lib/Transforms/IPO/AlwaysInliner.cpp

   1 //===- InlineAlways.cpp - Code to inline always_inline functions ----------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This file implements a custom inliner that handles only functions that
  10 // are marked as "always inline".
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "llvm/Transforms/IPO/AlwaysInliner.h"
  15 #include "llvm/ADT/SetVector.h"
  16 #include "llvm/Analysis/AssumptionCache.h"
  17 #include "llvm/Analysis/InlineCost.h"
  18 #include "llvm/Analysis/TargetLibraryInfo.h"
  19 #include "llvm/IR/CallSite.h"
  20 #include "llvm/IR/CallingConv.h"
  21 #include "llvm/IR/DataLayout.h"
  22 #include "llvm/IR/Instructions.h"
  23 #include "llvm/IR/Module.h"
  24 #include "llvm/IR/Type.h"
  25 #include "llvm/Transforms/IPO.h"
  26 #include "llvm/Transforms/IPO/Inliner.h"
  27 #include "llvm/Transforms/Utils/Cloning.h"
  28 #include "llvm/Transforms/Utils/ModuleUtils.h"
  29
  30 using namespace llvm;
  31
  32 #define DEBUG_TYPE "inline"
  33
  34 PreservedAnalyses AlwaysInlinerPass::run(Module &M,
  35                                          ModuleAnalysisManager &MAM) {
  36   // Add inline assumptions during code generation.
  37   FunctionAnalysisManager &FAM =
  38       MAM.getResult<FunctionAnalysisManagerModuleProxy>(M).getManager();
  39   std::function<AssumptionCache &(Function &)> GetAssumptionCache =
  40       [&](Function &F) -> AssumptionCache & {
  41     return FAM.getResult<AssumptionAnalysis>(F);
  42   };
  43   InlineFunctionInfo IFI(/*cg=*/nullptr, &GetAssumptionCache);
  44
  45   SmallSetVector<CallSite, 16> Calls;
  46   bool Changed = false;
  47   SmallVector<Function *, 16> InlinedFunctions;
  48   for (Function &F : M)
  49     if (!F.isDeclaration() && F.hasFnAttribute(Attribute::AlwaysInline) &&
  50         isInlineViable(F)) {
  51       Calls.clear();
  52
  53       for (User *U : F.users())
  54         if (auto CS = CallSite(U))
  55           if (CS.getCalledFunction() == &F)
  56             Calls.insert(CS);
  57
  58       for (CallSite CS : Calls)
  59         // FIXME: We really shouldn't be able to fail to inline at this point!
  60         // We should do something to log or check the inline failures here.
  61         Changed |=
  62             InlineFunction(CS, IFI, /*CalleeAAR=*/nullptr, InsertLifetime);
  63
  64       // Remember to try and delete this function afterward. This both avoids
  65       // re-walking the rest of the module and avoids dealing with any iterator
  66       // invalidation issues while deleting functions.
  67       InlinedFunctions.push_back(&F);
  68     }
  69
  70   // Remove any live functions.
  71   erase_if(InlinedFunctions, [&](Function *F) {
  72     F->removeDeadConstantUsers();
  73     return !F->isDefTriviallyDead();
  74   });
  75
  76   // Delete the non-comdat ones from the module and also from our vector.
  77   auto NonComdatBegin = partition(
  78       InlinedFunctions, [&](Function *F) { return F->hasComdat(); });
  79   for (Function *F : make_range(NonComdatBegin, InlinedFunctions.end()))
  80     M.getFunctionList().erase(F);
  81   InlinedFunctions.erase(NonComdatBegin, InlinedFunctions.end());
  82
  83   if (!InlinedFunctions.empty()) {
  84     // Now we just have the comdat functions. Filter out the ones whose comdats
  85     // are not actually dead.
  86     filterDeadComdatFunctions(M, InlinedFunctions);
  87     // The remaining functions are actually dead.
