InlineSimple.cpp revision ca398dc3989d35e8516489fd163e012133bd41cb 
1//===- FunctionInlining.cpp - Code to perform function inlining -----------===//
2//
3// This file implements bottom-up inlining of functions into callees.
4//
5//===----------------------------------------------------------------------===//
6
7#include "llvm/Transforms/IPO.h"
8#include "llvm/Transforms/Utils/Cloning.h"
9#include "llvm/Module.h"
10#include "llvm/Pass.h"
11#include "llvm/iOther.h"
12#include "llvm/iMemory.h"
13#include "Support/Statistic.h"
14#include <set>
15
16namespace {
17  Statistic<> NumInlined("inline", "Number of functions inlined");
18
19  struct FunctionInlining : public Pass {
20    virtual bool run(Module &M) {
21      bool Changed = false;
22      for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
23        Changed |= doInlining(I);
24      ProcessedFunctions.clear();
25      return Changed;
26    }
27
28  private:
29    std::set<Function*> ProcessedFunctions;  // Prevent infinite recursion
30    bool doInlining(Function *F);
31  };
32  RegisterOpt<FunctionInlining> X("inline", "Function Integration/Inlining");
33}
34
35Pass *createFunctionInliningPass() { return new FunctionInlining(); }
36
37
38// ShouldInlineFunction - The heuristic used to determine if we should inline
39// the function call or not.
40//
41static inline bool ShouldInlineFunction(const CallInst *CI) {
42  assert(CI->getParent() && CI->getParent()->getParent() &&
43	 "Call not embedded into a function!");
44
45  const Function *Callee = CI->getCalledFunction();
46  if (Callee == 0 || Callee->isExternal())
47    return false;  // Cannot inline an indirect call... or external function.
48
49  // Don't inline a recursive call.
50  const Function *Caller = CI->getParent()->getParent();
51  if (Caller == Callee) return false;
52
53  // InlineQuality - This value measures how good of an inline candidate this
54  // call site is to inline.  The initial value determines how aggressive the
55  // inliner is.  If this value is negative after the final computation,
56  // inlining is not performed.
57  //
58  int InlineQuality = 200;            // FIXME: This is VERY conservative
59
60  // If there is only one call of the function, and it has internal linkage,
61  // make it almost guaranteed to be inlined.
62  //
63  if (Callee->use_size() == 1 && Callee->hasInternalLinkage())
64    InlineQuality += 30000;
65
66  // Add to the inline quality for properties that make the call valueable to
67  // inline.  This includes factors that indicate that the result of inlining
68  // the function will be optimizable.  Currently this just looks at arguments
69  // passed into the function.
70  //
71  for (User::const_op_iterator I = CI->op_begin()+1, E = CI->op_end();
72       I != E; ++I){
73    // Each argument passed in has a cost at both the caller and the callee
74    // sides.  This favors functions that take many arguments over functions
75    // that take few arguments.
76    InlineQuality += 20;
77
78    // If this is a function being passed in, it is very likely that we will be
79    // able to turn an indirect function call into a direct function call.
80    if (isa<Function>(I))
81      InlineQuality += 100;
82
83    // If a constant, global variable or alloca is passed in, inlining this
84    // function is likely to allow significant future optimization possibilities
85    // (constant propagation, scalar promotion, and scalarization), so encourage
86    // the inlining of the function.
87    //
88    else if (isa<Constant>(I) || isa<GlobalVariable>(I) || isa<AllocaInst>(I))
89      InlineQuality += 60;
90  }
91
92  // Now that we have considered all of the factors that make the call site more
93  // likely to be inlined, look at factors that make us not want to inline it.
94  // As soon as the inline quality gets negative, bail out.
95
96  // Look at the size of the callee.  Each basic block counts as 20 units, and
97  // each instruction counts as 10.
98  for (Function::const_iterator BB = Callee->begin(), E = Callee->end();
99       BB != E; ++BB) {
100    InlineQuality -= BB->size()*10 + 20;
101    if (InlineQuality < 0) return false;
102  }
103
104  // Don't inline into something too big, which would make it bigger.  Here, we
105  // count each basic block as a single unit.
106  for (Function::const_iterator BB = Caller->begin(), E = Caller->end();
107       BB != E; ++BB) {
108    --InlineQuality;
109    if (InlineQuality < 0) return false;
110  }
111
112  // If we get here, this call site is high enough "quality" to inline.
113  DEBUG(std::cerr << "Inlining in '" << Caller->getName()
114                  << "', quality = " << InlineQuality << ": " << *CI);
115  return true;
116}
117
118
119// doInlining - Use a heuristic based approach to inline functions that seem to
120// look good.
121//
122bool FunctionInlining::doInlining(Function *F) {
123  // If we have already processed this function (ie, it is recursive) don't
124  // revisit.
125  std::set<Function*>::iterator PFI = ProcessedFunctions.lower_bound(F);
126  if (PFI != ProcessedFunctions.end() && *PFI == F) return false;
127
128  // Insert the function in the set so it doesn't get revisited.
129  ProcessedFunctions.insert(PFI, F);
130
131  bool Changed = false;
132  for (Function::iterator BB = F->begin(); BB != F->end(); ++BB)
133    for (BasicBlock::iterator I = BB->begin(); I != BB->end(); ) {
134      bool ShouldInc = true;
135      // Found a call instruction? FIXME: This should also handle INVOKEs
136      if (CallInst *CI = dyn_cast<CallInst>(I)) {
137        if (Function *Callee = CI->getCalledFunction())
138          doInlining(Callee);  // Inline in callees before callers!
139
140        // Decide whether we should inline this function...
141        if (ShouldInlineFunction(CI)) {
142          // Save an iterator to the instruction before the call if it exists,
143          // otherwise get an iterator at the end of the block... because the
144          // call will be destroyed.
145          //
146          BasicBlock::iterator SI;
147          if (I != BB->begin()) {
148            SI = I; --SI;           // Instruction before the call...
149          } else {
150            SI = BB->end();
151          }
152
153          // Attempt to inline the function...
154          if (InlineFunction(CI)) {
155            ++NumInlined;
156            Changed = true;
157            // Move to instruction before the call...
158            I = (SI == BB->end()) ? BB->begin() : SI;
159            ShouldInc = false;  // Don't increment iterator until next time
160          }
161        }
162      }
163      if (ShouldInc) ++I;
164    }
165
166  return Changed;
167}
168
169