You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
679 lines
28 KiB
679 lines
28 KiB
//===-- UnrollLoopRuntime.cpp - Runtime Loop unrolling utilities ----------===//
|
|
//
|
|
// The LLVM Compiler Infrastructure
|
|
//
|
|
// This file is distributed under the University of Illinois Open Source
|
|
// License. See LICENSE.TXT for details.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
//
|
|
// This file implements some loop unrolling utilities for loops with run-time
|
|
// trip counts. See LoopUnroll.cpp for unrolling loops with compile-time
|
|
// trip counts.
|
|
//
|
|
// The functions in this file are used to generate extra code when the
|
|
// run-time trip count modulo the unroll factor is not 0. When this is the
|
|
// case, we need to generate code to execute these 'left over' iterations.
|
|
//
|
|
// The current strategy generates an if-then-else sequence prior to the
|
|
// unrolled loop to execute the 'left over' iterations before or after the
|
|
// unrolled loop.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
#include "llvm/Transforms/Utils/UnrollLoop.h"
|
|
#include "llvm/ADT/Statistic.h"
|
|
#include "llvm/Analysis/AliasAnalysis.h"
|
|
#include "llvm/Analysis/LoopIterator.h"
|
|
#include "llvm/Analysis/LoopPass.h"
|
|
#include "llvm/Analysis/ScalarEvolution.h"
|
|
#include "llvm/Analysis/ScalarEvolutionExpander.h"
|
|
#include "llvm/IR/BasicBlock.h"
|
|
#include "llvm/IR/Dominators.h"
|
|
#include "llvm/IR/Metadata.h"
|
|
#include "llvm/IR/Module.h"
|
|
#include "llvm/Support/Debug.h"
|
|
#include "llvm/Support/raw_ostream.h"
|
|
#include "llvm/Transforms/Scalar.h"
|
|
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
|
|
#include "llvm/Transforms/Utils/Cloning.h"
|
|
#include <algorithm>
|
|
|
|
using namespace llvm;
|
|
|
|
#define DEBUG_TYPE "loop-unroll"
|
|
|
|
STATISTIC(NumRuntimeUnrolled,
|
|
"Number of loops unrolled with run-time trip counts");
|
|
|
|
/// Connect the unrolling prolog code to the original loop.
|
|
/// The unrolling prolog code contains code to execute the
|
|
/// 'extra' iterations if the run-time trip count modulo the
|
|
/// unroll count is non-zero.
|
|
///
|
|
/// This function performs the following:
|
|
/// - Create PHI nodes at prolog end block to combine values
|
|
/// that exit the prolog code and jump around the prolog.
|
|
/// - Add a PHI operand to a PHI node at the loop exit block
|
|
/// for values that exit the prolog and go around the loop.
|
|
/// - Branch around the original loop if the trip count is less
|
|
/// than the unroll factor.
|
|
///
|
|
static void ConnectProlog(Loop *L, Value *BECount, unsigned Count,
|
|
BasicBlock *PrologExit, BasicBlock *PreHeader,
|
|
BasicBlock *NewPreHeader, ValueToValueMapTy &VMap,
|
|
DominatorTree *DT, LoopInfo *LI, bool PreserveLCSSA) {
|
|
BasicBlock *Latch = L->getLoopLatch();
|
|
assert(Latch && "Loop must have a latch");
|
|
BasicBlock *PrologLatch = cast<BasicBlock>(VMap[Latch]);
|
|
|
|
// Create a PHI node for each outgoing value from the original loop
|
|
// (which means it is an outgoing value from the prolog code too).
|
|
// The new PHI node is inserted in the prolog end basic block.
|
|
// The new PHI node value is added as an operand of a PHI node in either
|
|
// the loop header or the loop exit block.
|
|
for (BasicBlock *Succ : successors(Latch)) {
|
|
for (Instruction &BBI : *Succ) {
|
|
PHINode *PN = dyn_cast<PHINode>(&BBI);
|
|
// Exit when we passed all PHI nodes.
|
|
if (!PN)
|
|
break;
|
|
// Add a new PHI node to the prolog end block and add the
|
|
// appropriate incoming values.
|
|
PHINode *NewPN = PHINode::Create(PN->getType(), 2, PN->getName() + ".unr",
|
|
PrologExit->getFirstNonPHI());
|
|
// Adding a value to the new PHI node from the original loop preheader.
|
|
// This is the value that skips all the prolog code.
