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Lots of changes based on review and new functionality:
* Use a git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@21546 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Reid Spencer
parent
8b9f9b3d60
commit
6cc0311c6d
@ -19,9 +19,12 @@
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#include "llvm/Transforms/IPO.h"
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#include "llvm/Module.h"
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#include "llvm/Pass.h"
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#include "llvm/DerivedTypes.h"
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#include "llvm/Constants.h"
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#include "llvm/Instructions.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/ADT/hash_map"
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#include <iostream>
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using namespace llvm;
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namespace {
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@ -58,6 +61,19 @@ namespace {
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virtual ~CallOptimizer();
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/// The implementation of this function in subclasses should determine if
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/// \p F is suitable for the optimization. This method is called by
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/// runOnModule to short circuit visiting all the call sites of such a
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/// function if that function is not suitable in the first place.
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/// If the called function is suitabe, this method should return true;
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/// false, otherwise. This function should also perform any lazy
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/// initialization that the CallOptimizer needs to do, if its to return
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/// true. This avoids doing initialization until the optimizer is actually
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/// going to be called upon to do some optimization.
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virtual bool ValidateCalledFunction(
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const Function* F ///< The function that is the target of call sites
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) const = 0;
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/// The implementations of this function in subclasses is the heart of the
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/// SimplifyLibCalls algorithm. Sublcasses of this class implement
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/// OptimizeCall to determine if (a) the conditions are right for optimizing
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@ -67,14 +83,17 @@ namespace {
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/// @param ci the call instruction under consideration
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/// @param f the function that ci calls.
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/// @brief Optimize a call, if possible.
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virtual bool OptimizeCall(CallInst* ci) const = 0;
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virtual bool OptimizeCall(
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CallInst* ci ///< The call instruction that should be optimized.
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) const = 0;
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const std::string& getFunctionName() const { return func_name; }
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const char * getFunctionName() const { return func_name; }
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private:
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std::string func_name;
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const char* func_name;
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};
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/// @brief The list of optimizations deriving from CallOptimizer
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hash_map<std::string,CallOptimizer*> optlist;
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CallOptimizer::CallOptimizer(const char* fname)
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@ -85,7 +104,10 @@ namespace {
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}
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/// Make sure we get our virtual table in this file.
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CallOptimizer::~CallOptimizer() {}
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CallOptimizer::~CallOptimizer()
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{
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optlist.clear();
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}
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}
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ModulePass *llvm::createSimplifyLibCallsPass()
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@ -95,35 +117,52 @@ ModulePass *llvm::createSimplifyLibCallsPass()
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bool SimplifyLibCalls::runOnModule(Module &M)
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{
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for (Module::iterator FI = M.begin(), FE = M.end(); FI != FE; ++FI)
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bool result = false;
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// The call optimizations can be recursive. That is, the optimization might
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// generate a call to another function which can also be optimized. This way
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// we make the CallOptimizer instances very specific to the case they handle.
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// It also means we need to keep running over the function calls in the module
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// until we don't get any more optimizations possible.
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bool found_optimization = false;
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do
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{
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// All the "well-known" functions are external because they live in a
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// runtime library somewhere and were (probably) not compiled by LLVM.
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// So, we only act on external functions that have non-empty uses.
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if (FI->isExternal() && !FI->use_empty())
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found_optimization = false;
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for (Module::iterator FI = M.begin(), FE = M.end(); FI != FE; ++FI)
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{
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// Get the optimization class that pertains to this function
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if (CallOptimizer* CO = optlist[FI->getName()] )
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// All the "well-known" functions are external and have external linkage
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// because they live in a runtime library somewhere and were (probably)
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// not compiled by LLVM. So, we only act on external functions that have
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// external linkage and non-empty uses.
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if (FI->isExternal() && FI->hasExternalLinkage() && !FI->use_empty())
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{
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// Loop over each of the uses of the function
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for (Value::use_iterator UI = FI->use_begin(), UE = FI->use_end();
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UI != UE ; )
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// Get the optimization class that pertains to this function
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if (CallOptimizer* CO = optlist[FI->getName().c_str()] )
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{
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// If the use of the function is a call instruction
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if (CallInst* CI = dyn_cast<CallInst>(*UI++))
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// Make sure the called function is suitable for the optimization
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if (CO->ValidateCalledFunction(FI))
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{
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// Do the optimization on the CallOptimizer we found earlier.
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if (CO->OptimizeCall(CI))
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// Loop over each of the uses of the function
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for (Value::use_iterator UI = FI->use_begin(), UE = FI->use_end();
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UI != UE ; )
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{
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++SimplifiedLibCalls;
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break;
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// If the use of the function is a call instruction
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if (CallInst* CI = dyn_cast<CallInst>(*UI++))
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{
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// Do the optimization on the CallOptimizer.
