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"
21 // FunctionInfo - For each function, calculate the size of it in blocks and
24 unsigned NumInsts, NumBlocks;
26 FunctionInfo() : NumInsts(0), NumBlocks(0) {}
29 class SimpleInliner : public Inliner {
30 std::map<const Function*, FunctionInfo> CachedFunctionInfo;
32 int getInlineCost(CallSite CS);
34 RegisterOpt<SimpleInliner> X("inline", "Function Integration/Inlining");
37 Pass *createFunctionInliningPass() { return new SimpleInliner(); }
39 // getInlineCost - The heuristic used to determine if we should inline the
40 // function call or not.
42 int SimpleInliner::getInlineCost(CallSite CS) {
43 Instruction *TheCall = CS.getInstruction();
44 const Function *Callee = CS.getCalledFunction();
45 const Function *Caller = TheCall->getParent()->getParent();
47 // Don't inline a directly recursive call.
48 if (Caller == Callee) return 2000000000;
50 // InlineCost - This value measures how good of an inline candidate this call
51 // site is to inline. A lower inline cost make is more likely for the call to
52 // be inlined. This value may go negative.
56 // If there is only one call of the function, and it has internal linkage,
57 // make it almost guaranteed to be inlined.
59 if (Callee->hasInternalLinkage() && Callee->hasOneUse())
62 // Add to the inline quality for properties that make the call valuable to
63 // inline. This includes factors that indicate that the result of inlining
64 // the function will be optimizable. Currently this just looks at arguments
65 // passed into the function.
67 for (CallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end();
69 // Each argument passed in has a cost at both the caller and the callee
70 // sides. This favors functions that take many arguments over functions
71 // that take few arguments.
74 // If this is a function being passed in, it is very likely that we will be
75 // able to turn an indirect function call into a direct function call.
79 // If a constant, global variable or alloca is passed in, inlining this
80 // function is likely to allow significant future optimization possibilities
81 // (constant propagation, scalar promotion, and scalarization), so encourage
82 // the inlining of the function.
84 else if (isa<Constant>(I) || isa<GlobalVariable>(I) || isa<AllocaInst>(I))
88 // Now that we have considered all of the factors that make the call site more
89 // likely to be inlined, look at factors that make us not want to inline it.
90 FunctionInfo &CalleeFI = CachedFunctionInfo[Callee];
92 // If we haven't calculated this information yet...
93 if (CalleeFI.NumBlocks == 0) {
94 unsigned NumInsts = 0, NumBlocks = 0;
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();
100 NumInsts += BB->size();
103 CalleeFI.NumBlocks = NumBlocks;
104 CalleeFI.NumInsts = NumInsts;
107 // Don't inline into something too big, which would make it bigger. Here, we
108 // count each basic block as a single unit.
109 InlineCost += Caller->size()*2;
112 // Look at the size of the callee. Each basic block counts as 20 units, and
113 // each instruction counts as 10.
114 InlineCost += CalleeFI.NumInsts*10 + CalleeFI.NumBlocks*20;