mirror of
https://github.com/c64scene-ar/llvm-6502.git
synced 2024-08-21 03:29:40 +00:00
Patch contributed by Paolo Invernizzi! git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@16152 91177308-0d34-0410-b5e6-96231b3b80d8
359 lines
14 KiB
C++
359 lines
14 KiB
C++
//===-- LoopUnswitch.cpp - Hoist loop-invariant conditionals in loop ------===//
|
|
//
|
|
// The LLVM Compiler Infrastructure
|
|
//
|
|
// This file was developed by the LLVM research group and is distributed under
|
|
// the University of Illinois Open Source License. See LICENSE.TXT for details.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
//
|
|
// This pass transforms loops that contain branches on loop-invariant conditions
|
|
// to have multiple loops. For example, it turns the left into the right code:
|
|
//
|
|
// for (...) if (lic)
|
|
// A for (...)
|
|
// if (lic) A; B; C
|
|
// B else
|
|
// C for (...)
|
|
// A; C
|
|
//
|
|
// This can increase the size of the code exponentially (doubling it every time
|
|
// a loop is unswitched) so we only unswitch if the resultant code will be
|
|
// smaller than a threshold.
|
|
//
|
|
// This pass expects LICM to be run before it to hoist invariant conditions out
|
|
// of the loop, to make the unswitching opportunity obvious.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
#define DEBUG_TYPE "loop-unswitch"
|
|
#include "llvm/Transforms/Scalar.h"
|
|
#include "llvm/Constants.h"
|
|
#include "llvm/Function.h"
|
|
#include "llvm/Instructions.h"
|
|
#include "llvm/Analysis/Dominators.h"
|
|
#include "llvm/Analysis/LoopInfo.h"
|
|
#include "llvm/Transforms/Utils/Cloning.h"
|
|
#include "llvm/Transforms/Utils/Local.h"
|
|
#include "llvm/Support/Debug.h"
|
|
#include "llvm/ADT/Statistic.h"
|
|
#include <algorithm>
|
|
using namespace llvm;
|
|
|
|
namespace {
|
|
Statistic<> NumUnswitched("loop-unswitch", "Number of loops unswitched");
|
|
|
|
class LoopUnswitch : public FunctionPass {
|
|
LoopInfo *LI; // Loop information
|
|
DominatorSet *DS;
|
|
public:
|
|
virtual bool runOnFunction(Function &F);
|
|
bool visitLoop(Loop *L);
|
|
|
|
/// This transformation requires natural loop information & requires that
|
|
/// loop preheaders be inserted into the CFG...
|
|
///
|
|
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
|
|
AU.addRequiredID(LoopSimplifyID);
|
|
//AU.addRequired<DominatorSet>();
|
|
AU.addRequired<LoopInfo>();
|
|
AU.addPreserved<LoopInfo>();
|
|
}
|
|
|
|
private:
|
|
void VersionLoop(Value *LIC, Loop *L);
|
|
BasicBlock *SplitBlock(BasicBlock *BB, bool SplitAtTop);
|
|
void RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC, bool Val);
|
|
};
|
|
RegisterOpt<LoopUnswitch> X("loop-unswitch", "Unswitch loops");
|
|
}
|
|
|
|
FunctionPass *createLoopUnswitchPass() { return new LoopUnswitch(); }
|
|
|
|
bool LoopUnswitch::runOnFunction(Function &F) {
|
|
bool Changed = false;
|
|
LI = &getAnalysis<LoopInfo>();
|
|
DS = 0; //&getAnalysis<DominatorSet>();
|
|
|
|
// Transform all the top-level loops. Copy the loop list so that the child
|
|
// can update the loop tree if it needs to delete the loop.
|
|
std::vector<Loop*> SubLoops(LI->begin(), LI->end());
|
|
for (unsigned i = 0, e = SubLoops.size(); i != e; ++i)
|
|
Changed |= visitLoop(SubLoops[i]);
|
|
|
|
return Changed;
|
|
}
|
|
|
|
bool LoopUnswitch::visitLoop(Loop *L) {
|
|
bool Changed = false;
|
|
|
|
// Recurse through all subloops before we process this loop. Copy the loop
|
|
// list so that the child can update the loop tree if it needs to delete the
|
|
// loop.
|
|
std::vector<Loop*> SubLoops(L->begin(), L->end());
|
|
for (unsigned i = 0, e = SubLoops.size(); i != e; ++i)
|
|
Changed |= visitLoop(SubLoops[i]);
|
|
|
|
// Loop over all of the basic blocks in the loop. If we find an interior
|
|
// block that is branching on a loop-invariant condition, we can unswitch this
|
|
// loop.
