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237ef567f6
* Separate the policy decisions into a derived class [InlineSimple]
* Move the inlining mechanics into a base class [Inliner]
* Change the inliner to be an SCCPass, making it more structured and
eventually pipelinable with other SCC passes
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@8257 91177308-0d34-0410-b5e6-96231b3b80d8
90 lines
3.3 KiB
C++
90 lines
3.3 KiB
C++
//===- InlineSimple.cpp - Code to perform simple function inlining --------===//
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//
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// This file implements bottom-up inlining of functions into callees.
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//
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//===----------------------------------------------------------------------===//
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#include "Inliner.h"
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#include "llvm/Function.h"
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#include "llvm/iMemory.h"
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#include "llvm/Support/CallSite.h"
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#include "llvm/Transforms/IPO.h"
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namespace {
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struct SimpleInliner : public Inliner {
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int getInlineCost(CallSite CS);
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};
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RegisterOpt<SimpleInliner> X("inline", "Function Integration/Inlining");
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}
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Pass *createFunctionInliningPass() { return new SimpleInliner(); }
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// getInlineCost - The heuristic used to determine if we should inline the
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// function call or not.
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//
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int SimpleInliner::getInlineCost(CallSite CS) {
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Instruction *TheCall = CS.getInstruction();
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const Function *Callee = CS.getCalledFunction();
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const Function *Caller = TheCall->getParent()->getParent();
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// Don't inline a directly recursive call.
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if (Caller == Callee) return 2000000000;
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// InlineCost - This value measures how good of an inline candidate this call
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// site is to inline. A lower inline cost make is more likely for the call to
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// be inlined. This value may go negative.
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//
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int InlineCost = 0;
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// If there is only one call of the function, and it has internal linkage,
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// make it almost guaranteed to be inlined.
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//
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if (Callee->use_size() == 1 && Callee->hasInternalLinkage())
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InlineCost -= 30000;
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// Add to the inline quality for properties that make the call valueable to
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// inline. This includes factors that indicate that the result of inlining
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// the function will be optimizable. Currently this just looks at arguments
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// passed into the function.
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//
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for (CallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end();
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I != E; ++I) {
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// Each argument passed in has a cost at both the caller and the callee
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// sides. This favors functions that take many arguments over functions
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// that take few arguments.
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InlineCost -= 20;
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// If this is a function being passed in, it is very likely that we will be
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// able to turn an indirect function call into a direct function call.
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if (isa<Function>(I))
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InlineCost -= 100;
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// If a constant, global variable or alloca is passed in, inlining this
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// function is likely to allow significant future optimization possibilities
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// (constant propagation, scalar promotion, and scalarization), so encourage
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// the inlining of the function.
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//
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else if (isa<Constant>(I) || isa<GlobalVariable>(I) || isa<AllocaInst>(I))
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InlineCost -= 60;
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}
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// Now that we have considered all of the factors that make the call site more
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// likely to be inlined, look at factors that make us not want to inline it.
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// As soon as the inline quality gets negative, bail out.
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// Look at the size of the callee. Each basic block counts as 20 units, and
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// each instruction counts as 10.
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for (Function::const_iterator BB = Callee->begin(), E = Callee->end();
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BB != E; ++BB)
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InlineCost += BB->size()*10 + 20;
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// Don't inline into something too big, which would make it bigger. Here, we
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// count each basic block as a single unit.
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for (Function::const_iterator BB = Caller->begin(), E = Caller->end();
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BB != E; ++BB)
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InlineCost++;
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return InlineCost;
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}
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