|
|
if (L->contains(PN)) {
|
|
NewPN->addIncoming(PN->getIncomingValueForBlock(NewPreHeader),
|
|
PreHeader);
|
|
} else {
|
|
NewPN->addIncoming(UndefValue::get(PN->getType()), PreHeader);
|
|
}
|
|
|
|
Value *V = PN->getIncomingValueForBlock(Latch);
|
|
if (Instruction *I = dyn_cast<Instruction>(V)) {
|
|
if (L->contains(I)) {
|
|
V = VMap.lookup(I);
|
|
}
|
|
}
|
|
// Adding a value to the new PHI node from the last prolog block
|
|
// that was created.
|
|
NewPN->addIncoming(V, PrologLatch);
|
|
|
|
// Update the existing PHI node operand with the value from the
|
|
// new PHI node. How this is done depends on if the existing
|
|
// PHI node is in the original loop block, or the exit block.
|
|
if (L->contains(PN)) {
|
|
PN->setIncomingValue(PN->getBasicBlockIndex(NewPreHeader), NewPN);
|
|
} else {
|
|
PN->addIncoming(NewPN, PrologExit);
|
|
}
|
|
}
|
|
}
|
|
|
|
// Create a branch around the original loop, which is taken if there are no
|
|
// iterations remaining to be executed after running the prologue.
|
|
Instruction *InsertPt = PrologExit->getTerminator();
|
|
IRBuilder<> B(InsertPt);
|
|
|
|
assert(Count != 0 && "nonsensical Count!");
|
|
|
|
// If BECount <u (Count - 1) then (BECount + 1) % Count == (BECount + 1)
|
|
// This means %xtraiter is (BECount + 1) and all of the iterations of this
|
|
// loop were executed by the prologue. Note that if BECount <u (Count - 1)
|
|
// then (BECount + 1) cannot unsigned-overflow.
|
|
Value *BrLoopExit =
|
|
B.CreateICmpULT(BECount, ConstantInt::get(BECount->getType(), Count - 1));
|
|
BasicBlock *Exit = L->getUniqueExitBlock();
|
|
assert(Exit && "Loop must have a single exit block only");
|
|
// Split the exit to maintain loop canonicalization guarantees
|
|
SmallVector<BasicBlock*, 4> Preds(predecessors(Exit));
|
|
SplitBlockPredecessors(Exit, Preds, ".unr-lcssa", DT, LI,
|
|
PreserveLCSSA);
|
|
// Add the branch to the exit block (around the unrolled loop)
|
|
B.CreateCondBr(BrLoopExit, Exit, NewPreHeader);
|
|
InsertPt->eraseFromParent();
|
|
}
|
|
|
|
/// Connect the unrolling epilog code to the original loop.
|
|
/// The unrolling epilog code contains code to execute the
|
|
/// 'extra' iterations if the run-time trip count modulo the
|
|
/// unroll count is non-zero.
|
|
///
|
|
/// This function performs the following:
|
|
/// - Update PHI nodes at the unrolling loop exit and epilog loop exit
|
|
/// - Create PHI nodes at the unrolling loop exit to combine
|
|
/// values that exit the unrolling loop code and jump around it.
|
|
/// - Update PHI operands in the epilog loop by the new PHI nodes
|
|
/// - Branch around the epilog loop if extra iters (ModVal) is zero.
|
|
///
|
|
static void ConnectEpilog(Loop *L, Value *ModVal, BasicBlock *NewExit,
|
|
BasicBlock *Exit, BasicBlock *PreHeader,
|
|
BasicBlock *EpilogPreHeader, BasicBlock *NewPreHeader,
|
|
ValueToValueMapTy &VMap, DominatorTree *DT,
|
|
LoopInfo *LI, bool PreserveLCSSA) {
|
|
BasicBlock *Latch = L->getLoopLatch();
|
|
assert(Latch && "Loop must have a latch");
|
|
BasicBlock *EpilogLatch = cast<BasicBlock>(VMap[Latch]);
|
|
|
|
// Loop structure should be the following:
|
|
//
|
|
// PreHeader
|
|
// NewPreHeader
|
|
// Header
|
|
// ...
|
|
// Latch
|
|
// NewExit (PN)
|
|
// EpilogPreHeader
|
|
// EpilogHeader
|
|
// ...
|
|
// EpilogLatch
|
|
// Exit (EpilogPN)
|
|
|
|
// Update PHI nodes at NewExit and Exit.
|
|
for (Instruction &BBI : *NewExit) {
|
|
PHINode *PN = dyn_cast<PHINode>(&BBI);
|
|
// Exit when we passed all PHI nodes.
