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llvm-project/llvm/lib/CodeGen/ShrinkWrapping.cpp

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//===-- ShrinkWrapping.cpp - Reduce spills/restores of callee-saved regs --===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements a shrink wrapping variant of prolog/epilog insertion:
// - Spills and restores of callee-saved registers (CSRs) are placed in the
// machine CFG to tightly surround their uses so that execution paths that
// do not use CSRs do not pay the spill/restore penalty.
//
// - Avoiding placment of spills/restores in loops: if a CSR is used inside a
// loop the spills are placed in the loop preheader, and restores are
// placed in the loop exit nodes (the successors of loop _exiting_ nodes).
//
// - Covering paths without CSR uses:
// If a region in a CFG uses CSRs and has multiple entry and/or exit points,
// the use info for the CSRs inside the region is propagated outward in the
// CFG to ensure validity of the spill/restore placements. This decreases
// the effectiveness of shrink wrapping but does not require edge splitting
// in the machine CFG.
//
// This shrink wrapping implementation uses an iterative analysis to determine
// which basic blocks require spills and restores for CSRs.
//
// This pass uses MachineDominators and MachineLoopInfo. Loop information
// is used to prevent placement of callee-saved register spills/restores
// in the bodies of loops.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "shrink-wrap"
#include "PrologEpilogInserter.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/ADT/SparseBitVector.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/PostOrderIterator.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/Statistic.h"
#include <sstream>
using namespace llvm;
STATISTIC(numSRReduced, "Number of CSR spills+restores reduced.");
// Shrink Wrapping:
static cl::opt<bool>
ShrinkWrapping("shrink-wrap",
cl::desc("Shrink wrap callee-saved register spills/restores"));
// Shrink wrap only the specified function, a debugging aid.
static cl::opt<std::string>
ShrinkWrapFunc("shrink-wrap-func", cl::Hidden,
cl::desc("Shrink wrap the specified function"),
cl::value_desc("funcname"),
cl::init(""));
// Debugging level for shrink wrapping.
enum ShrinkWrapDebugLevel {
None, BasicInfo, Iterations, Details
};
static cl::opt<enum ShrinkWrapDebugLevel>
ShrinkWrapDebugging("shrink-wrap-dbg", cl::Hidden,
cl::desc("Print shrink wrapping debugging information"),
cl::values(
clEnumVal(None , "disable debug output"),
clEnumVal(BasicInfo , "print basic DF sets"),
clEnumVal(Iterations, "print SR sets for each iteration"),
clEnumVal(Details , "print all DF sets"),
clEnumValEnd));
void PEI::getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
if (ShrinkWrapping || ShrinkWrapFunc != "") {
AU.addRequired<MachineLoopInfo>();
AU.addRequired<MachineDominatorTree>();
}
AU.addPreserved<MachineLoopInfo>();
AU.addPreserved<MachineDominatorTree>();
AU.addRequired<TargetPassConfig>();
MachineFunctionPass::getAnalysisUsage(AU);
}
//===----------------------------------------------------------------------===//
// ShrinkWrapping implementation
//===----------------------------------------------------------------------===//
// Convienences for dealing with machine loops.
MachineBasicBlock* PEI::getTopLevelLoopPreheader(MachineLoop* LP) {
assert(LP && "Machine loop is NULL.");
MachineBasicBlock* PHDR = LP->getLoopPreheader();
MachineLoop* PLP = LP->getParentLoop();
while (PLP) {
PHDR = PLP->getLoopPreheader();
PLP = PLP->getParentLoop();
}
return PHDR;
}
MachineLoop* PEI::getTopLevelLoopParent(MachineLoop *LP) {
if (LP == 0)
return 0;
MachineLoop* PLP = LP->getParentLoop();
while (PLP) {
LP = PLP;
PLP = PLP->getParentLoop();
}
return LP;
}
bool PEI::isReturnBlock(MachineBasicBlock* MBB) {
return (MBB && !MBB->empty() && MBB->back().isReturn());
}
// Initialize shrink wrapping DFA sets, called before iterations.
void PEI::clearAnticAvailSets() {
AnticIn.clear();
AnticOut.clear();
AvailIn.clear();
AvailOut.clear();
}
// Clear all sets constructed by shrink wrapping.
void PEI::clearAllSets() {
ReturnBlocks.clear();
clearAnticAvailSets();
UsedCSRegs.clear();
CSRUsed.clear();
TLLoops.clear();
CSRSave.clear();
CSRRestore.clear();
}
// Initialize all shrink wrapping data.
void PEI::initShrinkWrappingInfo() {
clearAllSets();
EntryBlock = 0;
#ifndef NDEBUG
HasFastExitPath = false;
#endif
ShrinkWrapThisFunction = ShrinkWrapping;
// DEBUG: enable or disable shrink wrapping for the current function
// via --shrink-wrap-func=<funcname>.
