1 //===- InlineSimple.cpp - Code to perform simple function inlining --------===//
3 // This file implements bottom-up inlining of functions into callees.
5 //===----------------------------------------------------------------------===//
8 #include "llvm/Function.h"
9 #include "llvm/iMemory.h"
10 #include "llvm/Support/CallSite.h"
11 #include "llvm/Transforms/IPO.h"
14 // FunctionInfo - For each function, calculate the size of it in blocks and
17 unsigned NumInsts, NumBlocks;
19 FunctionInfo() : NumInsts(0), NumBlocks(0) {}
22 class SimpleInliner : public Inliner {
23 std::map<const Function*, FunctionInfo> CachedFunctionInfo;
25 int getInlineCost(CallSite CS);
27 RegisterOpt<SimpleInliner> X("inline", "Function Integration/Inlining");
30 Pass *createFunctionInliningPass() { return new SimpleInliner(); }
32 // getInlineCost - The heuristic used to determine if we should inline the
33 // function call or not.
35 int SimpleInliner::getInlineCost(CallSite CS) {
36 Instruction *TheCall = CS.getInstruction();
37 const Function *Callee = CS.getCalledFunction();
38 const Function *Caller = TheCall->getParent()->getParent();
40 // Don't inline a directly recursive call.
41 if (Caller == Callee) return 2000000000;
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.
49 // If there is only one call of the function, and it has internal linkage,
50 // make it almost guaranteed to be inlined.
52 if (Callee->hasInternalLinkage() && Callee->hasOneUse())
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.
60 for (CallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end();
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.
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.
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.
77 else if (isa<Constant>(I) || isa<GlobalVariable>(I) || isa<AllocaInst>(I))
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];
85 // If we haven't calculated this information yet...
86 if (CalleeFI.NumBlocks == 0) {
87 unsigned NumInsts = 0, NumBlocks = 0;
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();
93 NumInsts += BB->size();
96 CalleeFI.NumBlocks = NumBlocks;
97 CalleeFI.NumInsts = NumInsts;
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;
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;