mirror of
https://github.com/c64scene-ar/llvm-6502.git
synced 2024-09-01 19:29:22 +00:00
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@51890 91177308-0d34-0410-b5e6-96231b3b80d8
294 lines
11 KiB
C++
294 lines
11 KiB
C++
//===-- LCSSA.cpp - Convert loops into loop-closed SSA form ---------------===//
|
|
//
|
|
// The LLVM Compiler Infrastructure
|
|
//
|
|
// This file is distributed under the University of Illinois Open Source
|
|
// License. See LICENSE.TXT for details.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
//
|
|
// This pass transforms loops by placing phi nodes at the end of the loops for
|
|
// all values that are live across the loop boundary. For example, it turns
|
|
// the left into the right code:
|
|
//
|
|
// for (...) for (...)
|
|
// if (c) if (c)
|
|
// X1 = ... X1 = ...
|
|
// else else
|
|
// X2 = ... X2 = ...
|
|
// X3 = phi(X1, X2) X3 = phi(X1, X2)
|
|
// ... = X3 + 4 X4 = phi(X3)
|
|
// ... = X4 + 4
|
|
//
|
|
// This is still valid LLVM; the extra phi nodes are purely redundant, and will
|
|
// be trivially eliminated by InstCombine. The major benefit of this
|
|
// transformation is that it makes many other loop optimizations, such as
|
|
// LoopUnswitching, simpler.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
#define DEBUG_TYPE "lcssa"
|
|
#include "llvm/Transforms/Scalar.h"
|
|
#include "llvm/Constants.h"
|
|
#include "llvm/Pass.h"
|
|
#include "llvm/Function.h"
|
|
#include "llvm/Instructions.h"
|
|
#include "llvm/ADT/SetVector.h"
|
|
#include "llvm/ADT/Statistic.h"
|
|
#include "llvm/Analysis/Dominators.h"
|
|
#include "llvm/Analysis/LoopPass.h"
|
|
#include "llvm/Analysis/ScalarEvolution.h"
|
|
#include "llvm/Support/CFG.h"
|
|
#include "llvm/Support/Compiler.h"
|
|
#include <algorithm>
|
|
#include <map>
|
|
using namespace llvm;
|
|
|
|
STATISTIC(NumLCSSA, "Number of live out of a loop variables");
|
|
|
|
namespace {
|
|
struct VISIBILITY_HIDDEN LCSSA : public LoopPass {
|
|
static char ID; // Pass identification, replacement for typeid
|
|
LCSSA() : LoopPass((intptr_t)&ID) {}
|
|
|
|
// Cached analysis information for the current function.
|
|
LoopInfo *LI;
|
|
DominatorTree *DT;
|
|
std::vector<BasicBlock*> LoopBlocks;
|
|
|
|
virtual bool runOnLoop(Loop *L, LPPassManager &LPM);
|
|
|
|
void ProcessInstruction(Instruction* Instr,
|
|
const SmallVector<BasicBlock*, 8>& exitBlocks);
|
|
|
|
/// This transformation requires natural loop information & requires that
|
|
/// loop preheaders be inserted into the CFG. It maintains both of these,
|
|
/// as well as the CFG. It also requires dominator information.
|
|
///
|
|
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
|
|
AU.setPreservesCFG();
|
|
AU.addRequiredID(LoopSimplifyID);
|
|
AU.addPreservedID(LoopSimplifyID);
|
|
AU.addRequired<LoopInfo>();
|
|
AU.addPreserved<LoopInfo>();
|
|
AU.addRequired<DominatorTree>();
|
|
AU.addPreserved<ScalarEvolution>();
|
|
AU.addPreserved<DominatorTree>();
|
|
|
|
// Request DominanceFrontier now, even though LCSSA does
|
|
// not use it. This allows Pass Manager to schedule Dominance
|
|
// Frontier early enough such that one LPPassManager can handle
|
|
// multiple loop transformation passes.
|
|
AU.addRequired<DominanceFrontier>();
|
|
AU.addPreserved<DominanceFrontier>();
|
|
}
|
|
private:
|
|
void getLoopValuesUsedOutsideLoop(Loop *L,
|
|
SetVector<Instruction*> &AffectedValues);
|
|
|
|
Value *GetValueForBlock(DomTreeNode *BB, Instruction *OrigInst,
|
|
DenseMap<DomTreeNode*, Value*> &Phis);
|
|
|
|
/// inLoop - returns true if the given block is within the current loop
|
|
bool inLoop(BasicBlock* B) {
|
|
return std::binary_search(LoopBlocks.begin(), LoopBlocks.end(), B);
|
|
}
|
|
};
|
|
}
|
|
|
|
char LCSSA::ID = 0;
|
|
static RegisterPass<LCSSA> X("lcssa", "Loop-Closed SSA Form Pass");
|
|
|
|
LoopPass *llvm::createLCSSAPass() { return new LCSSA(); }
|
|
const PassInfo *const llvm::LCSSAID = &X;
|
|
|
|
/// runOnFunction - Process all loops in the function, inner-most out.