#ifndef NDEBUG
if (ShrinkWrapFunc != "") {
std::string MFName = MF->getName().str();
ShrinkWrapThisFunction = (MFName == ShrinkWrapFunc);
}
#endif
}
/// placeCSRSpillsAndRestores - determine which MBBs of the function
/// need save, restore code for callee-saved registers by doing a DF analysis
/// similar to the one used in code motion (GVNPRE). This produces maps of MBBs
/// to sets of registers (CSRs) for saves and restores. MachineLoopInfo
/// is used to ensure that CSR save/restore code is not placed inside loops.
/// This function computes the maps of MBBs -> CSRs to spill and restore
/// in CSRSave, CSRRestore.
///
/// If shrink wrapping is not being performed, place all spills in
/// the entry block, all restores in return blocks. In this case,
/// CSRSave has a single mapping, CSRRestore has mappings for each
/// return block.
///
void PEI::placeCSRSpillsAndRestores(MachineFunction &Fn) {
DEBUG(MF = &Fn);
initShrinkWrappingInfo();
DEBUG(if (ShrinkWrapThisFunction) {
dbgs() << "Place CSR spills/restores for "
<< MF->getName() << "\n";
});
if (calculateSets(Fn))
placeSpillsAndRestores(Fn);
}
/// calcAnticInOut - calculate the anticipated in/out reg sets
/// for the given MBB by looking forward in the MCFG at MBB's
/// successors.
///
bool PEI::calcAnticInOut(MachineBasicBlock* MBB) {
bool changed = false;
// AnticOut[MBB] = INTERSECT(AnticIn[S] for S in SUCCESSORS(MBB))
SmallVector<MachineBasicBlock*, 4> successors;
for (MachineBasicBlock::succ_iterator SI = MBB->succ_begin(),
SE = MBB->succ_end(); SI != SE; ++SI) {
MachineBasicBlock* SUCC = *SI;
if (SUCC != MBB)
successors.push_back(SUCC);
}
unsigned i = 0, e = successors.size();
if (i != e) {
CSRegSet prevAnticOut = AnticOut[MBB];
MachineBasicBlock* SUCC = successors[i];
AnticOut[MBB] = AnticIn[SUCC];
for (++i; i != e; ++i) {
SUCC = successors[i];
AnticOut[MBB] &= AnticIn[SUCC];
}
if (prevAnticOut != AnticOut[MBB])
changed = true;
}
// AnticIn[MBB] = UNION(CSRUsed[MBB], AnticOut[MBB]);
CSRegSet prevAnticIn = AnticIn[MBB];
AnticIn[MBB] = CSRUsed[MBB] | AnticOut[MBB];
if (prevAnticIn != AnticIn[MBB])
changed = true;
return changed;
}
/// calcAvailInOut - calculate the available in/out reg sets
/// for the given MBB by looking backward in the MCFG at MBB's
/// predecessors.
///
bool PEI::calcAvailInOut(MachineBasicBlock* MBB) {
bool changed = false;
// AvailIn[MBB] = INTERSECT(AvailOut[P] for P in PREDECESSORS(MBB))
SmallVector<MachineBasicBlock*, 4> predecessors;
for (MachineBasicBlock::pred_iterator PI = MBB->pred_begin(),
PE = MBB->pred_end(); PI != PE; ++PI) {
MachineBasicBlock* PRED = *PI;
if (PRED != MBB)
predecessors.push_back(PRED);
}
unsigned i = 0, e = predecessors.size();
if (i != e) {
CSRegSet prevAvailIn = AvailIn[MBB];
MachineBasicBlock* PRED = predecessors[i];
AvailIn[MBB] = AvailOut[PRED];
for (++i; i != e; ++i) {
PRED = predecessors[i];
AvailIn[MBB] &= AvailOut[PRED];
}
if (prevAvailIn != AvailIn[MBB])
changed = true;
}
// AvailOut[MBB] = UNION(CSRUsed[MBB], AvailIn[MBB]);
CSRegSet prevAvailOut = AvailOut[MBB];
AvailOut[MBB] = CSRUsed[MBB] | AvailIn[MBB];
if (prevAvailOut != AvailOut[MBB])
changed = true;
return changed;
}
/// calculateAnticAvail - build the sets anticipated and available
/// registers in the MCFG of the current function iteratively,
/// doing a combined forward and backward analysis.
