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// LLVM loop pass that adds required barriers to loops.
//
// Copyright (c) 2011 Universidad Rey Juan Carlos
// 2012-2014 Pekka Jääskeläinen / Tampere University of Technology
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
#include "config.h"
#if (defined LLVM_3_1 or defined LLVM_3_2)
#include "llvm/Constants.h"
#include "llvm/Instructions.h"
#include "llvm/Module.h"
#else
#include "llvm/IR/Constants.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Module.h"
#endif
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include <iostream>
#include "LoopBarriers.h"
#include "Barrier.h"
#include "Workgroup.h"
//#define DEBUG_LOOP_BARRIERS
using namespace llvm;
using namespace pocl;
namespace {
static
RegisterPass<LoopBarriers> X("loop-barriers",
"Add needed barriers to loops");
}
char LoopBarriers::ID = 0;
void
LoopBarriers::getAnalysisUsage(AnalysisUsage &AU) const
{
AU.addRequired<DominatorTree>();
AU.addPreserved<DominatorTree>();
}
bool
LoopBarriers::runOnLoop(Loop *L, LPPassManager &LPM)
{
if (!Workgroup::isKernelToProcess(*L->getHeader()->getParent()))
return false;
DT = &getAnalysis<DominatorTree>();
bool changed = ProcessLoop(L, LPM);
DT->verifyAnalysis();
return changed;
}
bool
LoopBarriers::ProcessLoop(Loop *L, LPPassManager &LPM)
{
bool isBLoop = false;
bool changed = false;
for (Loop::block_iterator i = L->block_begin(), e = L->block_end();
i != e && !isBLoop; ++i) {
for (BasicBlock::iterator j = (*i)->begin(), e = (*i)->end();
j != e; ++j) {
if (isa<Barrier>(j)) {
isBLoop = true;
break;
}
}
}
for (Loop::block_iterator i = L->block_begin(), e = L->block_end();
i != e && isBLoop; ++i) {
for (BasicBlock::iterator j = (*i)->begin(), e = (*i)->end();
j != e; ++j) {
if (isa<Barrier>(j)) {
// Found a barrier in this loop:
// 1) add a barrier in the loop header.
// 2) add a barrier in the latches
// Add a barrier on the preheader to ensure all WIs reach
// the loop header with all the previous code already
// executed.
BasicBlock *preheader = L->getLoopPreheader();
assert((preheader != NULL) && "Non-canonicalized loop found!\n");
#ifdef DEBUG_LOOP_BARRIERS
std::cerr << "### adding to preheader BB" << std::endl;
preheader->dump();
std::cerr << "### before instr" << std::endl;
preheader->getTerminator()->dump();
#endif
Barrier::Create(preheader->getTerminator());
preheader->setName(preheader->getName() + ".loopbarrier");
// Add a barrier after the PHI nodes on the header (the replicated
// headers will be merged afterwards).
BasicBlock *header = L->getHeader();
if (header->getFirstNonPHI() != &header->front()) {
Barrier::Create(header->getFirstNonPHI());
header->setName(header->getName() + ".phibarrier");
// Split the block to create a replicable region of
// the loop contents in case the phi node contains a
// branch (that can be to inside the region).
// if (header->getTerminator()->getNumSuccessors() > 1)
// SplitBlock(header, header->getTerminator(), this);
}
// Add the barriers on the exiting block and the latches,
// which might not always be the same if there is computation
// after the exit decision.
BasicBlock *brexit = L->getExitingBlock();
if (brexit != NULL) {
Barrier::Create(brexit->getTerminator());
brexit->setName(brexit->getName() + ".brexitbarrier");
}
BasicBlock *latch = L->getLoopLatch();
if (latch != NULL && brexit != latch) {
// This loop has only one latch. Do not check for dominance, we
// are probably running before BTR.
Barrier::Create(latch->getTerminator());
latch->setName(latch->getName() + ".latchbarrier");
return changed;
}
// Modified code from llvm::LoopBase::getLoopLatch to
// go trough all the latches.
BasicBlock *Header = L->getHeader();
typedef GraphTraits<Inverse<BasicBlock *> > InvBlockTraits;
InvBlockTraits::ChildIteratorType PI = InvBlockTraits::child_begin(Header);
InvBlockTraits::ChildIteratorType PE = InvBlockTraits::child_end(Header);
BasicBlock *Latch = NULL;
for (; PI != PE; ++PI) {
InvBlockTraits::NodeType *N = *PI;
if (L->contains(N)) {
Latch = N;
// Latch found in the loop, see if the barrier dominates it
// (otherwise if might no even belong to this "tail", see
// forifbarrier1 graph test).
if (DT->dominates(j->getParent(), Latch)) {
Barrier::Create(Latch->getTerminator());
Latch->setName(Latch->getName() + ".latchbarrier");
}
}
}
return true;
}
}
}
/* This is a loop without a barrier. Ensure we have a non-barrier
block as a preheader so we can replicate the loop as a whole.
If the block has proper instructions after the barrier, it
will be split in CanonicalizeBarriers. */
BasicBlock *preheader = L->getLoopPreheader();
assert((preheader != NULL) && "Non-canonicalized loop found!\n");
TerminatorInst *t = preheader->getTerminator();
Instruction *prev = NULL;
if (&preheader->front() != t)
prev = t->getPrevNode();
if (prev && isa<Barrier>(prev))
{
BasicBlock *new_b = SplitBlock(preheader, t, this);
new_b->setName(preheader->getName() + ".postbarrier_dummy");
return true;
}
return changed;
}
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