|
|
if (!PN)
|
|
break;
|
|
// PN should be used in another PHI located in Exit block as
|
|
// Exit was split by SplitBlockPredecessors into Exit and NewExit
|
|
// Basicaly it should look like:
|
|
// NewExit:
|
|
// PN = PHI [I, Latch]
|
|
// ...
|
|
// Exit:
|
|
// EpilogPN = PHI [PN, EpilogPreHeader]
|
|
//
|
|
// There is EpilogPreHeader incoming block instead of NewExit as
|
|
// NewExit was spilt 1 more time to get EpilogPreHeader.
|
|
assert(PN->hasOneUse() && "The phi should have 1 use");
|
|
PHINode *EpilogPN = cast<PHINode> (PN->use_begin()->getUser());
|
|
assert(EpilogPN->getParent() == Exit && "EpilogPN should be in Exit block");
|
|
|
|
// Add incoming PreHeader from branch around the Loop
|
|
PN->addIncoming(UndefValue::get(PN->getType()), PreHeader);
|
|
|
|
Value *V = PN->getIncomingValueForBlock(Latch);
|
|
Instruction *I = dyn_cast<Instruction>(V);
|
|
if (I && L->contains(I))
|
|
// If value comes from an instruction in the loop add VMap value.
|
|
V = VMap.lookup(I);
|
|
// For the instruction out of the loop, constant or undefined value
|
|
// insert value itself.
|
|
EpilogPN->addIncoming(V, EpilogLatch);
|
|
|
|
assert(EpilogPN->getBasicBlockIndex(EpilogPreHeader) >= 0 &&
|
|
"EpilogPN should have EpilogPreHeader incoming block");
|
|
// Change EpilogPreHeader incoming block to NewExit.
|
|
EpilogPN->setIncomingBlock(EpilogPN->getBasicBlockIndex(EpilogPreHeader),
|
|
NewExit);
|
|
// Now PHIs should look like:
|
|
// NewExit:
|
|
// PN = PHI [I, Latch], [undef, PreHeader]
|
|
// ...
|
|
// Exit:
|
|
// EpilogPN = PHI [PN, NewExit], [VMap[I], EpilogLatch]
|
|
}
|
|
|
|
// Create PHI nodes at NewExit (from the unrolling loop Latch and PreHeader).
|
|
// Update corresponding PHI nodes in epilog loop.
|
|
for (BasicBlock *Succ : successors(Latch)) {
|
|
// Skip this as we already updated phis in exit blocks.
|
|
if (!L->contains(Succ))
|
|
continue;
|
|
for (Instruction &BBI : *Succ) {
|
|
PHINode *PN = dyn_cast<PHINode>(&BBI);
|
|
// Exit when we passed all PHI nodes.
|
|
if (!PN)
|
|
break;
|
|
// Add new PHI nodes to the loop exit block and update epilog
|
|
// PHIs with the new PHI values.
|
|
PHINode *NewPN = PHINode::Create(PN->getType(), 2, PN->getName() + ".unr",
|
|
NewExit->getFirstNonPHI());
|
|
// Adding a value to the new PHI node from the unrolling loop preheader.
|
|
NewPN->addIncoming(PN->getIncomingValueForBlock(NewPreHeader), PreHeader);
|
|
// Adding a value to the new PHI node from the unrolling loop latch.
|
|
NewPN->addIncoming(PN->getIncomingValueForBlock(Latch), Latch);
|
|
|
|
// Update the existing PHI node operand with the value from the new PHI
|
|
// node. Corresponding instruction in epilog loop should be PHI.
|
|
PHINode *VPN = cast<PHINode>(VMap[&BBI]);
|
|
VPN->setIncomingValue(VPN->getBasicBlockIndex(EpilogPreHeader), NewPN);
|
|
}
|
|
}
|
|
|
|
Instruction *InsertPt = NewExit->getTerminator();
|
|
IRBuilder<> B(InsertPt);
|
|
Value *BrLoopExit = B.CreateIsNotNull(ModVal, "lcmp.mod");
|
|
assert(Exit && "Loop must have a single exit block only");
|
|
// Split the exit to maintain loop canonicalization guarantees
|
|
SmallVector<BasicBlock*, 4> Preds(predecessors(Exit));
|
|
SplitBlockPredecessors(Exit, Preds, ".epilog-lcssa", DT, LI,
|
|
PreserveLCSSA);
|
|
// Add the branch to the exit block (around the unrolling loop)
|
|
B.CreateCondBr(BrLoopExit, EpilogPreHeader, Exit);
|
|
InsertPt->eraseFromParent();
|
|
}
|
|
|
|
/// Create a clone of the blocks in a loop and connect them together.