///
void PEI::calculateAnticAvail(MachineFunction &Fn) {
// Initialize data flow sets.
clearAnticAvailSets();
// Calculate Antic{In,Out} and Avail{In,Out} iteratively on the MCFG.
bool changed = true;
unsigned iterations = 0;
while (changed) {
changed = false;
++iterations;
for (MachineFunction::iterator MBBI = Fn.begin(), MBBE = Fn.end();
MBBI != MBBE; ++MBBI) {
MachineBasicBlock* MBB = MBBI;
// Calculate anticipated in, out regs at MBB from
// anticipated at successors of MBB.
changed |= calcAnticInOut(MBB);
// Calculate available in, out regs at MBB from
// available at predecessors of MBB.
changed |= calcAvailInOut(MBB);
}
}
DEBUG({
if (ShrinkWrapDebugging >= Details) {
dbgs()
<< "-----------------------------------------------------------\n"
<< " Antic/Avail Sets:\n"
<< "-----------------------------------------------------------\n"
<< "iterations = " << iterations << "\n"
<< "-----------------------------------------------------------\n"
<< "MBB | USED | ANTIC_IN | ANTIC_OUT | AVAIL_IN | AVAIL_OUT\n"
<< "-----------------------------------------------------------\n";
for (MachineFunction::iterator MBBI = Fn.begin(), MBBE = Fn.end();
MBBI != MBBE; ++MBBI) {
MachineBasicBlock* MBB = MBBI;
dumpSets(MBB);
}
dbgs()
<< "-----------------------------------------------------------\n";
}
});
}
/// propagateUsesAroundLoop - copy used register info from MBB to all blocks
/// of the loop given by LP and its parent loops. This prevents spills/restores
/// from being placed in the bodies of loops.
///
void PEI::propagateUsesAroundLoop(MachineBasicBlock* MBB, MachineLoop* LP) {
if (! MBB || !LP)
return;
std::vector<MachineBasicBlock*> loopBlocks = LP->getBlocks();
for (unsigned i = 0, e = loopBlocks.size(); i != e; ++i) {
MachineBasicBlock* LBB = loopBlocks[i];
if (LBB == MBB)
continue;
if (CSRUsed[LBB].contains(CSRUsed[MBB]))
continue;
CSRUsed[LBB] |= CSRUsed[MBB];
}
}
/// calculateSets - collect the CSRs used in this function, compute
/// the DF sets that describe the initial minimal regions in the
/// Machine CFG around which CSR spills and restores must be placed.
///
/// Additionally, this function decides if shrink wrapping should
/// be disabled for the current function, checking the following:
/// 1. the current function has more than 500 MBBs: heuristic limit
/// on function size to reduce compile time impact of the current
/// iterative algorithm.
/// 2. all CSRs are used in the entry block.
/// 3. all CSRs are used in all immediate successors of the entry block.
/// 4. all CSRs are used in a subset of blocks, each of which dominates
/// all return blocks. These blocks, taken as a subgraph of the MCFG,
/// are equivalent to the entry block since all execution paths pass
/// through them.
///
bool PEI::calculateSets(MachineFunction &Fn) {
// Sets used to compute spill, restore placement sets.
const std::vector<CalleeSavedInfo> CSI =
Fn.getFrameInfo()->getCalleeSavedInfo();
// If no CSRs used, we are done.
if (CSI.empty()) {
DEBUG(if (ShrinkWrapThisFunction)
dbgs() << "DISABLED: " << Fn.getName()
<< ": uses no callee-saved registers\n");
return false;
}
// Save refs to entry and return blocks.