|
|
for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
|
|
I != E; ++I) {
|
|
TerminatorInst *TI = (*I)->getTerminator();
|
|
if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
|
|
if (!isa<Constant>(SI) && L->isLoopInvariant(SI->getCondition()))
|
|
DEBUG(std::cerr << "Can't unswitching 'switch' loop %"
|
|
<< L->getHeader()->getName() << ", cost = "
|
|
<< L->getBlocks().size() << "\n" << **I);
|
|
} else if (BranchInst *BI = dyn_cast<BranchInst>(TI))
|
|
if (BI->isConditional() && !isa<Constant>(BI->getCondition()) &&
|
|
L->isLoopInvariant(BI->getCondition())) {
|
|
// Check to see if it would be profitable to unswitch this loop.
|
|
if (L->getBlocks().size() > 10) {
|
|
DEBUG(std::cerr << "NOT unswitching loop %"
|
|
<< L->getHeader()->getName() << ", cost too high: "
|
|
<< L->getBlocks().size() << "\n");
|
|
} else {
|
|
// FIXME: check for profitability.
|
|
//std::cerr << "BEFORE:\n"; LI->dump();
|
|
|
|
VersionLoop(BI->getCondition(), L);
|
|
|
|
//std::cerr << "AFTER:\n"; LI->dump();
|
|
return true;
|
|
}
|
|
}
|
|
}
|
|
|
|
return Changed;
|
|
}
|
|
|
|
/// SplitBlock - Split the specified basic block into two pieces. If SplitAtTop
|
|
/// is false, this splits the block so the second half only has an unconditional
|
|
/// branch. If SplitAtTop is true, it makes it so the first half of the block
|
|
/// only has an unconditional branch in it.
|
|
///
|
|
/// This method updates the LoopInfo for this function to correctly reflect the
|
|
/// CFG changes made.
|
|
BasicBlock *LoopUnswitch::SplitBlock(BasicBlock *BB, bool SplitAtTop) {
|
|
BasicBlock::iterator SplitPoint;
|
|
if (!SplitAtTop)
|
|
SplitPoint = BB->getTerminator();
|
|
else {
|
|
SplitPoint = BB->begin();
|
|
while (isa<PHINode>(SplitPoint)) ++SplitPoint;
|
|
}
|
|
|
|
BasicBlock *New = BB->splitBasicBlock(SplitPoint, BB->getName()+".tail");
|
|
// New now lives in whichever loop that BB used to.
|
|
if (Loop *L = LI->getLoopFor(BB))
|
|
L->addBasicBlockToLoop(New, *LI);
|
|
return SplitAtTop ? BB : New;
|
|
}
|
|
|
|
|
|
// RemapInstruction - Convert the instruction operands from referencing the
|
|
// current values into those specified by ValueMap.
|
|
//
|
|
static inline void RemapInstruction(Instruction *I,
|
|
std::map<const Value *, Value*> &ValueMap) {
|
|
for (unsigned op = 0, E = I->getNumOperands(); op != E; ++op) {
|
|
Value *Op = I->getOperand(op);
|
|
std::map<const Value *, Value*>::iterator It = ValueMap.find(Op);
|
|
if (It != ValueMap.end()) Op = It->second;
|
|
I->setOperand(op, Op);
|
|
}
|
|
}
|
|
|
|
/// CloneLoop - Recursively clone the specified loop and all of its children,
|
|
/// mapping the blocks with the specified map.
|
|
static Loop *CloneLoop(Loop *L, Loop *PL, std::map<const Value*, Value*> &VM,
|
|
LoopInfo *LI) {
|
|
Loop *New = new Loop();
|
|
|
|
if (PL)
|
|
PL->addChildLoop(New);
|
|
else
|
|
LI->addTopLevelLoop(New);
|
|
|
|
// Add all of the blocks in L to the new loop.
|
|
for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
|
|
I != E; ++I)
|
|
if (LI->getLoopFor(*I) == L)
|
|
New->addBasicBlockToLoop(cast<BasicBlock>(VM[*I]), *LI);
|
|
|
|
// Add all of the subloops to the new loop.
|
|
for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I)
|
|
CloneLoop(*I, New, VM, LI);
|
|
|
|
return New;
|
|
}
|
|
|
|
|
|
/// InsertPHINodesForUsesOutsideLoop - If this instruction is used outside of
|
|
/// the specified loop, insert a PHI node in the appropriate exit block to merge
|
|
/// the values in the two different loop versions.
