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 struct SimpleInliner : public Inliner {
15 int getInlineCost(CallSite CS);
17 RegisterOpt<SimpleInliner> X("inline", "Function Integration/Inlining");
20 Pass *createFunctionInliningPass() { return new SimpleInliner(); }
23 // getInlineCost - The heuristic used to determine if we should inline the
24 // function call or not.
26 int SimpleInliner::getInlineCost(CallSite CS) {
27 Instruction *TheCall = CS.getInstruction();
28 const Function *Callee = CS.getCalledFunction();
29 const Function *Caller = TheCall->getParent()->getParent();
31 // Don't inline a directly recursive call.
32 if (Caller == Callee) return 2000000000;
34 // InlineCost - This value measures how good of an inline candidate this call
35 // site is to inline. A lower inline cost make is more likely for the call to
36 // be inlined. This value may go negative.
40 // If there is only one call of the function, and it has internal linkage,
41 // make it almost guaranteed to be inlined.
43 if (Callee->use_size() == 1 && Callee->hasInternalLinkage())
46 // Add to the inline quality for properties that make the call valueable to
47 // inline. This includes factors that indicate that the result of inlining
48 // the function will be optimizable. Currently this just looks at arguments
49 // passed into the function.
51 for (CallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end();
53 // Each argument passed in has a cost at both the caller and the callee
54 // sides. This favors functions that take many arguments over functions
55 // that take few arguments.
58 // If this is a function being passed in, it is very likely that we will be
59 // able to turn an indirect function call into a direct function call.
63 // If a constant, global variable or alloca is passed in, inlining this
64 // function is likely to allow significant future optimization possibilities
65 // (constant propagation, scalar promotion, and scalarization), so encourage
66 // the inlining of the function.
68 else if (isa<Constant>(I) || isa<GlobalVariable>(I) || isa<AllocaInst>(I))
72 // Now that we have considered all of the factors that make the call site more
73 // likely to be inlined, look at factors that make us not want to inline it.
74 // As soon as the inline quality gets negative, bail out.
76 // Look at the size of the callee. Each basic block counts as 20 units, and
77 // each instruction counts as 10.
78 for (Function::const_iterator BB = Callee->begin(), E = Callee->end();
80 InlineCost += BB->size()*10 + 20;
82 // Don't inline into something too big, which would make it bigger. Here, we
83 // count each basic block as a single unit.
84 for (Function::const_iterator BB = Caller->begin(), E = Caller->end();