src/llvm/lib/Transforms/IPO/InlineAlways.cpp

   1 //===- InlineAlways.cpp - Code to inline always_inline functions ----------===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file is distributed under the University of Illinois Open Source
   6 // License. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9 //
  10 // This file implements a custom inliner that handles only functions that
  11 // are marked as "always inline".
  12 //
  13 //===----------------------------------------------------------------------===//
  14
  15 #include "llvm/Transforms/IPO.h"
  16 #include "llvm/ADT/SmallPtrSet.h"
  17 #include "llvm/Analysis/AliasAnalysis.h"
  18 #include "llvm/Analysis/AssumptionCache.h"
  19 #include "llvm/Analysis/CallGraph.h"
  20 #include "llvm/Analysis/InlineCost.h"
  21 #include "llvm/IR/CallSite.h"
  22 #include "llvm/IR/CallingConv.h"
  23 #include "llvm/IR/DataLayout.h"
  24 #include "llvm/IR/Instructions.h"
  25 #include "llvm/IR/IntrinsicInst.h"
  26 #include "llvm/IR/Module.h"
  27 #include "llvm/IR/Type.h"
  28 #include "llvm/Transforms/IPO/InlinerPass.h"
  29
  30 using namespace llvm;
  31
  32 #define DEBUG_TYPE "inline"
  33
  34 namespace {
  35
  36 /// \brief Inliner pass which only handles "always inline" functions.
  37 class AlwaysInliner : public Inliner {
  38   InlineCostAnalysis *ICA;
  39
  40 public:
  41   // Use extremely low threshold.
  42   AlwaysInliner() : Inliner(ID, -2000000000, /*InsertLifetime*/ true),
  43                     ICA(nullptr) {
  44     initializeAlwaysInlinerPass(*PassRegistry::getPassRegistry());
  45   }
  46
  47   AlwaysInliner(bool InsertLifetime)
  48       : Inliner(ID, -2000000000, InsertLifetime), ICA(nullptr) {
  49     initializeAlwaysInlinerPass(*PassRegistry::getPassRegistry());
  50   }
  51
  52   static char ID; // Pass identification, replacement for typeid
  53
  54   InlineCost getInlineCost(CallSite CS) override;
  55
  56   void getAnalysisUsage(AnalysisUsage &AU) const override;
  57   bool runOnSCC(CallGraphSCC &SCC) override;
  58
  59   using llvm::Pass::doFinalization;
  60   bool doFinalization(CallGraph &CG) override {
  61     return removeDeadFunctions(CG, /*AlwaysInlineOnly=*/ true);
  62   }
  63 };
  64
  65 }
  66
  67 char AlwaysInliner::ID = 0;
  68 INITIALIZE_PASS_BEGIN(AlwaysInliner, "always-inline",
  69                 "Inliner for always_inline functions", false, false)
  70 INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
  71 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
  72 INITIALIZE_PASS_DEPENDENCY(CallGraphWrapperPass)
  73 INITIALIZE_PASS_DEPENDENCY(InlineCostAnalysis)
  74 INITIALIZE_PASS_END(AlwaysInliner, "always-inline",
  75                 "Inliner for always_inline functions", false, false)
  76
  77 Pass *llvm::createAlwaysInlinerPass() { return new AlwaysInliner(); }
  78
  79 Pass *llvm::createAlwaysInlinerPass(bool InsertLifetime) {
  80   return new AlwaysInliner(InsertLifetime);
  81 }
  82
  83 /// \brief Get the inline cost for the always-inliner.
  84 ///
  85 /// The always inliner *only* handles functions which are marked with the
  86 /// attribute to force inlining. As such, it is dramatically simpler and avoids
  87 /// using the powerful (but expensive) inline cost analysis. Instead it uses
  88 /// a very simple and boring direct walk of the instructions looking for
  89 /// impossible-to-inline constructs.
  90 ///
  91 /// Note, it would be possible to go to some lengths to cache the information
  92 /// computed here, but as we only expect to do this for relatively few and
  93 /// small functions which have the explicit attribute to force inlining, it is
  94 /// likely not worth it in practice.
  95 InlineCost AlwaysInliner::getInlineCost(CallSite CS) {
  96   Function *Callee = CS.getCalledFunction();
  97
  98   // Only inline direct calls to functions with always-inline attributes
  99   // that are viable for inlining. FIXME: We shouldn't even get here for
 100   // declarations.
 101   if (Callee && !Callee->isDeclaration() &&
 102       CS.hasFnAttr(Attribute::AlwaysInline) &&
 103       ICA->isInlineViable(*Callee))
 104     return InlineCost::getAlways();
 105
 106   return InlineCost::getNever();
 107 }
 108
 109 bool AlwaysInliner::runOnSCC(CallGraphSCC &SCC) {
 110   ICA = &getAnalysis<InlineCostAnalysis>();
 111   return Inliner::runOnSCC(SCC);
 112 }
 113
 114 void AlwaysInliner::getAnalysisUsage(AnalysisUsage &AU) const {
 115   AU.addRequired<InlineCostAnalysis>();
 116   Inliner::getAnalysisUsage(AU);
 117 }