EntryBlock = Fn.begin();
for (MachineFunction::iterator MBB = Fn.begin(), E = Fn.end();
MBB != E; ++MBB)
if (isReturnBlock(MBB))
ReturnBlocks.push_back(MBB);
// Determine if this function has fast exit paths.
DEBUG(if (ShrinkWrapThisFunction)
findFastExitPath());
// Limit shrink wrapping via the current iterative bit vector
// implementation to functions with <= 500 MBBs.
if (Fn.size() > 500) {
DEBUG(if (ShrinkWrapThisFunction)
dbgs() << "DISABLED: " << Fn.getName()
<< ": too large (" << Fn.size() << " MBBs)\n");
ShrinkWrapThisFunction = false;
}
// Return now if not shrink wrapping.
if (! ShrinkWrapThisFunction)
return false;
// Collect set of used CSRs.
for (unsigned inx = 0, e = CSI.size(); inx != e; ++inx) {
UsedCSRegs.set(inx);
}
// Walk instructions in all MBBs, create CSRUsed[] sets, choose
// whether or not to shrink wrap this function.
MachineLoopInfo &LI = getAnalysis<MachineLoopInfo>();
MachineDominatorTree &DT = getAnalysis<MachineDominatorTree>();
const TargetRegisterInfo *TRI = Fn.getTarget().getRegisterInfo();
bool allCSRUsesInEntryBlock = true;
for (MachineFunction::iterator MBBI = Fn.begin(), MBBE = Fn.end();
MBBI != MBBE; ++MBBI) {
MachineBasicBlock* MBB = MBBI;
for (MachineBasicBlock::iterator I = MBB->begin(); I != MBB->end(); ++I) {
for (unsigned inx = 0, e = CSI.size(); inx != e; ++inx) {
unsigned Reg = CSI[inx].getReg();
// If instruction I reads or modifies Reg, add it to UsedCSRegs,
// CSRUsed map for the current block.
for (unsigned opInx = 0, opEnd = I->getNumOperands();
opInx != opEnd; ++opInx) {
const MachineOperand &MO = I->getOperand(opInx);
if (! (MO.isReg() && (MO.isUse() || MO.isDef())))
continue;
unsigned MOReg = MO.getReg();
if (!MOReg)
continue;
if (MOReg == Reg ||
(TargetRegisterInfo::isPhysicalRegister(MOReg) &&
TargetRegisterInfo::isPhysicalRegister(Reg) &&
TRI->isSubRegister(Reg, MOReg))) {
// CSR Reg is defined/used in block MBB.
CSRUsed[MBB].set(inx);
// Check for uses in EntryBlock.
if (MBB != EntryBlock)
allCSRUsesInEntryBlock = false;
}
}
}
}
if (CSRUsed[MBB].empty())
continue;
// Propagate CSRUsed[MBB] in loops
if (MachineLoop* LP = LI.getLoopFor(MBB)) {
// Add top level loop to work list.
MachineBasicBlock* HDR = getTopLevelLoopPreheader(LP);
MachineLoop* PLP = getTopLevelLoopParent(LP);
if (! HDR) {
HDR = PLP->getHeader();
assert(HDR->pred_size() > 0 && "Loop header has no predecessors?");
MachineBasicBlock::pred_iterator PI = HDR->pred_begin();
HDR = *PI;
}
TLLoops[HDR] = PLP;
// Push uses from inside loop to its parent loops,
// or to all other MBBs in its loop.
if (LP->getLoopDepth() > 1) {
for (MachineLoop* PLP = LP->getParentLoop(); PLP;
PLP = PLP->getParentLoop()) {
propagateUsesAroundLoop(MBB, PLP);
}
} else {
propagateUsesAroundLoop(MBB, LP);
}
}
}
if (allCSRUsesInEntryBlock) {
DEBUG(dbgs() << "DISABLED: " << Fn.getName()
<< ": all CSRs used in EntryBlock\n");
ShrinkWrapThisFunction = false;
} else {
bool allCSRsUsedInEntryFanout = true;
for (MachineBasicBlock::succ_iterator SI = EntryBlock->succ_begin(),
SE = EntryBlock->succ_end(); SI != SE; ++SI) {
MachineBasicBlock* SUCC = *SI;
if (CSRUsed[SUCC] != UsedCSRegs)
allCSRsUsedInEntryFanout = false;
}
if (allCSRsUsedInEntryFanout) {
DEBUG(dbgs() << "DISABLED: " << Fn.getName()
<< ": all CSRs used in imm successors of EntryBlock\n");
ShrinkWrapThisFunction = false;
}
}
if (ShrinkWrapThisFunction) {
// Check if MBB uses CSRs and dominates all exit nodes.
