1 //===- InlineSimple.cpp - Code to perform simple function inlining --------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements bottom-up inlining of functions into callees.
12 //===----------------------------------------------------------------------===//
15 #include "llvm/Function.h"
16 #include "llvm/iMemory.h"
17 #include "llvm/Support/CallSite.h"
18 #include "llvm/Transforms/IPO.h"
23 // FunctionInfo - For each function, calculate the size of it in blocks and
26 unsigned NumInsts, NumBlocks;
28 FunctionInfo() : NumInsts(0), NumBlocks(0) {}
31 class SimpleInliner : public Inliner {
32 std::map<const Function*, FunctionInfo> CachedFunctionInfo;
34 int getInlineCost(CallSite CS);
36 RegisterOpt<SimpleInliner> X("inline", "Function Integration/Inlining");
39 Pass *createFunctionInliningPass() { return new SimpleInliner(); }
41 // getInlineCost - The heuristic used to determine if we should inline the
42 // function call or not.
44 int SimpleInliner::getInlineCost(CallSite CS) {
45 Instruction *TheCall = CS.getInstruction();
46 const Function *Callee = CS.getCalledFunction();
47 const Function *Caller = TheCall->getParent()->getParent();
49 // Don't inline a directly recursive call.
50 if (Caller == Callee) return 2000000000;
52 // InlineCost - This value measures how good of an inline candidate this call
53 // site is to inline. A lower inline cost make is more likely for the call to
54 // be inlined. This value may go negative.
58 // If there is only one call of the function, and it has internal linkage,
59 // make it almost guaranteed to be inlined.
61 if (Callee->hasInternalLinkage() && Callee->hasOneUse())
64 // Add to the inline quality for properties that make the call valuable to
65 // inline. This includes factors that indicate that the result of inlining
66 // the function will be optimizable. Currently this just looks at arguments
67 // passed into the function.
69 for (CallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end();
71 // Each argument passed in has a cost at both the caller and the callee
72 // sides. This favors functions that take many arguments over functions
73 // that take few arguments.
76 // If this is a function being passed in, it is very likely that we will be
77 // able to turn an indirect function call into a direct function call.
81 // If a constant, global variable or alloca is passed in, inlining this
82 // function is likely to allow significant future optimization possibilities
83 // (constant propagation, scalar promotion, and scalarization), so encourage
84 // the inlining of the function.
86 else if (isa<Constant>(I) || isa<GlobalVariable>(I) || isa<AllocaInst>(I))
90 // Now that we have considered all of the factors that make the call site more
91 // likely to be inlined, look at factors that make us not want to inline it.
92 FunctionInfo &CalleeFI = CachedFunctionInfo[Callee];
94 // If we haven't calculated this information yet...
95 if (CalleeFI.NumBlocks == 0) {
96 unsigned NumInsts = 0, NumBlocks = 0;
98 // Look at the size of the callee. Each basic block counts as 20 units, and
99 // each instruction counts as 10.
100 for (Function::const_iterator BB = Callee->begin(), E = Callee->end();
102 NumInsts += BB->size();
105 CalleeFI.NumBlocks = NumBlocks;
106 CalleeFI.NumInsts = NumInsts;
109 // Don't inline into something too big, which would make it bigger. Here, we
110 // count each basic block as a single unit.
111 InlineCost += Caller->size()*2;
114 // Look at the size of the callee. Each basic block counts as 20 units, and
115 // each instruction counts as 10.
116 InlineCost += CalleeFI.NumInsts*10 + CalleeFI.NumBlocks*20;
120 } // End llvm namespace