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if (CO->OptimizeCall(CI))
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{
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++SimplifiedLibCalls;
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found_optimization = result = true;
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}
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}
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}
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}
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}
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}
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}
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}
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return true;
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} while (found_optimization);
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return result;
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}
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namespace {
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@ -138,47 +177,226 @@ struct ExitInMainOptimization : public CallOptimizer
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{
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ExitInMainOptimization() : CallOptimizer("exit") {}
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virtual ~ExitInMainOptimization() {}
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// Make sure the called function looks like exit (int argument, int return
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// type, external linkage, not varargs).
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virtual bool ValidateCalledFunction(const Function* f) const
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{
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if (f->getReturnType()->getTypeID() == Type::VoidTyID && !f->isVarArg())
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if (f->arg_size() == 1)
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if (f->arg_begin()->getType()->isInteger())
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return true;
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return false;
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}
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virtual bool OptimizeCall(CallInst* ci) const
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{
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// If the call isn't coming from main or main doesn't have external linkage
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// or the return type of main is not the same as the type of the exit(3)
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// argument then we don't act
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if (const Function* f = ci->getParent()->getParent())
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if (!(f->hasExternalLinkage() &&
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(f->getReturnType() == ci->getOperand(1)->getType()) &&
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(f->getName() == "main")))
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return false;
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// To be careful, we check that the call to exit is coming from "main", that
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// main has external linkage, and the return type of main and the argument
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// to exit have the same type.
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Function *from = ci->getParent()->getParent();
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if (from->hasExternalLinkage())
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if (from->getReturnType() == ci->getOperand(1)->getType())
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if (from->getName() == "main")
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{
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// Okay, time to actually do the optimization. First, get the basic
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// block of the call instruction
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BasicBlock* bb = ci->getParent();
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// Okay, time to replace it. Get the basic block of the call instruction
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BasicBlock* bb = ci->getParent();
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// Create a return instruction that we'll replace the call with.
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// Note that the argument of the return is the argument of the call
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// instruction.
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ReturnInst* ri = new ReturnInst(ci->getOperand(1), ci);
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// Create a return instruction that we'll replace the call with. Note that
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// the argument of the return is the argument of the call instruction.
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ReturnInst* ri = new ReturnInst(ci->getOperand(1), ci);
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// Split the block at the call instruction which places it in a new
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// basic block.
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bb->splitBasicBlock(BasicBlock::iterator(ci));
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// Erase everything from the call instruction to the end of the block. There
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// really shouldn't be anything other than the call instruction, but just in
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// case there is we delete it all because its now dead.
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bb->getInstList().erase(ci, bb->end());
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// The block split caused a branch instruction to be inserted into
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// the end of the original block, right after the return instruction
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// that we put there. That's not a valid block, so delete the branch
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// instruction.
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bb->back().eraseFromParent();
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return true;
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// Now we can finally get rid of the call instruction which now lives
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// in the new basic block.
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ci->eraseFromParent();
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// Optimization succeeded, return true.
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return true;
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}
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// We didn't pass the criteria for this optimization so return false
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return false;
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}
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} ExitInMainOptimizer;
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/// This CallOptimizer will find instances of a call to "exit" that occurs
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/// within the "main" function and change it to a simple "ret" instruction with
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/// the same value as passed to the exit function. It assumes that the
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/// instructions after the call to exit(3) can be deleted since they are
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/// unreachable anyway.
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/// @brief Replace calls to exit in main with a simple return
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/// This CallOptimizer will simplify a call to the strcat library function. The
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/// simplification is possible only if the string being concatenated is a
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/// constant array or a constant expression that results in a constant array. In
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/// this case, if the array is small, we can generate a series of inline store
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/// instructions to effect the concatenation without calling strcat.
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/// @brief Simplify the strcat library function.
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struct StrCatOptimization : public CallOptimizer
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{
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StrCatOptimization() : CallOptimizer("strcat") {}
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virtual ~StrCatOptimization() {}
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/// @brief Make sure that the "strcat" function has the right prototype
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virtual bool ValidateCalledFunction(const Function* f) const
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{
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if (f->getReturnType() == PointerType::get(Type::SByteTy))
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if (f->arg_size() == 2)
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{
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Function::const_arg_iterator AI = f->arg_begin();
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if (AI++->getType() == PointerType::get(Type::SByteTy))
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if (AI->getType() == PointerType::get(Type::SByteTy))
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return true;
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}
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return false;
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}
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/// Perform the optimization if the length of the string concatenated
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/// is reasonably short and it is a constant array.
