mirror of
https://github.com/c64scene-ar/llvm-6502.git
synced 2024-09-02 11:30:10 +00:00
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@115996 91177308-0d34-0410-b5e6-96231b3b80d8
267 lines
9.1 KiB
C++
267 lines
9.1 KiB
C++
//===-- Sink.cpp - Code Sinking -------------------------------------------===//
|
|
//
|
|
// The LLVM Compiler Infrastructure
|
|
//
|
|
// This file is distributed under the University of Illinois Open Source
|
|
// License. See LICENSE.TXT for details.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
//
|
|
// This pass moves instructions into successor blocks, when possible, so that
|
|
// they aren't executed on paths where their results aren't needed.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
#define DEBUG_TYPE "sink"
|
|
#include "llvm/Transforms/Scalar.h"
|
|
#include "llvm/IntrinsicInst.h"
|
|
#include "llvm/Analysis/Dominators.h"
|
|
#include "llvm/Analysis/LoopInfo.h"
|
|
#include "llvm/Analysis/AliasAnalysis.h"
|
|
#include "llvm/Assembly/Writer.h"
|
|
#include "llvm/ADT/Statistic.h"
|
|
#include "llvm/Support/CFG.h"
|
|
#include "llvm/Support/Debug.h"
|
|
#include "llvm/Support/raw_ostream.h"
|
|
using namespace llvm;
|
|
|
|
STATISTIC(NumSunk, "Number of instructions sunk");
|
|
|
|
namespace {
|
|
class Sinking : public FunctionPass {
|
|
DominatorTree *DT;
|
|
LoopInfo *LI;
|
|
AliasAnalysis *AA;
|
|
|
|
public:
|
|
static char ID; // Pass identification
|
|
Sinking() : FunctionPass(ID) {}
|
|
|
|
virtual bool runOnFunction(Function &F);
|
|
|
|
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
|
|
AU.setPreservesCFG();
|
|
FunctionPass::getAnalysisUsage(AU);
|
|
AU.addRequired<AliasAnalysis>();
|
|
AU.addRequired<DominatorTree>();
|
|
AU.addRequired<LoopInfo>();
|
|
AU.addPreserved<DominatorTree>();
|
|
AU.addPreserved<LoopInfo>();
|
|
}
|
|
private:
|
|
bool ProcessBlock(BasicBlock &BB);
|
|
bool SinkInstruction(Instruction *I, SmallPtrSet<Instruction *, 8> &Stores);
|
|
bool AllUsesDominatedByBlock(Instruction *Inst, BasicBlock *BB) const;
|
|
};
|
|
} // end anonymous namespace
|
|
|
|
char Sinking::ID = 0;
|
|
INITIALIZE_PASS(Sinking, "sink", "Code sinking", false, false)
|
|
|
|
FunctionPass *llvm::createSinkingPass() { return new Sinking(); }
|
|
|
|
/// AllUsesDominatedByBlock - Return true if all uses of the specified value
|
|
/// occur in blocks dominated by the specified block.
|
|
bool Sinking::AllUsesDominatedByBlock(Instruction *Inst,
|
|
BasicBlock *BB) const {
|
|
// Ignoring debug uses is necessary so debug info doesn't affect the code.
|
|
// This may leave a referencing dbg_value in the original block, before
|
|
// the definition of the vreg. Dwarf generator handles this although the
|
|
// user might not get the right info at runtime.
|
|
for (Value::use_iterator I = Inst->use_begin(),
|
|
E = Inst->use_end(); I != E; ++I) {
|
|
// Determine the block of the use.
|
|
Instruction *UseInst = cast<Instruction>(*I);
|
|
BasicBlock *UseBlock = UseInst->getParent();
|
|
if (PHINode *PN = dyn_cast<PHINode>(UseInst)) {
|
|
// PHI nodes use the operand in the predecessor block, not the block with
|
|
// the PHI.
|
|
unsigned Num = PHINode::getIncomingValueNumForOperand(I.getOperandNo());
|
|
UseBlock = PN->getIncomingBlock(Num);
|
|
}
|
|
// Check that it dominates.