|
|
///
|
|
/// Most values are not used outside of the loop they are defined in, so be
|
|
/// efficient for this case.
|
|
///
|
|
static AllocaInst *
|
|
InsertPHINodesForUsesOutsideLoop(Instruction *OI, Instruction *NI,
|
|
DominatorSet &DS, Loop *OL, Loop *NL,
|
|
std::vector<BasicBlock*> &OldExitBlocks,
|
|
std::map<const Value*, Value*> &ValueMap) {
|
|
assert(OI->getType() == NI->getType() && OI->getOpcode() == NI->getOpcode() &&
|
|
"Hrm, should be mapping between identical instructions!");
|
|
for (Value::use_iterator UI = OI->use_begin(), E = OI->use_end(); UI != E;
|
|
++UI)
|
|
if (!OL->contains(cast<Instruction>(*UI)->getParent()) &&
|
|
!NL->contains(cast<Instruction>(*UI)->getParent()))
|
|
goto UsedOutsideOfLoop;
|
|
return 0;
|
|
|
|
UsedOutsideOfLoop:
|
|
// Okay, this instruction is used outside of the current loop. Insert a PHI
|
|
// nodes for the instruction merging the values together.
|
|
|
|
// FIXME: For now we just spill the object to the stack, assuming that a
|
|
// subsequent mem2reg pass will clean up after us. This should be improved in
|
|
// two ways:
|
|
// 1. If there is only one exit block, trivially insert the PHI nodes
|
|
// 2. Once we update domfrontier, we should do the promotion after everything
|
|
// is stable again.
|
|
AllocaInst *Result = DemoteRegToStack(*OI);
|
|
|
|
// Store to the stack location right after the new instruction.
|
|
BasicBlock::iterator InsertPoint = NI;
|
|
if (InvokeInst *II = dyn_cast<InvokeInst>(NI))
|
|
InsertPoint = II->getNormalDest()->begin();
|
|
else
|
|
++InsertPoint;
|
|
while (isa<PHINode>(InsertPoint)) ++InsertPoint;
|
|
new StoreInst(NI, Result, InsertPoint);
|
|
return Result;
|
|
}
|
|
|
|
|
|
|
|
/// VersionLoop - We determined that the loop is profitable to unswitch and
|
|
/// contains a branch on a loop invariant condition. Split it into loop
|
|
/// versions and test the condition outside of either loop.
|
|
void LoopUnswitch::VersionLoop(Value *LIC, Loop *L) {
|
|
Function *F = L->getHeader()->getParent();
|
|
|
|
DEBUG(std::cerr << "loop-unswitch: Unswitching loop %"
|
|
<< L->getHeader()->getName() << " [" << L->getBlocks().size()
|
|
<< " blocks] in Function " << F->getName()
|
|
<< " on cond:" << *LIC << "\n");
|
|
|
|
std::vector<BasicBlock*> LoopBlocks;
|
|
|
|
// First step, split the preheader and exit blocks, and add these blocks to
|
|
// the LoopBlocks list.
|
|
BasicBlock *OrigPreheader = L->getLoopPreheader();
|
|
LoopBlocks.push_back(SplitBlock(OrigPreheader, false));
|
|
|
|
// We want the loop to come after the preheader, but before the exit blocks.
|
|
LoopBlocks.insert(LoopBlocks.end(), L->block_begin(), L->block_end());
|
|
|
|
std::vector<BasicBlock*> ExitBlocks;
|
|
L->getExitBlocks(ExitBlocks);
|
|
std::sort(ExitBlocks.begin(), ExitBlocks.end());
|
|
ExitBlocks.erase(std::unique(ExitBlocks.begin(), ExitBlocks.end()),
|
|
ExitBlocks.end());
|
|
for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
|
|
LoopBlocks.push_back(ExitBlocks[i] = SplitBlock(ExitBlocks[i], true));
|
|
|
|
// Next step, clone all of the basic blocks that make up the loop (including
|
|
// the loop preheader and exit blocks), keeping track of the mapping between
|
|
// the instructions and blocks.
|
|
std::vector<BasicBlock*> NewBlocks;
|
|
NewBlocks.reserve(LoopBlocks.size());
|
|
std::map<const Value*, Value*> ValueMap;
|
|
for (unsigned i = 0, e = LoopBlocks.size(); i != e; ++i) {
|
|
NewBlocks.push_back(CloneBasicBlock(LoopBlocks[i], ValueMap, ".us", F));
|
|
ValueMap[LoopBlocks[i]] = NewBlocks.back(); // Keep the BB mapping.