// Such nodes are equiv. to the entry node w.r.t.
// CSR uses: every path through the function must
// pass through this node. If each CSR is used at least
// once by these nodes, shrink wrapping is disabled.
CSRegSet CSRUsedInChokePoints;
for (MachineFunction::iterator MBBI = Fn.begin(), MBBE = Fn.end();
MBBI != MBBE; ++MBBI) {
MachineBasicBlock* MBB = MBBI;
if (MBB == EntryBlock || CSRUsed[MBB].empty() || MBB->succ_size() < 1)
continue;
bool dominatesExitNodes = true;
for (unsigned ri = 0, re = ReturnBlocks.size(); ri != re; ++ri)
if (! DT.dominates(MBB, ReturnBlocks[ri])) {
dominatesExitNodes = false;
break;
}
if (dominatesExitNodes) {
CSRUsedInChokePoints |= CSRUsed[MBB];
if (CSRUsedInChokePoints == UsedCSRegs) {
DEBUG(dbgs() << "DISABLED: " << Fn.getName()
<< ": all CSRs used in choke point(s) at "
<< getBasicBlockName(MBB) << "\n");
ShrinkWrapThisFunction = false;
break;
}
}
}
}
// Return now if we have decided not to apply shrink wrapping
// to the current function.
if (! ShrinkWrapThisFunction)
return false;
DEBUG({
dbgs() << "ENABLED: " << Fn.getName();
if (HasFastExitPath)
dbgs() << " (fast exit path)";
dbgs() << "\n";
if (ShrinkWrapDebugging >= BasicInfo) {
dbgs() << "------------------------------"
<< "-----------------------------\n";
dbgs() << "UsedCSRegs = " << stringifyCSRegSet(UsedCSRegs) << "\n";
if (ShrinkWrapDebugging >= Details) {
dbgs() << "------------------------------"
<< "-----------------------------\n";
dumpAllUsed();
}
}
});
// Build initial DF sets to determine minimal regions in the
// Machine CFG around which CSRs must be spilled and restored.
calculateAnticAvail(Fn);
return true;
}
/// addUsesForMEMERegion - add uses of CSRs spilled or restored in
/// multi-entry, multi-exit (MEME) regions so spill and restore
/// placement will not break code that enters or leaves a
/// shrink-wrapped region by inducing spills with no matching
/// restores or restores with no matching spills. A MEME region
/// is a subgraph of the MCFG with multiple entry edges, multiple
/// exit edges, or both. This code propagates use information
/// through the MCFG until all paths requiring spills and restores
/// _outside_ the computed minimal placement regions have been covered.
///
bool PEI::addUsesForMEMERegion(MachineBasicBlock* MBB,
SmallVector<MachineBasicBlock*, 4>& blks) {
if (MBB->succ_size() < 2 && MBB->pred_size() < 2) {
bool processThisBlock = false;
for (MachineBasicBlock::succ_iterator SI = MBB->succ_begin(),
SE = MBB->succ_end(); SI != SE; ++SI) {
MachineBasicBlock* SUCC = *SI;
if (SUCC->pred_size() > 1) {
processThisBlock = true;
break;
}
}
if (!CSRRestore[MBB].empty() && MBB->succ_size() > 0) {
for (MachineBasicBlock::pred_iterator PI = MBB->pred_begin(),
PE = MBB->pred_end(); PI != PE; ++PI) {
MachineBasicBlock* PRED = *PI;
if (PRED->succ_size() > 1) {
processThisBlock = true;
break;
}
}
}
if (! processThisBlock)
return false;
}
CSRegSet prop;
if (!CSRSave[MBB].empty())
prop = CSRSave[MBB];
else if (!CSRRestore[MBB].empty())
prop = CSRRestore[MBB];
else
prop = CSRUsed[MBB];
if (prop.empty())
return false;
// Propagate selected bits to successors, predecessors of MBB.