|
|
if (!DT->dominates(BB, UseBlock))
|
|
return false;
|
|
}
|
|
return true;
|
|
}
|
|
|
|
bool Sinking::runOnFunction(Function &F) {
|
|
DT = &getAnalysis<DominatorTree>();
|
|
LI = &getAnalysis<LoopInfo>();
|
|
AA = &getAnalysis<AliasAnalysis>();
|
|
|
|
bool EverMadeChange = false;
|
|
|
|
while (1) {
|
|
bool MadeChange = false;
|
|
|
|
// Process all basic blocks.
|
|
for (Function::iterator I = F.begin(), E = F.end();
|
|
I != E; ++I)
|
|
MadeChange |= ProcessBlock(*I);
|
|
|
|
// If this iteration over the code changed anything, keep iterating.
|
|
if (!MadeChange) break;
|
|
EverMadeChange = true;
|
|
}
|
|
return EverMadeChange;
|
|
}
|
|
|
|
bool Sinking::ProcessBlock(BasicBlock &BB) {
|
|
// Can't sink anything out of a block that has less than two successors.
|
|
if (BB.getTerminator()->getNumSuccessors() <= 1 || BB.empty()) return false;
|
|
|
|
// Don't bother sinking code out of unreachable blocks. In addition to being
|
|
// unprofitable, it can also lead to infinite looping, because in an unreachable
|
|
// loop there may be nowhere to stop.
|
|
if (!DT->isReachableFromEntry(&BB)) return false;
|
|
|
|
bool MadeChange = false;
|
|
|
|
// Walk the basic block bottom-up. Remember if we saw a store.
|
|
BasicBlock::iterator I = BB.end();
|
|
--I;
|
|
bool ProcessedBegin = false;
|
|
SmallPtrSet<Instruction *, 8> Stores;
|
|
do {
|
|
Instruction *Inst = I; // The instruction to sink.
|
|
|
|
// Predecrement I (if it's not begin) so that it isn't invalidated by
|
|
// sinking.
|
|
ProcessedBegin = I == BB.begin();
|
|
if (!ProcessedBegin)
|
|
--I;
|
|
|
|
if (isa<DbgInfoIntrinsic>(Inst))
|
|
continue;
|
|
|
|
if (SinkInstruction(Inst, Stores))
|
|
++NumSunk, MadeChange = true;
|
|
|
|
// If we just processed the first instruction in the block, we're done.
|
|
} while (!ProcessedBegin);
|
|
|
|
return MadeChange;
|
|
}
|
|
|
|
static bool isSafeToMove(Instruction *Inst, AliasAnalysis *AA,
|
|
SmallPtrSet<Instruction *, 8> &Stores) {
|
|
if (LoadInst *L = dyn_cast<LoadInst>(Inst)) {
|
|
if (L->isVolatile()) return false;
|
|
|
|
Value *Ptr = L->getPointerOperand();
|
|
unsigned Size = AA->getTypeStoreSize(L->getType());
|
|
for (SmallPtrSet<Instruction *, 8>::iterator I = Stores.begin(),
|
|
E = Stores.end(); I != E; ++I)
|
|
if (AA->getModRefInfo(*I, Ptr, Size) & AliasAnalysis::Mod)
|
|
return false;
|
|
}
|
|
|
|
if (Inst->mayWriteToMemory()) {
|
|
Stores.insert(Inst);
|
|
return false;
|
|
}
|
|
|
|
return Inst->isSafeToSpeculativelyExecute();
|
|
}
|
|
|
|
/// SinkInstruction - Determine whether it is safe to sink the specified machine
|
|
/// instruction out of its current block into a successor.
|
|
bool Sinking::SinkInstruction(Instruction *Inst,
|
|
SmallPtrSet<Instruction *, 8> &Stores) {
|
|
// Check if it's safe to move the instruction.