|
|
bool LCSSA::runOnLoop(Loop *L, LPPassManager &LPM) {
|
|
|
|
LI = &LPM.getAnalysis<LoopInfo>();
|
|
DT = &getAnalysis<DominatorTree>();
|
|
|
|
// Speed up queries by creating a sorted list of blocks
|
|
LoopBlocks.clear();
|
|
LoopBlocks.insert(LoopBlocks.end(), L->block_begin(), L->block_end());
|
|
std::sort(LoopBlocks.begin(), LoopBlocks.end());
|
|
|
|
SetVector<Instruction*> AffectedValues;
|
|
getLoopValuesUsedOutsideLoop(L, AffectedValues);
|
|
|
|
// If no values are affected, we can save a lot of work, since we know that
|
|
// nothing will be changed.
|
|
if (AffectedValues.empty())
|
|
return false;
|
|
|
|
SmallVector<BasicBlock*, 8> exitBlocks;
|
|
L->getExitBlocks(exitBlocks);
|
|
|
|
// Iterate over all affected values for this loop and insert Phi nodes
|
|
// for them in the appropriate exit blocks
|
|
|
|
for (SetVector<Instruction*>::iterator I = AffectedValues.begin(),
|
|
E = AffectedValues.end(); I != E; ++I)
|
|
ProcessInstruction(*I, exitBlocks);
|
|
|
|
assert(L->isLCSSAForm());
|
|
|
|
return true;
|
|
}
|
|
|
|
/// processInstruction - Given a live-out instruction, insert LCSSA Phi nodes,
|
|
/// eliminate all out-of-loop uses.
|
|
void LCSSA::ProcessInstruction(Instruction *Instr,
|
|
const SmallVector<BasicBlock*, 8>& exitBlocks) {
|
|
++NumLCSSA; // We are applying the transformation
|
|
|
|
// Keep track of the blocks that have the value available already.
|
|
DenseMap<DomTreeNode*, Value*> Phis;
|
|
|
|
DomTreeNode *InstrNode = DT->getNode(Instr->getParent());
|
|
|
|
// Insert the LCSSA phi's into the exit blocks (dominated by the value), and
|
|
// add them to the Phi's map.
|
|
for (SmallVector<BasicBlock*, 8>::const_iterator BBI = exitBlocks.begin(),
|
|
BBE = exitBlocks.end(); BBI != BBE; ++BBI) {
|
|
BasicBlock *BB = *BBI;
|
|
DomTreeNode *ExitBBNode = DT->getNode(BB);
|
|
Value *&Phi = Phis[ExitBBNode];
|
|
if (!Phi && DT->dominates(InstrNode, ExitBBNode)) {
|
|
PHINode *PN = PHINode::Create(Instr->getType(), Instr->getName()+".lcssa",
|
|
BB->begin());
|
|
PN->reserveOperandSpace(std::distance(pred_begin(BB), pred_end(BB)));
|
|
|
|
// Remember that this phi makes the value alive in this block.
|
|
Phi = PN;
|
|
|
|
// Add inputs from inside the loop for this PHI.
|
|
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
|
|
PN->addIncoming(Instr, *PI);
|
|
}
|
|
}
|
|
|
|
|
|
// Record all uses of Instr outside the loop. We need to rewrite these. The
|
|
// LCSSA phis won't be included because they use the value in the loop.
|
|
for (Value::use_iterator UI = Instr->use_begin(), E = Instr->use_end();
|
|
UI != E;) {
|
|
BasicBlock *UserBB = cast<Instruction>(*UI)->getParent();
|
|
if (PHINode *P = dyn_cast<PHINode>(*UI)) {
|
|
unsigned OperandNo = UI.getOperandNo();
|
|
UserBB = P->getIncomingBlock(OperandNo/2);
|
|
}
|
|
|
|
// If the user is in the loop, don't rewrite it!
|
|
if (UserBB == Instr->getParent() || inLoop(UserBB)) {
|
|
++UI;
|
|
continue;
|
|
}
|
|
|
|
// Otherwise, patch up uses of the value with the appropriate LCSSA Phi,
|
|
// inserting PHI nodes into join points where needed.
|
|
Value *Val = GetValueForBlock(DT->getNode(UserBB), Instr, Phis);
|
|
|
|
// Preincrement the iterator to avoid invalidating it when we change the
|
|
// value.
|
|
Use &U = UI.getUse();
|
|
++UI;
|
|
U.set(Val);
|
|
}
|
|
}
|
|
|
|
/// getLoopValuesUsedOutsideLoop - Return any values defined in the loop that
|
|
/// are used by instructions outside of it.