bool addedUses = false;
for (MachineBasicBlock::succ_iterator SI = MBB->succ_begin(),
SE = MBB->succ_end(); SI != SE; ++SI) {
MachineBasicBlock* SUCC = *SI;
// Self-loop
if (SUCC == MBB)
continue;
if (! CSRUsed[SUCC].contains(prop)) {
CSRUsed[SUCC] |= prop;
addedUses = true;
blks.push_back(SUCC);
DEBUG(if (ShrinkWrapDebugging >= Iterations)
dbgs() << getBasicBlockName(MBB)
<< "(" << stringifyCSRegSet(prop) << ")->"
<< "successor " << getBasicBlockName(SUCC) << "\n");
}
}
for (MachineBasicBlock::pred_iterator PI = MBB->pred_begin(),
PE = MBB->pred_end(); PI != PE; ++PI) {
MachineBasicBlock* PRED = *PI;
// Self-loop
if (PRED == MBB)
continue;
if (! CSRUsed[PRED].contains(prop)) {
CSRUsed[PRED] |= prop;
addedUses = true;
blks.push_back(PRED);
DEBUG(if (ShrinkWrapDebugging >= Iterations)
dbgs() << getBasicBlockName(MBB)
<< "(" << stringifyCSRegSet(prop) << ")->"
<< "predecessor " << getBasicBlockName(PRED) << "\n");
}
}
return addedUses;
}
/// addUsesForTopLevelLoops - add uses for CSRs used inside top
/// level loops to the exit blocks of those loops.
///
bool PEI::addUsesForTopLevelLoops(SmallVector<MachineBasicBlock*, 4>& blks) {
bool addedUses = false;
// Place restores for top level loops where needed.
for (DenseMap<MachineBasicBlock*, MachineLoop*>::iterator
I = TLLoops.begin(), E = TLLoops.end(); I != E; ++I) {
MachineBasicBlock* MBB = I->first;
MachineLoop* LP = I->second;
MachineBasicBlock* HDR = LP->getHeader();
SmallVector<MachineBasicBlock*, 4> exitBlocks;
CSRegSet loopSpills;
loopSpills = CSRSave[MBB];
if (CSRSave[MBB].empty()) {
loopSpills = CSRUsed[HDR];
assert(!loopSpills.empty() && "No CSRs used in loop?");
} else if (CSRRestore[MBB].contains(CSRSave[MBB]))
continue;
LP->getExitBlocks(exitBlocks);
assert(exitBlocks.size() > 0 && "Loop has no top level exit blocks?");
for (unsigned i = 0, e = exitBlocks.size(); i != e; ++i) {
MachineBasicBlock* EXB = exitBlocks[i];
if (! CSRUsed[EXB].contains(loopSpills)) {
CSRUsed[EXB] |= loopSpills;
addedUses = true;
DEBUG(if (ShrinkWrapDebugging >= Iterations)
dbgs() << "LOOP " << getBasicBlockName(MBB)
<< "(" << stringifyCSRegSet(loopSpills) << ")->"
<< getBasicBlockName(EXB) << "\n");
if (EXB->succ_size() > 1 || EXB->pred_size() > 1)
blks.push_back(EXB);
}
}
}
return addedUses;
}
/// calcSpillPlacements - determine which CSRs should be spilled
/// in MBB using AnticIn sets of MBB's predecessors, keeping track
/// of changes to spilled reg sets. Add MBB to the set of blocks
/// that need to be processed for propagating use info to cover
/// multi-entry/exit regions.
///
bool PEI::calcSpillPlacements(MachineBasicBlock* MBB,
SmallVector<MachineBasicBlock*, 4> &blks,
CSRegBlockMap &prevSpills) {
bool placedSpills = false;
// Intersect (CSRegs - AnticIn[P]) for P in Predecessors(MBB)
CSRegSet anticInPreds;
SmallVector<MachineBasicBlock*, 4> predecessors;
for (MachineBasicBlock::pred_iterator PI = MBB->pred_begin(),
PE = MBB->pred_end(); PI != PE; ++PI) {
MachineBasicBlock* PRED = *PI;
if (PRED != MBB)
predecessors.push_back(PRED);
}
unsigned i = 0, e = predecessors.size();
if (i != e) {
MachineBasicBlock* PRED = predecessors[i];
anticInPreds = UsedCSRegs - AnticIn[PRED];
for (++i; i != e; ++i) {
PRED = predecessors[i];
anticInPreds &= (UsedCSRegs - AnticIn[PRED]);
}
} else {
// Handle uses in entry blocks (which have no predecessors).
