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//===- InlineSimple.cpp - Code to perform simple function inlining --------===//
//
// This file implements bottom-up inlining of functions into callees.
//
//===----------------------------------------------------------------------===//
#include "Inliner.h"
#include "llvm/Function.h"
#include "llvm/iMemory.h"
#include "llvm/Support/CallSite.h"
#include "llvm/Transforms/IPO.h"
namespace {
struct SimpleInliner : public Inliner {
int getInlineCost(CallSite CS);
};
RegisterOpt<SimpleInliner> X("inline", "Function Integration/Inlining");
}
Pass *createFunctionInliningPass() { return new SimpleInliner(); }
// getInlineCost - The heuristic used to determine if we should inline the
// function call or not.
//
int SimpleInliner::getInlineCost(CallSite CS) {
Instruction *TheCall = CS.getInstruction();
const Function *Callee = CS.getCalledFunction();
const Function *Caller = TheCall->getParent()->getParent();
// Don't inline a directly recursive call.
if (Caller == Callee) return 2000000000;
// InlineCost - This value measures how good of an inline candidate this call
// site is to inline. A lower inline cost make is more likely for the call to
// be inlined. This value may go negative.
//
int InlineCost = 0;
// If there is only one call of the function, and it has internal linkage,
// make it almost guaranteed to be inlined.
//
if (Callee->use_size() == 1 && Callee->hasInternalLinkage())
InlineCost -= 30000;
// Add to the inline quality for properties that make the call valueable to
// inline. This includes factors that indicate that the result of inlining
// the function will be optimizable. Currently this just looks at arguments
// passed into the function.
//
for (CallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end();
I != E; ++I) {
// Each argument passed in has a cost at both the caller and the callee
// sides. This favors functions that take many arguments over functions
// that take few arguments.
InlineCost -= 20;
// If this is a function being passed in, it is very likely that we will be
// able to turn an indirect function call into a direct function call.
if (isa<Function>(I))
InlineCost -= 100;
// If a constant, global variable or alloca is passed in, inlining this
// function is likely to allow significant future optimization possibilities
// (constant propagation, scalar promotion, and scalarization), so encourage
// the inlining of the function.
//
else if (isa<Constant>(I) || isa<GlobalVariable>(I) || isa<AllocaInst>(I))
InlineCost -= 60;
}
// Now that we have considered all of the factors that make the call site more
// likely to be inlined, look at factors that make us not want to inline it.
// As soon as the inline quality gets negative, bail out.
// Look at the size of the callee. Each basic block counts as 20 units, and
// each instruction counts as 10.
for (Function::const_iterator BB = Callee->begin(), E = Callee->end();
BB != E; ++BB)
InlineCost += BB->size()*10 + 20;
// Don't inline into something too big, which would make it bigger. Here, we
// count each basic block as a single unit.
for (Function::const_iterator BB = Caller->begin(), E = Caller->end();
BB != E; ++BB)
InlineCost++;
return InlineCost;
}
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