|
|
void LCSSA::getLoopValuesUsedOutsideLoop(Loop *L,
|
|
SetVector<Instruction*> &AffectedValues) {
|
|
// FIXME: For large loops, we may be able to avoid a lot of use-scanning
|
|
// by using dominance information. In particular, if a block does not
|
|
// dominate any of the loop exits, then none of the values defined in the
|
|
// block could be used outside the loop.
|
|
for (Loop::block_iterator BB = L->block_begin(), E = L->block_end();
|
|
BB != E; ++BB) {
|
|
for (BasicBlock::iterator I = (*BB)->begin(), E = (*BB)->end(); I != E; ++I)
|
|
for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E;
|
|
++UI) {
|
|
BasicBlock *UserBB = cast<Instruction>(*UI)->getParent();
|
|
if (PHINode* p = dyn_cast<PHINode>(*UI)) {
|
|
unsigned OperandNo = UI.getOperandNo();
|
|
UserBB = p->getIncomingBlock(OperandNo/2);
|
|
}
|
|
|
|
if (*BB != UserBB && !inLoop(UserBB)) {
|
|
const StructType *STy = dyn_cast<StructType>(I->getType());
|
|
if (STy) {
|
|
// I is a call or an invoke that returns multiple values.
|
|
// These values are accessible through getresult only.
|
|
// If the getresult value is not in the BB then move it
|
|
// immediately here. It will be processed in next iteration.
|
|
BasicBlock::iterator InsertPoint;
|
|
if (InvokeInst *II = dyn_cast<InvokeInst>(I)) {
|
|
InsertPoint = II->getNormalDest()->getFirstNonPHI();
|
|
} else {
|
|
InsertPoint = I;
|
|
InsertPoint++;
|
|
}
|
|
for (Value::use_iterator TmpI = I->use_begin(),
|
|
TmpE = I->use_end(); TmpI != TmpE; ++TmpI) {
|
|
GetResultInst *GR = cast<GetResultInst>(TmpI);
|
|
if (GR->getParent() != *BB)
|
|
GR->moveBefore(InsertPoint);
|
|
}
|
|
} else
|
|
AffectedValues.insert(I);
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
/// GetValueForBlock - Get the value to use within the specified basic block.
|
|
/// available values are in Phis.
|
|
Value *LCSSA::GetValueForBlock(DomTreeNode *BB, Instruction *OrigInst,
|
|
DenseMap<DomTreeNode*, Value*> &Phis) {
|
|
// If there is no dominator info for this BB, it is unreachable.
|
|
if (BB == 0)
|
|
return UndefValue::get(OrigInst->getType());
|
|
|
|
// If we have already computed this value, return the previously computed val.
|
|
if (Phis.count(BB)) return Phis[BB];
|
|
|
|
DomTreeNode *IDom = BB->getIDom();
|
|
|
|
// Otherwise, there are two cases: we either have to insert a PHI node or we
|
|
// don't. We need to insert a PHI node if this block is not dominated by one
|
|
// of the exit nodes from the loop (the loop could have multiple exits, and
|
|
// though the value defined *inside* the loop dominated all its uses, each
|
|
// exit by itself may not dominate all the uses).
|
|
//
|
|
// The simplest way to check for this condition is by checking to see if the
|
|
// idom is in the loop. If so, we *know* that none of the exit blocks
|
|
// dominate this block. Note that we *know* that the block defining the
|
|
// original instruction is in the idom chain, because if it weren't, then the
|
|
// original value didn't dominate this use.
|
|
if (!inLoop(IDom->getBlock())) {
|
|
// Idom is not in the loop, we must still be "below" the exit block and must
|
|
// be fully dominated by the value live in the idom.
|
|
Value* val = GetValueForBlock(IDom, OrigInst, Phis);
|
|
Phis.insert(std::make_pair(BB, val));
|
|
return val;
|
|
}
|
|
|
|
BasicBlock *BBN = BB->getBlock();
|
|
|
|
// Otherwise, the idom is the loop, so we need to insert a PHI node. Do so
|
|
// now, then get values to fill in the incoming values for the PHI.
|
|
PHINode *PN = PHINode::Create(OrigInst->getType(),
|
|
OrigInst->getName() + ".lcssa", BBN->begin());
|
|
PN->reserveOperandSpace(std::distance(pred_begin(BBN), pred_end(BBN)));
|
|
Phis.insert(std::make_pair(BB, PN));
|
|
|
|
// Fill in the incoming values for the block.
|
|
for (pred_iterator PI = pred_begin(BBN), E = pred_end(BBN); PI != E; ++PI)
|
|
PN->addIncoming(GetValueForBlock(DT->getNode(*PI), OrigInst, Phis), *PI);
|
|
return PN;
|
|
}
|
|
|