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and documentation updates soo. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@28495 91177308-0d34-0410-b5e6-96231b3b80d8
159 lines
5.2 KiB
C++
159 lines
5.2 KiB
C++
//===-- LCSSA.cpp - Convert loops into loop-closed SSA form ------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file was developed by Owen Anderson and is distributed under the
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// University of Illinois Open Source License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This pass transforms loops by placing phi nodes at the end of the loops for
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// all values that are live across the loop boundary. For example, it turns
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// the left into the right code:
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//
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// for (...) for (...)
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// if (c) if(c)
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// X1 = ... X1 = ...
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// else else
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// X2 = ... X2 = ...
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// X3 = phi(X1, X2) X3 = phi(X1, X2)
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// ... = X3 + 4 X4 = phi(X3)
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// ... = X4 + 4
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//
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// This is still valid LLVM; the extra phi nodes are purely redundant, and will
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// be trivially eliminated by InstCombine. The major benefit of this
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// transformation is that it makes many other loop optimizations, such as
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// LoopUnswitching, simpler.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Pass.h"
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#include "llvm/Function.h"
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#include "llvm/Instructions.h"
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#include "llvm/Analysis/LoopInfo.h"
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#include "llvm/Support/CFG.h"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/Transforms/Utils/BasicBlockUtils.h"
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#include <iostream>
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#include <set>
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#include <vector>
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using namespace llvm;
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namespace {
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class LCSSA : public FunctionPass {
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public:
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LoopInfo *LI; // Loop information
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// LoopProcessWorklist - List of loops we need to process.
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std::vector<Loop*> LoopProcessWorklist;
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virtual bool runOnFunction(Function &F);
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bool visitLoop(Loop *L, Value *V);
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/// This transformation requires natural loop information & requires that
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/// loop preheaders be inserted into the CFG...
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///
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequiredID(LoopSimplifyID);
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AU.addPreservedID(LoopSimplifyID);
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AU.addRequired<LoopInfo>();
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AU.addPreserved<LoopInfo>();
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}
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private:
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void addSubloopsToWorklist(Loop* L);
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std::set<Value*> loopValuesUsedOutsideLoop(Loop *L);
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};
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RegisterOpt<LCSSA> X("lcssa", "Loop-Closed SSA Form Pass");
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}
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FunctionPass *llvm::createLCSSAPass() { return new LCSSA(); }
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bool LCSSA::runOnFunction(Function &F) {
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bool changed = false;
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LI = &getAnalysis<LoopInfo>();
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for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I) {
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addSubloopsToWorklist(*I);
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LoopProcessWorklist.push_back(*I);
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}
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for (std::vector<Loop*>::iterator I = LoopProcessWorklist.begin(),
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E = LoopProcessWorklist.end(); I != E; ++I) {
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std::set<Value*> AffectedValues = loopValuesUsedOutsideLoop(*I);
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if (!AffectedValues.empty()) {
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for (std::set<Value*>::iterator VI = AffectedValues.begin(),
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VE = AffectedValues.end(); VI != VE; ++VI)
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changed |= visitLoop(*I, *VI);
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}
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}
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return changed;
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}
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bool LCSSA::visitLoop(Loop *L, Value* V) {
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// We will be doing lots of "loop contains block" queries. Loop::contains is
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// linear time, use a set to speed this up.
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std::set<BasicBlock*> LoopBlocks;
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for (Loop::block_iterator BB = L->block_begin(), E = L->block_end();
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BB != E; ++BB)
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LoopBlocks.insert(*BB);
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std::vector<BasicBlock*> exitBlocks;
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L->getExitBlocks(exitBlocks);
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for (std::vector<BasicBlock*>::iterator BBI = exitBlocks.begin(),
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BBE = exitBlocks.end(); BBI != BBE; ++BBI) {
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PHINode *phi = new PHINode(V->getType(), "lcssa");
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(*BBI)->getInstList().insert((*BBI)->front(), phi);
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for (pred_iterator PI = pred_begin(*BBI), PE = pred_end(*BBI); PI != PE;
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++PI)
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phi->addIncoming(V, *PI);
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}
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for (Value::use_iterator UI = V->use_begin(), UE = V->use_end(); UI != UE;
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++UI) {
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BasicBlock *UserBB = cast<Instruction>(*UI)->getParent();
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if (!LoopBlocks.count(UserBB))
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; // FIXME: This should update the SSA form through the rest of the graph.
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}
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return false;
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}
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void LCSSA::addSubloopsToWorklist(Loop* L) {
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for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I) {
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addSubloopsToWorklist(*I);
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LoopProcessWorklist.push_back(*I);
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}
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}
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/// loopValuesUsedOutsideLoop - Return true if there are any values defined in
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/// the loop that are used by instructions outside of it.
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std::set<Value*> LCSSA::loopValuesUsedOutsideLoop(Loop *L) {
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std::set<Value*> AffectedValues;
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// We will be doing lots of "loop contains block" queries. Loop::contains is
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// linear time, use a set to speed this up.
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std::set<BasicBlock*> LoopBlocks;
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for (Loop::block_iterator BB = L->block_begin(), E = L->block_end();
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BB != E; ++BB)
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LoopBlocks.insert(*BB);
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for (Loop::block_iterator BB = L->block_begin(), E = L->block_end();
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BB != E; ++BB) {
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for (BasicBlock::iterator I = (*BB)->begin(), E = (*BB)->end(); I != E; ++I)
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for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E;
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++UI) {
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BasicBlock *UserBB = cast<Instruction>(*UI)->getParent();
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if (!LoopBlocks.count(UserBB))
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AffectedValues.insert(I);
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}
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}
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return AffectedValues;
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} |