|
|
/// If CreateRemainderLoop is false, loop structure will not be cloned,
|
|
/// otherwise a new loop will be created including all cloned blocks, and the
|
|
/// iterator of it switches to count NewIter down to 0.
|
|
/// The cloned blocks should be inserted between InsertTop and InsertBot.
|
|
/// If loop structure is cloned InsertTop should be new preheader, InsertBot
|
|
/// new loop exit.
|
|
///
|
|
static void CloneLoopBlocks(Loop *L, Value *NewIter,
|
|
const bool CreateRemainderLoop,
|
|
const bool UseEpilogRemainder,
|
|
BasicBlock *InsertTop, BasicBlock *InsertBot,
|
|
BasicBlock *Preheader,
|
|
std::vector<BasicBlock *> &NewBlocks,
|
|
LoopBlocksDFS &LoopBlocks, ValueToValueMapTy &VMap,
|
|
LoopInfo *LI) {
|
|
StringRef suffix = UseEpilogRemainder ? "epil" : "prol";
|
|
BasicBlock *Header = L->getHeader();
|
|
BasicBlock *Latch = L->getLoopLatch();
|
|
Function *F = Header->getParent();
|
|
LoopBlocksDFS::RPOIterator BlockBegin = LoopBlocks.beginRPO();
|
|
LoopBlocksDFS::RPOIterator BlockEnd = LoopBlocks.endRPO();
|
|
Loop *NewLoop = nullptr;
|
|
Loop *ParentLoop = L->getParentLoop();
|
|
if (CreateRemainderLoop) {
|
|
NewLoop = new Loop();
|
|
if (ParentLoop)
|
|
ParentLoop->addChildLoop(NewLoop);
|
|
else
|
|
LI->addTopLevelLoop(NewLoop);
|
|
}
|
|
|
|
// For each block in the original loop, create a new copy,
|
|
// and update the value map with the newly created values.
|
|
for (LoopBlocksDFS::RPOIterator BB = BlockBegin; BB != BlockEnd; ++BB) {
|
|
BasicBlock *NewBB = CloneBasicBlock(*BB, VMap, "." + suffix, F);
|
|
NewBlocks.push_back(NewBB);
|
|
|
|
if (NewLoop)
|
|
NewLoop->addBasicBlockToLoop(NewBB, *LI);
|
|
else if (ParentLoop)
|
|
ParentLoop->addBasicBlockToLoop(NewBB, *LI);
|
|
|
|
VMap[*BB] = NewBB;
|
|
if (Header == *BB) {
|
|
// For the first block, add a CFG connection to this newly
|
|
// created block.
|
|
InsertTop->getTerminator()->setSuccessor(0, NewBB);
|
|
}
|
|
|
|
if (Latch == *BB) {
|
|
// For the last block, if CreateRemainderLoop is false, create a direct
|
|
// jump to InsertBot. If not, create a loop back to cloned head.
|
|
VMap.erase((*BB)->getTerminator());
|
|
BasicBlock *FirstLoopBB = cast<BasicBlock>(VMap[Header]);
|
|
BranchInst *LatchBR = cast<BranchInst>(NewBB->getTerminator());
|
|
IRBuilder<> Builder(LatchBR);
|
|
if (!CreateRemainderLoop) {
|
|
Builder.CreateBr(InsertBot);
|
|
} else {
|
|
PHINode *NewIdx = PHINode::Create(NewIter->getType(), 2,
|
|
suffix + ".iter",
|
|
FirstLoopBB->getFirstNonPHI());
|
|
Value *IdxSub =
|
|
Builder.CreateSub(NewIdx, ConstantInt::get(NewIdx->getType(), 1),
|
|
NewIdx->getName() + ".sub");
|
|
Value *IdxCmp =
|
|
Builder.CreateIsNotNull(IdxSub, NewIdx->getName() + ".cmp");
|
|
Builder.CreateCondBr(IdxCmp, FirstLoopBB, InsertBot);
|
|
NewIdx->addIncoming(NewIter, InsertTop);
|
|
NewIdx->addIncoming(IdxSub, NewBB);
|
|
}
|
|
LatchBR->eraseFromParent();
|
|
}
|
|
}
|
|
|
|
// Change the incoming values to the ones defined in the preheader or
|
|
// cloned loop.
