InlineSimple.cpp revision bacc773d207700dede0701d08e15dfdc650678e9 
1//===- InlineSimple.cpp - Code to perform simple function inlining --------===//
2//
3// This file implements bottom-up inlining of functions into callees.
4//
5//===----------------------------------------------------------------------===//
6
7#include "Inliner.h"
8#include "llvm/Function.h"
9#include "llvm/iMemory.h"
10#include "llvm/Support/CallSite.h"
11#include "llvm/Transforms/IPO.h"
12
13namespace {
14  // FunctionInfo - For each function, calculate the size of it in blocks and
15  // instructions.
16  struct FunctionInfo {
17    unsigned NumInsts, NumBlocks;
18
19    FunctionInfo() : NumInsts(0), NumBlocks(0) {}
20  };
21
22  class SimpleInliner : public Inliner {
23    std::map<const Function*, FunctionInfo> CachedFunctionInfo;
24  public:
25    int getInlineCost(CallSite CS);
26  };
27  RegisterOpt<SimpleInliner> X("inline", "Function Integration/Inlining");
28}
29
30Pass *createFunctionInliningPass() { return new SimpleInliner(); }
31
32// getInlineCost - The heuristic used to determine if we should inline the
33// function call or not.
34//
35int SimpleInliner::getInlineCost(CallSite CS) {
36  Instruction *TheCall = CS.getInstruction();
37  const Function *Callee = CS.getCalledFunction();
38  const Function *Caller = TheCall->getParent()->getParent();
39
40  // Don't inline a directly recursive call.
41  if (Caller == Callee) return 2000000000;
42
43  // InlineCost - This value measures how good of an inline candidate this call
44  // site is to inline.  A lower inline cost make is more likely for the call to
45  // be inlined.  This value may go negative.
46  //
47  int InlineCost = 0;
48
49  // If there is only one call of the function, and it has internal linkage,
50  // make it almost guaranteed to be inlined.
51  //
52  if (Callee->hasInternalLinkage() && Callee->hasOneUse())
53    InlineCost -= 30000;
54
55  // Add to the inline quality for properties that make the call valuable to
56  // inline.  This includes factors that indicate that the result of inlining
57  // the function will be optimizable.  Currently this just looks at arguments
58  // passed into the function.
59  //
60  for (CallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end();
61       I != E; ++I) {
62    // Each argument passed in has a cost at both the caller and the callee
63    // sides.  This favors functions that take many arguments over functions
64    // that take few arguments.
65    InlineCost -= 20;
66
67    // If this is a function being passed in, it is very likely that we will be
68    // able to turn an indirect function call into a direct function call.
69    if (isa<Function>(I))
70      InlineCost -= 100;
71
72    // If a constant, global variable or alloca is passed in, inlining this
73    // function is likely to allow significant future optimization possibilities
74    // (constant propagation, scalar promotion, and scalarization), so encourage
75    // the inlining of the function.
76    //
77    else if (isa<Constant>(I) || isa<GlobalVariable>(I) || isa<AllocaInst>(I))
78      InlineCost -= 60;
79  }
80
81  // Now that we have considered all of the factors that make the call site more
82  // likely to be inlined, look at factors that make us not want to inline it.
83  FunctionInfo &CalleeFI = CachedFunctionInfo[Callee];
84
85  // If we haven't calculated this information yet...
86  if (CalleeFI.NumBlocks == 0) {
87    unsigned NumInsts = 0, NumBlocks = 0;
88
89    // Look at the size of the callee.  Each basic block counts as 20 units, and
90    // each instruction counts as 10.
91    for (Function::const_iterator BB = Callee->begin(), E = Callee->end();
92         BB != E; ++BB) {
93      NumInsts += BB->size();
94      NumBlocks++;
95    }
96    CalleeFI.NumBlocks = NumBlocks;
97    CalleeFI.NumInsts  = NumInsts;
98  }
99
100  // Don't inline into something too big, which would make it bigger.  Here, we
101  // count each basic block as a single unit.
102  InlineCost += Caller->size()*2;
103
104
105  // Look at the size of the callee.  Each basic block counts as 20 units, and
106  // each instruction counts as 10.
107  InlineCost += CalleeFI.NumInsts*10 + CalleeFI.NumBlocks*20;
108  return InlineCost;
109}
110