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virtual bool OptimizeCall(CallInst* ci) const
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{
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// If the thing being appended is not a GEP instruction
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GetElementPtrInst* GEP = dyn_cast<GetElementPtrInst>(ci->getOperand(2));
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if (!GEP)
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return false;
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// Double check that we're dealing with a pointer to sbyte here
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if (GEP->getType() != PointerType::get(Type::SByteTy))
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return false;
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// We can only optimize if the appended string is a constant
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Constant* C = dyn_cast<Constant>(GEP->getPointerOperand());
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if (!C)
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return false;
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// Check the various kinds of constants that are applicable
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GlobalVariable* GV = dyn_cast<GlobalVariable>(C);
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if (!GV)
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return false;
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// Only GVars that have initializers will do
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if (GV->hasInitializer())
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{
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Constant* INTLZR = GV->getInitializer();
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// And only if that initializer is ConstantArray
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if (ConstantArray* A = dyn_cast<ConstantArray>(INTLZR))
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{
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assert(A->isString() && "This ought to be a string");
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// Get the value of the string and determine its length. If the length
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// is zero, we can just substitute the destination pointer for the
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// call.
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std::string str = A->getAsString().c_str();
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if (str.length() == 0)
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{
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ci->replaceAllUsesWith(ci->getOperand(1));
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ci->eraseFromParent();
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return true;
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}
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// Otherwise, lets just turn this into a memcpy call which will be
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// optimized out on the next pass.
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else
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{
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// Extract some information
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Module* M = ci->getParent()->getParent()->getParent();
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// We need to find the end of the string of the first operand to the
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// strcat call instruction. That's where the memory is to be moved
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// to. So, generate code that does that
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std::vector<const Type*> args;
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args.push_back(PointerType::get(Type::SByteTy));
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FunctionType* strlen_type =
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FunctionType::get(Type::IntTy, args, false);
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Function* strlen = M->getOrInsertFunction("strlen",strlen_type);
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CallInst* strlen_inst =
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new CallInst(strlen,ci->getOperand(1),"",ci);
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// Now that we have the string length, we must add it to the pointer
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// to get the memcpy destination.
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std::vector<Value*> idx;
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idx.push_back(strlen_inst);
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GetElementPtrInst* gep =
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new GetElementPtrInst(ci->getOperand(1),idx,"",ci);
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// Generate the memcpy call
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args.clear();
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args.push_back(PointerType::get(Type::SByteTy));
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args.push_back(PointerType::get(Type::SByteTy));
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args.push_back(Type::IntTy);
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FunctionType* memcpy_type = FunctionType::get(
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PointerType::get(Type::SByteTy), args, false);
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Function* memcpy = M->getOrInsertFunction("memcpy",memcpy_type);
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std::vector<Value*> vals;
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vals.push_back(gep);
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vals.push_back(ci->getOperand(2));
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vals.push_back(ConstantSInt::get(Type::IntTy,str.length()+1));
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CallInst* memcpy_inst = new CallInst(memcpy, vals, "", ci);
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// Finally, cast the result of the memcpy to the correct type which is
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// the result of the strcat.
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CastInst* cast_inst =
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new CastInst(memcpy_inst, PointerType::get(Type::SByteTy),
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ci->getName(),ci);
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// And perform the stubstitution for the strcat call.
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ci->replaceAllUsesWith(cast_inst);
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ci->eraseFromParent();
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return true;
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}
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}
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else if (ConstantAggregateZero* CAZ =
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dyn_cast<ConstantAggregateZero>(INTLZR))
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{
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// We know this is the zero length string case so we can just avoid
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// the strcat altogether.
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ci->replaceAllUsesWith(ci->getOperand(1));
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ci->eraseFromParent();
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return true;
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}
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else if (ConstantExpr* E = dyn_cast<ConstantExpr>(INTLZR))
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{
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return false;
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}
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}
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// We didn't pass the criteria for this optimization so return false.
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return false;
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}
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} StrCatOptimizer;
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/// This CallOptimizer will simplify a call to the memcpy library function by
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/// expanding it out to a small set of stores if the copy source is a constant
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/// array.
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/// @brief Simplify the memcpy library function.
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struct MemCpyOptimization : public CallOptimizer
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{
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MemCpyOptimization() : CallOptimizer("memcpy") {}
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virtual ~MemCpyOptimization() {}
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/// @brief Make sure that the "memcpy" function has the right prototype
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virtual bool ValidateCalledFunction(const Function* f) const
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{
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if (f->getReturnType() == PointerType::get(Type::SByteTy))
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if (f->arg_size() == 2)
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{
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Function::const_arg_iterator AI = f->arg_begin();
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if (AI++->getType() == PointerType::get(Type::SByteTy))
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if (AI->getType() == PointerType::get(Type::SByteTy))
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return true;
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}
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return false;
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}
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/// Perform the optimization if the length of the string concatenated
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/// is reasonably short and it is a constant array.
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virtual bool OptimizeCall(CallInst* ci) const
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{
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// We didn't pass the criteria for this optimization so return false.
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return false;
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}
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} MemCpyOptimizer;
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}
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