|
|
for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
|
|
PHINode *NewPHI = cast<PHINode>(VMap[&*I]);
|
|
if (!CreateRemainderLoop) {
|
|
if (UseEpilogRemainder) {
|
|
unsigned idx = NewPHI->getBasicBlockIndex(Preheader);
|
|
NewPHI->setIncomingBlock(idx, InsertTop);
|
|
NewPHI->removeIncomingValue(Latch, false);
|
|
} else {
|
|
VMap[&*I] = NewPHI->getIncomingValueForBlock(Preheader);
|
|
cast<BasicBlock>(VMap[Header])->getInstList().erase(NewPHI);
|
|
}
|
|
} else {
|
|
unsigned idx = NewPHI->getBasicBlockIndex(Preheader);
|
|
NewPHI->setIncomingBlock(idx, InsertTop);
|
|
BasicBlock *NewLatch = cast<BasicBlock>(VMap[Latch]);
|
|
idx = NewPHI->getBasicBlockIndex(Latch);
|
|
Value *InVal = NewPHI->getIncomingValue(idx);
|
|
NewPHI->setIncomingBlock(idx, NewLatch);
|
|
if (Value *V = VMap.lookup(InVal))
|
|
NewPHI->setIncomingValue(idx, V);
|
|
}
|
|
}
|
|
if (NewLoop) {
|
|
// Add unroll disable metadata to disable future unrolling for this loop.
|
|
SmallVector<Metadata *, 4> MDs;
|
|
// Reserve first location for self reference to the LoopID metadata node.
|
|
MDs.push_back(nullptr);
|
|
MDNode *LoopID = NewLoop->getLoopID();
|
|
if (LoopID) {
|
|
// First remove any existing loop unrolling metadata.
|
|
for (unsigned i = 1, ie = LoopID->getNumOperands(); i < ie; ++i) {
|
|
bool IsUnrollMetadata = false;
|
|
MDNode *MD = dyn_cast<MDNode>(LoopID->getOperand(i));
|
|
if (MD) {
|
|
const MDString *S = dyn_cast<MDString>(MD->getOperand(0));
|
|
IsUnrollMetadata = S && S->getString().startswith("llvm.loop.unroll.");
|
|
}
|
|
if (!IsUnrollMetadata)
|
|
MDs.push_back(LoopID->getOperand(i));
|
|
}
|
|
}
|
|
|
|
LLVMContext &Context = NewLoop->getHeader()->getContext();
|
|
SmallVector<Metadata *, 1> DisableOperands;
|
|
DisableOperands.push_back(MDString::get(Context, "llvm.loop.unroll.disable"));
|
|
MDNode *DisableNode = MDNode::get(Context, DisableOperands);
|
|
MDs.push_back(DisableNode);
|
|
|
|
MDNode *NewLoopID = MDNode::get(Context, MDs);
|
|
// Set operand 0 to refer to the loop id itself.
|
|
NewLoopID->replaceOperandWith(0, NewLoopID);
|
|
NewLoop->setLoopID(NewLoopID);
|
|
}
|
|
}
|
|
|
|
/// Insert code in the prolog/epilog code when unrolling a loop with a
|
|
/// run-time trip-count.
|
|
///
|
|
/// This method assumes that the loop unroll factor is total number
|
|
/// of loop bodies in the loop after unrolling. (Some folks refer
|
|
/// to the unroll factor as the number of *extra* copies added).
|
|
/// We assume also that the loop unroll factor is a power-of-two. So, after
|
|
/// unrolling the loop, the number of loop bodies executed is 2,
|
|
/// 4, 8, etc. Note - LLVM converts the if-then-sequence to a switch
|
|
/// instruction in SimplifyCFG.cpp. Then, the backend decides how code for
|
|
/// the switch instruction is generated.
|
|
///
|
|
/// ***Prolog case***
|
|
/// extraiters = tripcount % loopfactor
|
|
/// if (extraiters == 0) jump Loop:
|
|
/// else jump Prol:
|
|
/// Prol: LoopBody;
|
|
/// extraiters -= 1 // Omitted if unroll factor is 2.
|
|
/// if (extraiters != 0) jump Prol: // Omitted if unroll factor is 2.
|
|
/// if (tripcount < loopfactor) jump End:
|
|
/// Loop:
|
|
/// ...
|
|
/// End:
|
|
///
|
|
/// ***Epilog case***
|
|
/// extraiters = tripcount % loopfactor
|
|
/// if (tripcount < loopfactor) jump LoopExit:
|
|
/// unroll_iters = tripcount - extraiters
|
|
/// Loop: LoopBody; (executes unroll_iter times);
|
|
/// unroll_iter -= 1
|
|
/// if (unroll_iter != 0) jump Loop:
|
|
/// LoopExit:
|
|
/// if (extraiters == 0) jump EpilExit:
|
|
/// Epil: LoopBody; (executes extraiters times)
|
|
/// extraiters -= 1 // Omitted if unroll factor is 2.