  88     for (Function *F : InlinedFunctions)
  89       M.getFunctionList().erase(F);
  90   }
  91
  92   return Changed ? PreservedAnalyses::none() : PreservedAnalyses::all();
  93 }
  94
  95 namespace {
  96
  97 /// Inliner pass which only handles "always inline" functions.
  98 ///
  99 /// Unlike the \c AlwaysInlinerPass, this uses the more heavyweight \c Inliner
 100 /// base class to provide several facilities such as array alloca merging.
 101 class AlwaysInlinerLegacyPass : public LegacyInlinerBase {
 102
 103 public:
 104   AlwaysInlinerLegacyPass() : LegacyInlinerBase(ID, /*InsertLifetime*/ true) {
 105     initializeAlwaysInlinerLegacyPassPass(*PassRegistry::getPassRegistry());
 106   }
 107
 108   AlwaysInlinerLegacyPass(bool InsertLifetime)
 109       : LegacyInlinerBase(ID, InsertLifetime) {
 110     initializeAlwaysInlinerLegacyPassPass(*PassRegistry::getPassRegistry());
 111   }
 112
 113   /// Main run interface method.  We override here to avoid calling skipSCC().
 114   bool runOnSCC(CallGraphSCC &SCC) override { return inlineCalls(SCC); }
 115
 116   static char ID; // Pass identification, replacement for typeid
 117
 118   InlineCost getInlineCost(CallSite CS) override;
 119
 120   using llvm::Pass::doFinalization;
 121   bool doFinalization(CallGraph &CG) override {
 122     return removeDeadFunctions(CG, /*AlwaysInlineOnly=*/true);
 123   }
 124 };
 125 }
 126
 127 char AlwaysInlinerLegacyPass::ID = 0;
 128 INITIALIZE_PASS_BEGIN(AlwaysInlinerLegacyPass, "always-inline",
 129                       "Inliner for always_inline functions", false, false)
 130 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
 131 INITIALIZE_PASS_DEPENDENCY(CallGraphWrapperPass)
 132 INITIALIZE_PASS_DEPENDENCY(ProfileSummaryInfoWrapperPass)
 133 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
 134 INITIALIZE_PASS_END(AlwaysInlinerLegacyPass, "always-inline",
 135                     "Inliner for always_inline functions", false, false)
 136
 137 Pass *llvm::createAlwaysInlinerLegacyPass(bool InsertLifetime) {
 138   return new AlwaysInlinerLegacyPass(InsertLifetime);
 139 }
 140
 141 /// Get the inline cost for the always-inliner.
 142 ///
 143 /// The always inliner *only* handles functions which are marked with the
 144 /// attribute to force inlining. As such, it is dramatically simpler and avoids
 145 /// using the powerful (but expensive) inline cost analysis. Instead it uses
 146 /// a very simple and boring direct walk of the instructions looking for
 147 /// impossible-to-inline constructs.
 148 ///
 149 /// Note, it would be possible to go to some lengths to cache the information
 150 /// computed here, but as we only expect to do this for relatively few and
 151 /// small functions which have the explicit attribute to force inlining, it is
 152 /// likely not worth it in practice.
 153 InlineCost AlwaysInlinerLegacyPass::getInlineCost(CallSite CS) {
 154   Function *Callee = CS.getCalledFunction();
 155
 156   // Only inline direct calls to functions with always-inline attributes
 157   // that are viable for inlining.
 158   if (!Callee)
 159     return InlineCost::getNever("indirect call");
 160
 161   // FIXME: We shouldn't even get here for declarations.
 162   if (Callee->isDeclaration())
 163     return InlineCost::getNever("no definition");
 164
 165   if (!CS.hasFnAttr(Attribute::AlwaysInline))
 166     return InlineCost::getNever("no alwaysinline attribute");
 167
 168   auto IsViable = isInlineViable(*Callee);
 169   if (!IsViable)
 170     return InlineCost::getNever(IsViable.message);
 171
 172   return InlineCost::getAlways("always inliner");
 173 }