InlineSimple.cpp revision 6a67393e19632a9829c7ba0d3e7446db322612d9 
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/CommandLine.h"
14#include "Support/Debug.h"
15#include "Support/Statistic.h"
16#include <set>
17
18namespace {
19  Statistic<> NumInlined("inline", "Number of functions inlined");
20  Statistic<> NumDeleted("inline", "Number of functions deleted because all callers found");
21  cl::opt<unsigned>             // FIXME: 200 is VERY conservative
22  InlineLimit("inline-threshold", cl::Hidden, cl::init(200),
23              cl::desc("Control the amount of inlining to perform (default = 200)"));
24
25  struct FunctionInlining : public Pass {
26    virtual bool run(Module &M) {
27      bool Changed = false;
28      for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
29        Changed |= doInlining(I);
30      ProcessedFunctions.clear();
31      return Changed;
32    }
33
34  private:
35    std::set<Function*> ProcessedFunctions;  // Prevent infinite recursion
36    bool doInlining(Function *F);
37  };
38  RegisterOpt<FunctionInlining> X("inline", "Function Integration/Inlining");
39}
40
41Pass *createFunctionInliningPass() { return new FunctionInlining(); }
42
43
44// ShouldInlineFunction - The heuristic used to determine if we should inline
45// the function call or not.
46//
47static inline bool ShouldInlineFunction(const CallInst *CI) {
48  assert(CI->getParent() && CI->getParent()->getParent() &&
49	 "Call not embedded into a function!");
50
51  const Function *Callee = CI->getCalledFunction();
52  if (Callee == 0 || Callee->isExternal())
53    return false;  // Cannot inline an indirect call... or external function.
54
55  // Don't inline a recursive call.
56  const Function *Caller = CI->getParent()->getParent();
57  if (Caller == Callee) return false;
58
59  // InlineQuality - This value measures how good of an inline candidate this
60  // call site is to inline.  The initial value determines how aggressive the
61  // inliner is.  If this value is negative after the final computation,
62  // inlining is not performed.
63  //
64  int InlineQuality = InlineLimit;
65
66  // If there is only one call of the function, and it has internal linkage,
67  // make it almost guaranteed to be inlined.
68  //
69  if (Callee->use_size() == 1 && Callee->hasInternalLinkage())
70    InlineQuality += 30000;
71
72  // Add to the inline quality for properties that make the call valueable to
73  // inline.  This includes factors that indicate that the result of inlining
74  // the function will be optimizable.  Currently this just looks at arguments
75  // passed into the function.
76  //
77  for (User::const_op_iterator I = CI->op_begin()+1, E = CI->op_end();
78       I != E; ++I){
79    // Each argument passed in has a cost at both the caller and the callee
80    // sides.  This favors functions that take many arguments over functions
81    // that take few arguments.
82    InlineQuality += 20;
83
84    // If this is a function being passed in, it is very likely that we will be
85    // able to turn an indirect function call into a direct function call.
86    if (isa<Function>(I))
87      InlineQuality += 100;
88
89    // If a constant, global variable or alloca is passed in, inlining this
90    // function is likely to allow significant future optimization possibilities
91    // (constant propagation, scalar promotion, and scalarization), so encourage
92    // the inlining of the function.
93    //
94    else if (isa<Constant>(I) || isa<GlobalVariable>(I) || isa<AllocaInst>(I))
95      InlineQuality += 60;
96  }
97
98  // Now that we have considered all of the factors that make the call site more
99  // likely to be inlined, look at factors that make us not want to inline it.
100  // As soon as the inline quality gets negative, bail out.
101
102  // Look at the size of the callee.  Each basic block counts as 20 units, and
103  // each instruction counts as 10.
104  for (Function::const_iterator BB = Callee->begin(), E = Callee->end();
105       BB != E; ++BB) {
106    InlineQuality -= BB->size()*10 + 20;
107    if (InlineQuality < 0) return false;
108  }
109
110  // Don't inline into something too big, which would make it bigger.  Here, we
111  // count each basic block as a single unit.
112  for (Function::const_iterator BB = Caller->begin(), E = Caller->end();
113       BB != E; ++BB) {
114    --InlineQuality;
115    if (InlineQuality < 0) return false;
116  }
117
118  // If we get here, this call site is high enough "quality" to inline.
119  DEBUG(std::cerr << "Inlining in '" << Caller->getName()
120                  << "', quality = " << InlineQuality << ": " << *CI);
121  return true;
122}
123
124
125// doInlining - Use a heuristic based approach to inline functions that seem to
126// look good.
127//
128bool FunctionInlining::doInlining(Function *F) {
129  // If we have already processed this function (ie, it is recursive) don't
130  // revisit.
131  std::set<Function*>::iterator PFI = ProcessedFunctions.lower_bound(F);
132  if (PFI != ProcessedFunctions.end() && *PFI == F) return false;
133
134  // Insert the function in the set so it doesn't get revisited.
135  ProcessedFunctions.insert(PFI, F);
136
137  bool Changed = false;
138  for (Function::iterator BB = F->begin(); BB != F->end(); ++BB)
139    for (BasicBlock::iterator I = BB->begin(); I != BB->end(); ) {
140      bool ShouldInc = true;
141      // Found a call instruction? FIXME: This should also handle INVOKEs
142      if (CallInst *CI = dyn_cast<CallInst>(I)) {
143        if (Function *Callee = CI->getCalledFunction()) {
144          doInlining(Callee);  // Inline in callees before callers!
145
146          // Decide whether we should inline this function...
147          if (ShouldInlineFunction(CI)) {
148            // Save an iterator to the instruction before the call if it exists,
149            // otherwise get an iterator at the end of the block... because the
150            // call will be destroyed.
151            //
152            BasicBlock::iterator SI;
153            if (I != BB->begin()) {
154              SI = I; --SI;           // Instruction before the call...
155            } else {
156              SI = BB->end();
157            }
158
159            // Attempt to inline the function...
160            if (InlineFunction(CI)) {
161              ++NumInlined;
162              Changed = true;
163              // Move to instruction before the call...
164              I = (SI == BB->end()) ? BB->begin() : SI;
165              ShouldInc = false;  // Don't increment iterator until next time
166
167              // If we inlined the last possible call site to the function,
168              // delete the function body now.
169              if (Callee->use_empty() &&
170                  (Callee->hasInternalLinkage()||Callee->hasLinkOnceLinkage())){
171                F->getParent()->getFunctionList().erase(Callee);
172                ++NumDeleted;
173                if (Callee == F) return true;
174              }
175            }
176          }
177        }
178      }
179      if (ShouldInc) ++I;
180    }
181
182  return Changed;
183}
184
185