|
|
/// if (extraiters != 0) jump Epil: // Omitted if unroll factor is 2.
|
|
/// EpilExit:
|
|
|
|
bool llvm::UnrollRuntimeLoopRemainder(Loop *L, unsigned Count,
|
|
bool AllowExpensiveTripCount,
|
|
bool UseEpilogRemainder,
|
|
LoopInfo *LI, ScalarEvolution *SE,
|
|
DominatorTree *DT, bool PreserveLCSSA) {
|
|
// for now, only unroll loops that contain a single exit
|
|
if (!L->getExitingBlock())
|
|
return false;
|
|
|
|
// Make sure the loop is in canonical form, and there is a single
|
|
// exit block only.
|
|
if (!L->isLoopSimplifyForm())
|
|
return false;
|
|
BasicBlock *Exit = L->getUniqueExitBlock(); // successor out of loop
|
|
if (!Exit)
|
|
return false;
|
|
|
|
// Use Scalar Evolution to compute the trip count. This allows more loops to
|
|
// be unrolled than relying on induction var simplification.
|
|
if (!SE)
|
|
return false;
|
|
|
|
// Only unroll loops with a computable trip count, and the trip count needs
|
|
// to be an int value (allowing a pointer type is a TODO item).
|
|
const SCEV *BECountSC = SE->getBackedgeTakenCount(L);
|
|
if (isa<SCEVCouldNotCompute>(BECountSC) ||
|
|
!BECountSC->getType()->isIntegerTy())
|
|
return false;
|
|
|
|
unsigned BEWidth = cast<IntegerType>(BECountSC->getType())->getBitWidth();
|
|
|
|
// Add 1 since the backedge count doesn't include the first loop iteration.
|
|
const SCEV *TripCountSC =
|
|
SE->getAddExpr(BECountSC, SE->getConstant(BECountSC->getType(), 1));
|
|
if (isa<SCEVCouldNotCompute>(TripCountSC))
|
|
return false;
|
|
|
|
BasicBlock *Header = L->getHeader();
|
|
BasicBlock *PreHeader = L->getLoopPreheader();
|
|
BranchInst *PreHeaderBR = cast<BranchInst>(PreHeader->getTerminator());
|
|
const DataLayout &DL = Header->getModule()->getDataLayout();
|
|
SCEVExpander Expander(*SE, DL, "loop-unroll");
|
|
if (!AllowExpensiveTripCount &&
|
|
Expander.isHighCostExpansion(TripCountSC, L, PreHeaderBR))
|
|
return false;
|
|
|
|
// This constraint lets us deal with an overflowing trip count easily; see the
|
|
// comment on ModVal below.
|
|
if (Log2_32(Count) > BEWidth)
|
|
return false;
|
|
|
|
// If this loop is nested, then the loop unroller changes the code in the
|
|
// parent loop, so the Scalar Evolution pass needs to be run again.
|
|
if (Loop *ParentLoop = L->getParentLoop())
|
|
SE->forgetLoop(ParentLoop);
|
|
|
|
BasicBlock *Latch = L->getLoopLatch();
|
|
|
|
// Loop structure is the following:
|
|
//
|
|
// PreHeader
|
|
// Header
|
|
// ...
|
|
// Latch
|
|
// Exit
|
|
|
|
BasicBlock *NewPreHeader;
|
|
BasicBlock *NewExit = nullptr;
|
|
BasicBlock *PrologExit = nullptr;
|
|
BasicBlock *EpilogPreHeader = nullptr;
|
|
BasicBlock *PrologPreHeader = nullptr;
|
|
|
|
if (UseEpilogRemainder) {
|
|
// If epilog remainder
|
|
// Split PreHeader to insert a branch around loop for unrolling.
|
|
NewPreHeader = SplitBlock(PreHeader, PreHeader->getTerminator(), DT, LI);
|
|
NewPreHeader->setName(PreHeader->getName() + ".new");
|
|
// Split Exit to create phi nodes from branch above.
|
|
SmallVector<BasicBlock*, 4> Preds(predecessors(Exit));
|
|
NewExit = SplitBlockPredecessors(Exit, Preds, ".unr-lcssa",
|
|
DT, LI, PreserveLCSSA);
|
|
// Split NewExit to insert epilog remainder loop.
