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https://github.com/c64scene-ar/llvm-6502.git
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@7492 91177308-0d34-0410-b5e6-96231b3b80d8
174 lines
6.3 KiB
C++
174 lines
6.3 KiB
C++
//===- FunctionInlining.cpp - Code to perform 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 "llvm/Transforms/IPO.h"
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#include "llvm/Transforms/Utils/Cloning.h"
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#include "llvm/Module.h"
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#include "llvm/Pass.h"
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#include "llvm/iOther.h"
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#include "llvm/iMemory.h"
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#include "Support/CommandLine.h"
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#include "Support/Debug.h"
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#include "Support/Statistic.h"
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#include <set>
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namespace {
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Statistic<> NumInlined("inline", "Number of functions inlined");
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cl::opt<unsigned> // FIXME: 200 is VERY conservative
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InlineLimit("inline-threshold", cl::Hidden, cl::init(200),
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cl::desc("Control the amount of inlining to perform (default = 200)"));
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struct FunctionInlining : public Pass {
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virtual bool run(Module &M) {
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bool Changed = false;
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for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
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Changed |= doInlining(I);
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ProcessedFunctions.clear();
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return Changed;
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}
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private:
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std::set<Function*> ProcessedFunctions; // Prevent infinite recursion
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bool doInlining(Function *F);
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};
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RegisterOpt<FunctionInlining> X("inline", "Function Integration/Inlining");
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}
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Pass *createFunctionInliningPass() { return new FunctionInlining(); }
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// ShouldInlineFunction - The heuristic used to determine if we should inline
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// the function call or not.
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//
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static inline bool ShouldInlineFunction(const CallInst *CI) {
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assert(CI->getParent() && CI->getParent()->getParent() &&
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"Call not embedded into a function!");
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const Function *Callee = CI->getCalledFunction();
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if (Callee == 0 || Callee->isExternal())
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return false; // Cannot inline an indirect call... or external function.
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// Don't inline a recursive call.
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const Function *Caller = CI->getParent()->getParent();
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if (Caller == Callee) return false;
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// InlineQuality - This value measures how good of an inline candidate this
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// call site is to inline. The initial value determines how aggressive the
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// inliner is. If this value is negative after the final computation,
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// inlining is not performed.
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//
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int InlineQuality = InlineLimit;
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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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InlineQuality += 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 (User::const_op_iterator I = CI->op_begin()+1, E = CI->op_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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InlineQuality += 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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InlineQuality += 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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InlineQuality += 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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InlineQuality -= BB->size()*10 + 20;
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if (InlineQuality < 0) return false;
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}
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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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--InlineQuality;
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if (InlineQuality < 0) return false;
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}
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// If we get here, this call site is high enough "quality" to inline.
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DEBUG(std::cerr << "Inlining in '" << Caller->getName()
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<< "', quality = " << InlineQuality << ": " << *CI);
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return true;
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}
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// doInlining - Use a heuristic based approach to inline functions that seem to
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// look good.
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//
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bool FunctionInlining::doInlining(Function *F) {
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// If we have already processed this function (ie, it is recursive) don't
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// revisit.
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std::set<Function*>::iterator PFI = ProcessedFunctions.lower_bound(F);
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if (PFI != ProcessedFunctions.end() && *PFI == F) return false;
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// Insert the function in the set so it doesn't get revisited.
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ProcessedFunctions.insert(PFI, F);
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bool Changed = false;
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for (Function::iterator BB = F->begin(); BB != F->end(); ++BB)
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for (BasicBlock::iterator I = BB->begin(); I != BB->end(); ) {
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bool ShouldInc = true;
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// Found a call instruction? FIXME: This should also handle INVOKEs
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if (CallInst *CI = dyn_cast<CallInst>(I)) {
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if (Function *Callee = CI->getCalledFunction())
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doInlining(Callee); // Inline in callees before callers!
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// Decide whether we should inline this function...
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if (ShouldInlineFunction(CI)) {
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// Save an iterator to the instruction before the call if it exists,
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// otherwise get an iterator at the end of the block... because the
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// call will be destroyed.
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//
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BasicBlock::iterator SI;
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if (I != BB->begin()) {
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SI = I; --SI; // Instruction before the call...
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} else {
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SI = BB->end();
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}
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// Attempt to inline the function...
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if (InlineFunction(CI)) {
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++NumInlined;
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Changed = true;
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// Move to instruction before the call...
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I = (SI == BB->end()) ? BB->begin() : SI;
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ShouldInc = false; // Don't increment iterator until next time
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}
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}
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}
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if (ShouldInc) ++I;
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}
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return Changed;
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}
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