -2000000000, InsertLifetime), ICA(nullptr) {
00049     initializeAlwaysInlinerPass(*PassRegistry::getPassRegistry());
00050   }
00051 
00052   static char ID; // Pass identification, replacement for typeid
00053 
00054   InlineCost getInlineCost(CallSite CS) override;
00055 
00056   void getAnalysisUsage(AnalysisUsage &AU) const override;
00057   bool runOnSCC(CallGraphSCC &SCC) override;
00058 
00059   using llvm::Pass::doFinalization;
00060   bool doFinalization(CallGraph &CG) override {
00061     return removeDeadFunctions(CG, /*AlwaysInlineOnly=*/ true);
00062   }
00063 };
00064 
00065 }
00066 
00067 char AlwaysInliner::ID = 0;
00068 INITIALIZE_PASS_BEGIN(AlwaysInliner, "always-inline",
00069                 "Inliner for always_inline functions", false, false)
00070 INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
00071 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
00072 INITIALIZE_PASS_DEPENDENCY(CallGraphWrapperPass)
00073 INITIALIZE_PASS_DEPENDENCY(InlineCostAnalysis)
00074 INITIALIZE_PASS_END(AlwaysInliner, "always-inline",
00075                 "Inliner for always_inline functions", false, false)
00076 
00077 Pass *llvm::createAlwaysInlinerPass() { return new AlwaysInliner(); }
00078 
00079 Pass *llvm::createAlwaysInlinerPass(bool InsertLifetime) {
00080   return new AlwaysInliner(InsertLifetime);
00081 }
00082 
00083 /// \brief Get the inline cost for the always-inliner.
00084 ///
00085 /// The always inliner *only* handles functions which are marked with the
00086 /// attribute to force inlining. As such, it is dramatically simpler and avoids
00087 /// using the powerful (but expensive) inline cost analysis. Instead it uses
00088 /// a very simple and boring direct walk of the instructions looking for
00089 /// impossible-to-inline constructs.
00090 ///
00091 /// Note, it would be possible to go to some lengths to cache the information
00092 /// computed here, but as we only expect to do this for relatively few and
00093 /// small functions which have the explicit attribute to force inlining, it is
00094 /// likely not worth it in practice.
00095 InlineCost AlwaysInliner::getInlineCost(CallSite CS) {
00096   Function *Callee = CS.getCalledFunction();
00097 
00098   // Only inline direct calls to functions with always-inline attributes
00099   // that are viable for inlining. FIXME: We shouldn't even get here for
00100   // declarations.
00101   if (Callee && !Callee->isDeclaration() &&
00102       CS.hasFnAttr(Attribute::AlwaysInline) &&
00103       ICA->isInlineViable(*Callee))
00104     return InlineCost::getAlways();
00105 
00106   return InlineCost::getNever();
00107 }
00108 
00109 bool AlwaysInliner::runOnSCC(CallGraphSCC &SCC) {
00110   ICA = &getAnalysis<InlineCostAnalysis>();
00111   return Inliner::runOnSCC(SCC);
00112 }
00113 
00114 void AlwaysInliner::getAnalysisUsage(AnalysisUsage &AU) const {
00115   AU.addRequired<InlineCostAnalysis>();
00116   Inliner::getAnalysisUsage(AU);
00117 }