|
|
EpilogPreHeader = SplitBlock(NewExit, NewExit->getTerminator(), DT, LI);
|
|
EpilogPreHeader->setName(Header->getName() + ".epil.preheader");
|
|
} else {
|
|
// If prolog remainder
|
|
// Split the original preheader twice to insert prolog remainder loop
|
|
PrologPreHeader = SplitEdge(PreHeader, Header, DT, LI);
|
|
PrologPreHeader->setName(Header->getName() + ".prol.preheader");
|
|
PrologExit = SplitBlock(PrologPreHeader, PrologPreHeader->getTerminator(),
|
|
DT, LI);
|
|
PrologExit->setName(Header->getName() + ".prol.loopexit");
|
|
// Split PrologExit to get NewPreHeader.
|
|
NewPreHeader = SplitBlock(PrologExit, PrologExit->getTerminator(), DT, LI);
|
|
NewPreHeader->setName(PreHeader->getName() + ".new");
|
|
}
|
|
// Loop structure should be the following:
|
|
// Epilog Prolog
|
|
//
|
|
// PreHeader PreHeader
|
|
// *NewPreHeader *PrologPreHeader
|
|
// Header *PrologExit
|
|
// ... *NewPreHeader
|
|
// Latch Header
|
|
// *NewExit ...
|
|
// *EpilogPreHeader Latch
|
|
// Exit Exit
|
|
|
|
// Calculate conditions for branch around loop for unrolling
|
|
// in epilog case and around prolog remainder loop in prolog case.
|
|
// Compute the number of extra iterations required, which is:
|
|
// extra iterations = run-time trip count % loop unroll factor
|
|
PreHeaderBR = cast<BranchInst>(PreHeader->getTerminator());
|
|
Value *TripCount = Expander.expandCodeFor(TripCountSC, TripCountSC->getType(),
|
|
PreHeaderBR);
|
|
Value *BECount = Expander.expandCodeFor(BECountSC, BECountSC->getType(),
|
|
PreHeaderBR);
|
|
IRBuilder<> B(PreHeaderBR);
|
|
Value *ModVal;
|
|
// Calculate ModVal = (BECount + 1) % Count.
|
|
// Note that TripCount is BECount + 1.
|
|
if (isPowerOf2_32(Count)) {
|
|
// When Count is power of 2 we don't BECount for epilog case, however we'll
|
|
// need it for a branch around unrolling loop for prolog case.
|
|
ModVal = B.CreateAnd(TripCount, Count - 1, "xtraiter");
|
|
// 1. There are no iterations to be run in the prolog/epilog loop.
|
|
// OR
|
|
// 2. The addition computing TripCount overflowed.
|
|
//
|
|
// If (2) is true, we know that TripCount really is (1 << BEWidth) and so
|
|
// the number of iterations that remain to be run in the original loop is a
|
|
// multiple Count == (1 << Log2(Count)) because Log2(Count) <= BEWidth (we
|
|
// explicitly check this above).
|
|
} else {
|
|
// As (BECount + 1) can potentially unsigned overflow we count
|
|
// (BECount % Count) + 1 which is overflow safe as BECount % Count < Count.
|
|
Value *ModValTmp = B.CreateURem(BECount,
|
|
ConstantInt::get(BECount->getType(),
|
|
Count));
|
|
Value *ModValAdd = B.CreateAdd(ModValTmp,
|
|
ConstantInt::get(ModValTmp->getType(), 1));
|
|
// At that point (BECount % Count) + 1 could be equal to Count.
|
|
// To handle this case we need to take mod by Count one more time.
|
|
ModVal = B.CreateURem(ModValAdd,
|
|
ConstantInt::get(BECount->getType(), Count),
|
|
"xtraiter");
|
|
}
|
|
Value *BranchVal =
|
|
UseEpilogRemainder ? B.CreateICmpULT(BECount,
|
|
ConstantInt::get(BECount->getType(),
|
|
Count - 1)) :
|
|
B.CreateIsNotNull(ModVal, "lcmp.mod");
|
|
BasicBlock *RemainderLoop = UseEpilogRemainder ? NewExit : PrologPreHeader;
|
|
BasicBlock *UnrollingLoop = UseEpilogRemainder ? NewPreHeader : PrologExit;
|
|
// Branch to either remainder (extra iterations) loop or unrolling loop.
