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      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 }
    118