1 //===- FunctionInlining.cpp - Code to perform function inlining -----------===//
3 // This file implements bottom-up inlining of functions into callees.
5 //===----------------------------------------------------------------------===//
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/Statistic.h"
14 #include "Support/CommandLine.h"
18 Statistic<> NumInlined("inline", "Number of functions inlined");
19 cl::opt<unsigned> // FIXME: 200 is VERY conservative
20 InlineLimit("inline-threshold", cl::Hidden, cl::init(200),
21 cl::desc("Control the amount of inlining to perform (default = 200)"));
23 struct FunctionInlining : public Pass {
24 virtual bool run(Module &M) {
26 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
27 Changed |= doInlining(I);
28 ProcessedFunctions.clear();
33 std::set<Function*> ProcessedFunctions; // Prevent infinite recursion
34 bool doInlining(Function *F);
36 RegisterOpt<FunctionInlining> X("inline", "Function Integration/Inlining");
39 Pass *createFunctionInliningPass() { return new FunctionInlining(); }
42 // ShouldInlineFunction - The heuristic used to determine if we should inline
43 // the function call or not.
45 static inline bool ShouldInlineFunction(const CallInst *CI) {
46 assert(CI->getParent() && CI->getParent()->getParent() &&
47 "Call not embedded into a function!");
49 const Function *Callee = CI->getCalledFunction();
50 if (Callee == 0 || Callee->isExternal())
51 return false; // Cannot inline an indirect call... or external function.
53 // Don't inline a recursive call.
54 const Function *Caller = CI->getParent()->getParent();
55 if (Caller == Callee) return false;
57 // InlineQuality - This value measures how good of an inline candidate this
58 // call site is to inline. The initial value determines how aggressive the
59 // inliner is. If this value is negative after the final computation,
60 // inlining is not performed.
62 int InlineQuality = InlineLimit;
64 // If there is only one call of the function, and it has internal linkage,
65 // make it almost guaranteed to be inlined.
67 if (Callee->use_size() == 1 && Callee->hasInternalLinkage())
68 InlineQuality += 30000;
70 // Add to the inline quality for properties that make the call valueable to
71 // inline. This includes factors that indicate that the result of inlining
72 // the function will be optimizable. Currently this just looks at arguments
73 // passed into the function.
75 for (User::const_op_iterator I = CI->op_begin()+1, E = CI->op_end();
77 // Each argument passed in has a cost at both the caller and the callee
78 // sides. This favors functions that take many arguments over functions
79 // that take few arguments.
82 // If this is a function being passed in, it is very likely that we will be
83 // able to turn an indirect function call into a direct function call.
87 // If a constant, global variable or alloca is passed in, inlining this
88 // function is likely to allow significant future optimization possibilities
89 // (constant propagation, scalar promotion, and scalarization), so encourage
90 // the inlining of the function.
92 else if (isa<Constant>(I) || isa<GlobalVariable>(I) || isa<AllocaInst>(I))
96 // Now that we have considered all of the factors that make the call site more
97 // likely to be inlined, look at factors that make us not want to inline it.
98 // As soon as the inline quality gets negative, bail out.
100 // Look at the size of the callee. Each basic block counts as 20 units, and
101 // each instruction counts as 10.
102 for (Function::const_iterator BB = Callee->begin(), E = Callee->end();
104 InlineQuality -= BB->size()*10 + 20;
105 if (InlineQuality < 0) return false;
108 // Don't inline into something too big, which would make it bigger. Here, we
109 // count each basic block as a single unit.
110 for (Function::const_iterator BB = Caller->begin(), E = Caller->end();
113 if (InlineQuality < 0) return false;
116 // If we get here, this call site is high enough "quality" to inline.
117 DEBUG(std::cerr << "Inlining in '" << Caller->getName()
118 << "', quality = " << InlineQuality << ": " << *CI);
123 // doInlining - Use a heuristic based approach to inline functions that seem to
126 bool FunctionInlining::doInlining(Function *F) {
127 // If we have already processed this function (ie, it is recursive) don't
129 std::set<Function*>::iterator PFI = ProcessedFunctions.lower_bound(F);
130 if (PFI != ProcessedFunctions.end() && *PFI == F) return false;
132 // Insert the function in the set so it doesn't get revisited.
133 ProcessedFunctions.insert(PFI, F);
135 bool Changed = false;
136 for (Function::iterator BB = F->begin(); BB != F->end(); ++BB)
137 for (BasicBlock::iterator I = BB->begin(); I != BB->end(); ) {
138 bool ShouldInc = true;
139 // Found a call instruction? FIXME: This should also handle INVOKEs
140 if (CallInst *CI = dyn_cast<CallInst>(I)) {
141 if (Function *Callee = CI->getCalledFunction())
142 doInlining(Callee); // Inline in callees before callers!
144 // Decide whether we should inline this function...
145 if (ShouldInlineFunction(CI)) {
146 // Save an iterator to the instruction before the call if it exists,
147 // otherwise get an iterator at the end of the block... because the
148 // call will be destroyed.
150 BasicBlock::iterator SI;
151 if (I != BB->begin()) {
152 SI = I; --SI; // Instruction before the call...
157 // Attempt to inline the function...
158 if (InlineFunction(CI)) {
161 // Move to instruction before the call...
162 I = (SI == BB->end()) ? BB->begin() : SI;
163 ShouldInc = false; // Don't increment iterator until next time