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//===--- Utils.cpp - Utility functions for the code generation --*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file contains utility functions for the code generation.
//
//===----------------------------------------------------------------------===//
#include "polly/CodeGen/Utils.h"
#include "polly/CodeGen/IRBuilder.h"
#include "polly/ScopInfo.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/RegionInfo.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
using namespace llvm;
// Alternative to llvm::SplitCriticalEdge.
//
// Creates a new block which branches to Succ. The edge to split is redirected
// to the new block.
//
// The issue with llvm::SplitCriticalEdge is that it does nothing if the edge is
// not critical.
// The issue with llvm::SplitEdge is that it does not always create the middle
// block, but reuses Prev/Succ if it can. We always want a new middle block.
static BasicBlock *splitEdge(BasicBlock *Prev, BasicBlock *Succ,
const char *Suffix, DominatorTree *DT,
LoopInfo *LI, RegionInfo *RI) {
assert(Prev && Succ);
// Before:
// \ / / //
// Prev / //
// | \___/ //
// | ___ //
// | / \ //
// Succ \ //
// / \ \ //
// The algorithm to update DominatorTree and LoopInfo of
// llvm::SplitCriticalEdge is more efficient than
// llvm::SplitBlockPredecessors, which is more general. In the future we might
// either modify llvm::SplitCriticalEdge to allow skipping the critical edge
// check; or Copy&Pase it here.
BasicBlock *MiddleBlock = SplitBlockPredecessors(
Succ, ArrayRef<BasicBlock *>(Prev), Suffix, DT, LI);
if (RI) {
Region *PrevRegion = RI->getRegionFor(Prev);
Region *SuccRegion = RI->getRegionFor(Succ);
if (PrevRegion->contains(MiddleBlock)) {
RI->setRegionFor(MiddleBlock, PrevRegion);
} else {
RI->setRegionFor(MiddleBlock, SuccRegion);
}
}
// After:
// \ / / //
// Prev / //
// | \___/ //
// | //
// MiddleBlock //
// | ___ //
// | / \ //
// Succ \ //
// / \ \ //
return MiddleBlock;
}
std::pair<polly::BBPair, BranchInst *>
polly::executeScopConditionally(Scop &S, Value *RTC, DominatorTree &DT,
RegionInfo &RI, LoopInfo &LI) {
Region &R = S.getRegion();
PollyIRBuilder Builder(S.getEntry());
// Before:
//
// \ / //
// EnteringBB //
// _____|_____ //
// / EntryBB \ //
// | (region) | //
// \_ExitingBB_/ //
// | //
// ExitBB //
// / \ //
// Create a fork block.
BasicBlock *EnteringBB = S.getEnteringBlock();
BasicBlock *EntryBB = S.getEntry();
assert(EnteringBB && "Must be a simple region");
BasicBlock *SplitBlock =
splitEdge(EnteringBB, EntryBB, ".split_new_and_old", &DT, &LI, &RI);
SplitBlock->setName("polly.split_new_and_old");
// If EntryBB is the exit block of the region that includes Prev, exclude
// SplitBlock from that region by making it itself the exit block. This is
// trivially possible because there is just one edge to EnteringBB.
// This is necessary because we will add an outgoing edge from SplitBlock,
// which would violate the single exit block requirement of PrevRegion.
Region *PrevRegion = RI.getRegionFor(EnteringBB);
while (PrevRegion->getExit() == EntryBB) {
PrevRegion->replaceExit(SplitBlock);
PrevRegion = PrevRegion->getParent();
}
RI.setRegionFor(SplitBlock, PrevRegion);
// Create a join block
BasicBlock *ExitingBB = S.getExitingBlock();
BasicBlock *ExitBB = S.getExit();
assert(ExitingBB && "Must be a simple region");
BasicBlock *MergeBlock =
splitEdge(ExitingBB, ExitBB, ".merge_new_and_old", &DT, &LI, &RI);
MergeBlock->setName("polly.merge_new_and_old");
// Exclude the join block from the region.
R.replaceExitRecursive(MergeBlock);
RI.setRegionFor(MergeBlock, R.getParent());
// \ / //
// EnteringBB //
// | //
// SplitBlock //
// _____|_____ //
// / EntryBB \ //
// | (region) | //
// \_ExitingBB_/ //
// | //
// MergeBlock //
// | //
// ExitBB //
// / \ //
// Create the start and exiting block.
Function *F = SplitBlock->getParent();
BasicBlock *StartBlock =
BasicBlock::Create(F->getContext(), "polly.start", F);
BasicBlock *ExitingBlock =
BasicBlock::Create(F->getContext(), "polly.exiting", F);
SplitBlock->getTerminator()->eraseFromParent();
Builder.SetInsertPoint(SplitBlock);
BranchInst *CondBr = Builder.CreateCondBr(RTC, StartBlock, S.getEntry());
if (Loop *L = LI.getLoopFor(SplitBlock)) {
L->addBasicBlockToLoop(StartBlock, LI);
L->addBasicBlockToLoop(ExitingBlock, LI);
}
DT.addNewBlock(StartBlock, SplitBlock);
DT.addNewBlock(ExitingBlock, StartBlock);
RI.setRegionFor(StartBlock, RI.getRegionFor(SplitBlock));
RI.setRegionFor(ExitingBlock, RI.getRegionFor(SplitBlock));
// \ / //
// EnteringBB //
// | //
// SplitBlock---------\ //
// _____|_____ | //
// / EntryBB \ StartBlock //
// | (region) | | //
// \_ExitingBB_/ ExitingBlock //
// | //
// MergeBlock //
// | //
// ExitBB //
// / \ //
// Connect start block to exiting block.
Builder.SetInsertPoint(StartBlock);
Builder.CreateBr(ExitingBlock);
DT.changeImmediateDominator(ExitingBlock, StartBlock);
// Connect exiting block to join block.
Builder.SetInsertPoint(ExitingBlock);
Builder.CreateBr(MergeBlock);
DT.changeImmediateDominator(MergeBlock, SplitBlock);
// \ / //
// EnteringBB //
// | //
// SplitBlock---------\ //
// _____|_____ | //
// / EntryBB \ StartBlock //
// | (region) | | //
// \_ExitingBB_/ ExitingBlock //
// | | //
// MergeBlock---------/ //
// | //
// ExitBB //
// / \ //
//
// Split the edge between SplitBlock and EntryBB, to avoid a critical edge.
splitEdge(SplitBlock, EntryBB, ".pre_entry_bb", &DT, &LI, &RI);
// \ / //
// EnteringBB //
// | //
// SplitBlock---------\ //
// | | //
// PreEntryBB | //
// _____|_____ | //
// / EntryBB \ StartBlock //
// | (region) | | //
// \_ExitingBB_/ ExitingBlock //
// | | //
// MergeBlock---------/ //
// | //
// ExitBB //
// / \ //
return std::make_pair(std::make_pair(StartBlock, ExitingBlock), CondBr);
}
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