|
|
if (!isSafeToMove(Inst, AA, Stores))
|
|
return false;
|
|
|
|
// FIXME: This should include support for sinking instructions within the
|
|
// block they are currently in to shorten the live ranges. We often get
|
|
// instructions sunk into the top of a large block, but it would be better to
|
|
// also sink them down before their first use in the block. This xform has to
|
|
// be careful not to *increase* register pressure though, e.g. sinking
|
|
// "x = y + z" down if it kills y and z would increase the live ranges of y
|
|
// and z and only shrink the live range of x.
|
|
|
|
// Loop over all the operands of the specified instruction. If there is
|
|
// anything we can't handle, bail out.
|
|
BasicBlock *ParentBlock = Inst->getParent();
|
|
|
|
// SuccToSinkTo - This is the successor to sink this instruction to, once we
|
|
// decide.
|
|
BasicBlock *SuccToSinkTo = 0;
|
|
|
|
// FIXME: This picks a successor to sink into based on having one
|
|
// successor that dominates all the uses. However, there are cases where
|
|
// sinking can happen but where the sink point isn't a successor. For
|
|
// example:
|
|
// x = computation
|
|
// if () {} else {}
|
|
// use x
|
|
// the instruction could be sunk over the whole diamond for the
|
|
// if/then/else (or loop, etc), allowing it to be sunk into other blocks
|
|
// after that.
|
|
|
|
// Instructions can only be sunk if all their uses are in blocks
|
|
// dominated by one of the successors.
|
|
// Look at all the successors and decide which one
|
|
// we should sink to.
|
|
for (succ_iterator SI = succ_begin(ParentBlock),
|
|
E = succ_end(ParentBlock); SI != E; ++SI) {
|
|
if (AllUsesDominatedByBlock(Inst, *SI)) {
|
|
SuccToSinkTo = *SI;
|
|
break;
|
|
}
|
|
}
|
|
|
|
// If we couldn't find a block to sink to, ignore this instruction.
|
|
if (SuccToSinkTo == 0)
|
|
return false;
|
|
|
|
// It is not possible to sink an instruction into its own block. This can
|
|
// happen with loops.
|
|
if (Inst->getParent() == SuccToSinkTo)
|
|
return false;
|
|
|
|
DEBUG(dbgs() << "Sink instr " << *Inst);
|
|
DEBUG(dbgs() << "to block ";
|
|
WriteAsOperand(dbgs(), SuccToSinkTo, false));
|
|
|
|
// If the block has multiple predecessors, this would introduce computation on
|
|
// a path that it doesn't already exist. We could split the critical edge,
|
|
// but for now we just punt.
|
|
// FIXME: Split critical edges if not backedges.
|
|
if (SuccToSinkTo->getUniquePredecessor() != ParentBlock) {
|
|
// We cannot sink a load across a critical edge - there may be stores in
|
|
// other code paths.
|
|
if (!Inst->isSafeToSpeculativelyExecute()) {
|
|
DEBUG(dbgs() << " *** PUNTING: Wont sink load along critical edge.\n");
|
|
return false;
|
|
}
|
|
|
|
// We don't want to sink across a critical edge if we don't dominate the
|
|
// successor. We could be introducing calculations to new code paths.
|
|
if (!DT->dominates(ParentBlock, SuccToSinkTo)) {
|
|
DEBUG(dbgs() << " *** PUNTING: Critical edge found\n");
|
|
return false;
|
|
}
|
|
|
|
// Don't sink instructions into a loop.
|
|
if (LI->isLoopHeader(SuccToSinkTo)) {
|
|
DEBUG(dbgs() << " *** PUNTING: Loop header found\n");
|
|
return false;
|
|
}
|
|
|
|
// Otherwise we are OK with sinking along a critical edge.
|
|
DEBUG(dbgs() << "Sinking along critical edge.\n");
|
|
}
|
|
|
|
// Determine where to insert into. Skip phi nodes.
|
|
BasicBlock::iterator InsertPos = SuccToSinkTo->begin();
|
|
while (InsertPos != SuccToSinkTo->end() && isa<PHINode>(InsertPos))
|
|
++InsertPos;
|
|
|
|
// Move the instruction.
|
|
Inst->moveBefore(InsertPos);
|
|
return true;
|
|
}
|