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// LLVM function pass that adds implicit barriers to branches where it sees
// beneficial (and legal).
//
// Copyright (c) 2013 Pekka Jääskeläinen / TUT
//
// 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 "CompilerWarnings.h"
IGNORE_COMPILER_WARNING("-Wmaybe-uninitialized")
#include <llvm/Analysis/PostDominators.h>
#include <llvm/IR/Constants.h>
#include <llvm/IR/Instructions.h>
#include <llvm/IR/Module.h>
#include <llvm/Transforms/Utils/BasicBlockUtils.h>
#include "Barrier.h"
#include "ImplicitConditionalBarriers.h"
#include "LLVMUtils.h"
#include "VariableUniformityAnalysis.h"
#include "VariableUniformityAnalysisResult.hh"
#include "Workgroup.h"
#include "WorkitemHandlerChooser.h"
POP_COMPILER_DIAGS
#include <iostream>
#include "pocl.h"
//#define DEBUG_COND_BARRIERS
#define PASS_NAME "implicit-cond-barriers"
#define PASS_CLASS pocl::ImplicitConditionalBarriers
#define PASS_DESC "Adds implicit barriers to branches."
namespace pocl {
using namespace llvm;
/**
* Finds a predecessor that does not come from a back edge.
*
* This is used to include loops in the conditional parallel region.
*/
static BasicBlock *firstNonBackedgePredecessor(llvm::BasicBlock *BB,
DominatorTree &DT) {
pred_iterator I = pred_begin(BB), E = pred_end(BB);
if (I == E)
return NULL;
while (DT.dominates(BB, *I) && I != E)
++I;
if (I == E)
return NULL;
else
return *I;
}
static bool implicitConditionalBarriers(Function &F,
llvm::PostDominatorTree &PDT,
llvm::DominatorTree &DT) {
typedef std::vector<BasicBlock*> BarrierBlockIndex;
BarrierBlockIndex ConditionalBarriers;
// Required hack. See the docs of removeUnreachableSwitchCases
DT.reset();
PDT.reset();
removeUnreachableSwitchCases(F);
DT.recalculate(F);
PDT.recalculate(F);
for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) {
BasicBlock *BB = &*FI;
if (!Barrier::hasBarrier(BB)) continue;
// Unconditional barrier postdominates the entry node.
if (PDT.dominates(BB, &F.getEntryBlock()))
continue;
#ifdef DEBUG_COND_BARRIERS
std::cerr << "### found a conditional barrier:\n";
BB->dump();
#endif
ConditionalBarriers.push_back(BB);
}
if (ConditionalBarriers.size() == 0)
return true;
for (BarrierBlockIndex::const_iterator i = ConditionalBarriers.begin();
i != ConditionalBarriers.end(); ++i) {
BasicBlock *BB = *i;
// Trace upwards from the barrier until one encounters another
// barrier or the split point that makes the barrier conditional.
// In case of the latter, add a new barrier to both branches of the split point.
// BB before which to inject the barrier.
BasicBlock *Pos = BB;
if (pred_begin(BB) == pred_end(BB)) {
#ifdef DEBUG_COND_BARRIERS
std::cerr << "BB before which to inject the barrier:\n";
BB->dump();
#endif
assert (pred_begin(BB) == pred_end(BB));
}
BasicBlock *Pred = firstNonBackedgePredecessor(BB, DT);
while (!Barrier::hasOnlyBarrier(Pred) && PDT.dominates(BB, Pred)) {
#ifdef DEBUG_COND_BARRIERS
std::cerr << "### looking at BB " << Pred->getName().str() << std::endl;
#endif
Pos = Pred;
// If our BB post dominates the given block, we know it is not the
// branching block that makes the barrier conditional.
Pred = firstNonBackedgePredecessor(Pred, DT);
if (Pred == BB) break; // Traced across a loop edge, skip this case.
}
if (Barrier::hasOnlyBarrier(Pos)) continue;
// Inject a barrier at the beginning of the BB and let the
// CanonicalizeBarrier to clean it up (split to a separate BB).
// mri-q of parboil breaks in case injected at the beginning
// TODO: investigate. It might related to the alloca-converted
// PHIs. It has a loop that is autoconverted to a b-loop and the
// conditional barrier is inserted after the loop short cut check.
Barrier::Create(Pos->getFirstNonPHI());
#ifdef DEBUG_COND_BARRIERS
std::cerr << "### added an implicit barrier to the BB" << std::endl;
Pos->dump();
#endif
}
return true;
}
#if LLVM_MAJOR < MIN_LLVM_NEW_PASSMANAGER
char ImplicitConditionalBarriers::ID = 0;
bool ImplicitConditionalBarriers::runOnFunction(Function &F) {
if (!pocl::isKernelToProcess(F))
return false;
if (!pocl::hasWorkgroupBarriers(F))
return false;
auto WIH = getAnalysis<WorkitemHandlerChooser>().chosenHandler();
if (WIH == WorkitemHandlerType::CBS)
return false;
llvm::PostDominatorTree &PDT =
getAnalysis<PostDominatorTreeWrapperPass>().getPostDomTree();
llvm::DominatorTree &DT =
getAnalysis<DominatorTreeWrapperPass>().getDomTree();
return implicitConditionalBarriers(F, PDT, DT);
}
void ImplicitConditionalBarriers::getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<PostDominatorTreeWrapperPass>();
AU.addRequired<DominatorTreeWrapperPass>();
AU.addPreserved<VariableUniformityAnalysis>();
AU.addRequired<WorkitemHandlerChooser>();
AU.addPreserved<WorkitemHandlerChooser>();
}
REGISTER_OLD_FPASS(PASS_NAME, PASS_CLASS, PASS_DESC);
#else
llvm::PreservedAnalyses
ImplicitConditionalBarriers::run(llvm::Function &F,
llvm::FunctionAnalysisManager &FAM) {
if (!isKernelToProcess(F))
return PreservedAnalyses::all();
if (!hasWorkgroupBarriers(F))
return PreservedAnalyses::all();
WorkitemHandlerType WIH = FAM.getResult<WorkitemHandlerChooser>(F).WIH;
if (WIH == WorkitemHandlerType::CBS)
return PreservedAnalyses::all();
llvm::PostDominatorTree &PDT = FAM.getResult<PostDominatorTreeAnalysis>(F);
llvm::DominatorTree &DT = FAM.getResult<DominatorTreeAnalysis>(F);
PreservedAnalyses PAChanged = PreservedAnalyses::none();
PAChanged.preserve<VariableUniformityAnalysis>();
PAChanged.preserve<WorkitemHandlerChooser>();
return implicitConditionalBarriers(F, PDT, DT) ? PAChanged
: PreservedAnalyses::all();
}
REGISTER_NEW_FPASS(PASS_NAME, PASS_CLASS, PASS_DESC);
#endif
} // namespace pocl
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