|
|
B.CreateCondBr(BranchVal, RemainderLoop, UnrollingLoop);
|
|
PreHeaderBR->eraseFromParent();
|
|
Function *F = Header->getParent();
|
|
// Get an ordered list of blocks in the loop to help with the ordering of the
|
|
// cloned blocks in the prolog/epilog code
|
|
LoopBlocksDFS LoopBlocks(L);
|
|
LoopBlocks.perform(LI);
|
|
|
|
//
|
|
// For each extra loop iteration, create a copy of the loop's basic blocks
|
|
// and generate a condition that branches to the copy depending on the
|
|
// number of 'left over' iterations.
|
|
//
|
|
std::vector<BasicBlock *> NewBlocks;
|
|
ValueToValueMapTy VMap;
|
|
|
|
// For unroll factor 2 remainder loop will have 1 iterations.
|
|
// Do not create 1 iteration loop.
|
|
bool CreateRemainderLoop = (Count != 2);
|
|
|
|
// Clone all the basic blocks in the loop. If Count is 2, we don't clone
|
|
// the loop, otherwise we create a cloned loop to execute the extra
|
|
// iterations. This function adds the appropriate CFG connections.
|
|
BasicBlock *InsertBot = UseEpilogRemainder ? Exit : PrologExit;
|
|
BasicBlock *InsertTop = UseEpilogRemainder ? EpilogPreHeader : PrologPreHeader;
|
|
CloneLoopBlocks(L, ModVal, CreateRemainderLoop, UseEpilogRemainder, InsertTop,
|
|
InsertBot, NewPreHeader, NewBlocks, LoopBlocks, VMap, LI);
|
|
|
|
// Insert the cloned blocks into the function.
|
|
F->getBasicBlockList().splice(InsertBot->getIterator(),
|
|
F->getBasicBlockList(),
|
|
NewBlocks[0]->getIterator(),
|
|
F->end());
|
|
|
|
// Loop structure should be the following:
|
|
// Epilog Prolog
|
|
//
|
|
// PreHeader PreHeader
|
|
// NewPreHeader PrologPreHeader
|
|
// Header PrologHeader
|
|
// ... ...
|
|
// Latch PrologLatch
|
|
// NewExit PrologExit
|
|
// EpilogPreHeader NewPreHeader
|
|
// EpilogHeader Header
|
|
// ... ...
|
|
// EpilogLatch Latch
|
|
// Exit Exit
|
|
|
|
// Rewrite the cloned instruction operands to use the values created when the
|
|
// clone is created.
|
|
for (BasicBlock *BB : NewBlocks) {
|
|
for (Instruction &I : *BB) {
|
|
RemapInstruction(&I, VMap,
|
|
RF_NoModuleLevelChanges | RF_IgnoreMissingLocals);
|
|
}
|
|
}
|
|
|
|
if (UseEpilogRemainder) {
|
|
// Connect the epilog code to the original loop and update the
|
|
// PHI functions.
|
|
ConnectEpilog(L, ModVal, NewExit, Exit, PreHeader,
|
|
EpilogPreHeader, NewPreHeader, VMap, DT, LI,
|
|
PreserveLCSSA);
|
|
|
|
// Update counter in loop for unrolling.
|
|
// I should be multiply of Count.
|
|
IRBuilder<> B2(NewPreHeader->getTerminator());
|
|
Value *TestVal = B2.CreateSub(TripCount, ModVal, "unroll_iter");
|
|
BranchInst *LatchBR = cast<BranchInst>(Latch->getTerminator());
|
|
B2.SetInsertPoint(LatchBR);
|
|
PHINode *NewIdx = PHINode::Create(TestVal->getType(), 2, "niter",
|
|
Header->getFirstNonPHI());
|
|
Value *IdxSub =
|
|
B2.CreateSub(NewIdx, ConstantInt::get(NewIdx->getType(), 1),
|
|
NewIdx->getName() + ".nsub");
|
|
Value *IdxCmp;
|
|
if (LatchBR->getSuccessor(0) == Header)
|
|
IdxCmp = B2.CreateIsNotNull(IdxSub, NewIdx->getName() + ".ncmp");
|
|
else
|
|
IdxCmp = B2.CreateIsNull(IdxSub, NewIdx->getName() + ".ncmp");
|
|
NewIdx->addIncoming(TestVal, NewPreHeader);
|
|
NewIdx->addIncoming(IdxSub, Latch);
|
|
LatchBR->setCondition(IdxCmp);
|
|
} else {
|
|
// Connect the prolog code to the original loop and update the
|
|
// PHI functions.
|
|
ConnectProlog(L, BECount, Count, PrologExit, PreHeader, NewPreHeader,
|
|
VMap, DT, LI, PreserveLCSSA);
|
|
}
|
|
NumRuntimeUnrolled++;
|
|
return true;
|
|
}
|