|
|
}
|
|
|
|
// Splice the newly inserted blocks into the function right before the
|
|
// original preheader.
|
|
F->getBasicBlockList().splice(LoopBlocks[0], F->getBasicBlockList(),
|
|
NewBlocks[0], F->end());
|
|
|
|
// Now we create the new Loop object for the versioned loop.
|
|
Loop *NewLoop = CloneLoop(L, L->getParentLoop(), ValueMap, LI);
|
|
if (Loop *Parent = L->getParentLoop()) {
|
|
// Make sure to add the cloned preheader and exit blocks to the parent loop
|
|
// as well.
|
|
Parent->addBasicBlockToLoop(NewBlocks[0], *LI);
|
|
for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
|
|
Parent->addBasicBlockToLoop(cast<BasicBlock>(ValueMap[ExitBlocks[i]]),
|
|
*LI);
|
|
}
|
|
|
|
// Rewrite the code to refer to itself.
|
|
for (unsigned i = 0, e = NewBlocks.size(); i != e; ++i)
|
|
for (BasicBlock::iterator I = NewBlocks[i]->begin(),
|
|
E = NewBlocks[i]->end(); I != E; ++I)
|
|
RemapInstruction(I, ValueMap);
|
|
|
|
// If the instructions are used outside of the loop, insert a PHI node in any
|
|
// exit blocks dominated by the instruction.
|
|
for (unsigned i = 0, e = NewBlocks.size(); i != e; ++i)
|
|
for (BasicBlock::iterator OI = LoopBlocks[i]->begin(),
|
|
E = LoopBlocks[i]->end(); OI != E; ++OI)
|
|
if (!OI->use_empty()) {
|
|
std::map<const Value*,Value*>::iterator OII = ValueMap.find(OI);
|
|
// The PHINode rewriting stuff can insert stores that are not in the
|
|
// mapping. Don't mess around with them.
|
|
if (OII != ValueMap.end()) {
|
|
Instruction *NI = cast<Instruction>(OII->second);
|
|
InsertPHINodesForUsesOutsideLoop(OI, NI, *DS, L, NewLoop,
|
|
ExitBlocks, ValueMap);
|
|
}
|
|
}
|
|
|
|
// Rewrite the original preheader to select between versions of the loop.
|
|
assert(isa<BranchInst>(OrigPreheader->getTerminator()) &&
|
|
cast<BranchInst>(OrigPreheader->getTerminator())->isUnconditional() &&
|
|
OrigPreheader->getTerminator()->getSuccessor(0) == LoopBlocks[0] &&
|
|
"Preheader splitting did not work correctly!");
|
|
// Remove the unconditional branch to LoopBlocks[0].
|
|
OrigPreheader->getInstList().pop_back();
|
|
|
|
// Insert a conditional branch on LIC to the two preheaders. The original
|
|
// code is the true version and the new code is the false version.
|
|
new BranchInst(LoopBlocks[0], NewBlocks[0], LIC, OrigPreheader);
|
|
|
|
// Now we rewrite the original code to know that the condition is true and the
|
|
// new code to know that the condition is false.
|
|
RewriteLoopBodyWithConditionConstant(L, LIC, true);
|
|
RewriteLoopBodyWithConditionConstant(NewLoop, LIC, false);
|
|
++NumUnswitched;
|
|
|
|
// Try to unswitch each of our new loops now!
|
|
visitLoop(L);
|
|
visitLoop(NewLoop);
|
|
}
|
|
|
|
// RewriteLoopBodyWithConditionConstant - We know that the boolean value LIC has
|
|
// the value specified by Val in the specified loop. Rewrite any uses of LIC or
|
|
// of properties correlated to it.
|
|
void LoopUnswitch::RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,
|
|
bool Val) {
|
|
// FIXME: Support correlated properties, like:
|
|
// for (...)
|
|
// if (li1 < li2)
|
|
// ...
|
|
// if (li1 > li2)
|
|
// ...
|
|
ConstantBool *BoolVal = ConstantBool::get(Val);
|
|
|
|
std::vector<User*> Users(LIC->use_begin(), LIC->use_end());
|
|
for (unsigned i = 0, e = Users.size(); i != e; ++i)
|
|
if (Instruction *U = dyn_cast<Instruction>(Users[i]))
|
|
if (L->contains(U->getParent()))
|
|
U->replaceUsesOfWith(LIC, BoolVal);
|
|
}
|