// This is necessary because the DFA formulation assumes the
// entry and (multiple) exit nodes cannot have CSR uses, which
// is not the case in the real world.
anticInPreds = UsedCSRegs;
}
// Compute spills required at MBB:
CSRSave[MBB] |= (AnticIn[MBB] - AvailIn[MBB]) & anticInPreds;
if (! CSRSave[MBB].empty()) {
if (MBB == EntryBlock) {
for (unsigned ri = 0, re = ReturnBlocks.size(); ri != re; ++ri)
CSRRestore[ReturnBlocks[ri]] |= CSRSave[MBB];
} else {
// Reset all regs spilled in MBB that are also spilled in EntryBlock.
if (CSRSave[EntryBlock].intersects(CSRSave[MBB])) {
CSRSave[MBB] = CSRSave[MBB] - CSRSave[EntryBlock];
}
}
}
placedSpills = (CSRSave[MBB] != prevSpills[MBB]);
prevSpills[MBB] = CSRSave[MBB];
// Remember this block for adding restores to successor
// blocks for multi-entry region.
if (placedSpills)
blks.push_back(MBB);
DEBUG(if (! CSRSave[MBB].empty() && ShrinkWrapDebugging >= Iterations)
dbgs() << "SAVE[" << getBasicBlockName(MBB) << "] = "
<< stringifyCSRegSet(CSRSave[MBB]) << "\n");
return placedSpills;
}
/// calcRestorePlacements - determine which CSRs should be restored
/// in MBB using AvailOut sets of MBB's succcessors, keeping track
/// of changes to restored reg sets. Add MBB to the set of blocks
/// that need to be processed for propagating use info to cover
/// multi-entry/exit regions.
///
bool PEI::calcRestorePlacements(MachineBasicBlock* MBB,
SmallVector<MachineBasicBlock*, 4> &blks,
CSRegBlockMap &prevRestores) {
bool placedRestores = false;
// Intersect (CSRegs - AvailOut[S]) for S in Successors(MBB)
CSRegSet availOutSucc;
SmallVector<MachineBasicBlock*, 4> successors;
for (MachineBasicBlock::succ_iterator SI = MBB->succ_begin(),
SE = MBB->succ_end(); SI != SE; ++SI) {
MachineBasicBlock* SUCC = *SI;
if (SUCC != MBB)
successors.push_back(SUCC);
}
unsigned i = 0, e = successors.size();
if (i != e) {
MachineBasicBlock* SUCC = successors[i];
availOutSucc = UsedCSRegs - AvailOut[SUCC];
for (++i; i != e; ++i) {
SUCC = successors[i];
availOutSucc &= (UsedCSRegs - AvailOut[SUCC]);
}
} else {
if (! CSRUsed[MBB].empty() || ! AvailOut[MBB].empty()) {
// Handle uses in return blocks (which have no successors).
// This is necessary because the DFA formulation assumes the
// entry and (multiple) exit nodes cannot have CSR uses, which
// is not the case in the real world.
availOutSucc = UsedCSRegs;
}
}
// Compute restores required at MBB:
CSRRestore[MBB] |= (AvailOut[MBB] - AnticOut[MBB]) & availOutSucc;
// Postprocess restore placements at MBB.
// Remove the CSRs that are restored in the return blocks.
// Lest this be confusing, note that:
// CSRSave[EntryBlock] == CSRRestore[B] for all B in ReturnBlocks.
if (MBB->succ_size() && ! CSRRestore[MBB].empty()) {
if (! CSRSave[EntryBlock].empty())
CSRRestore[MBB] = CSRRestore[MBB] - CSRSave[EntryBlock];
}
placedRestores = (CSRRestore[MBB] != prevRestores[MBB]);
prevRestores[MBB] = CSRRestore[MBB];
// Remember this block for adding saves to predecessor
// blocks for multi-entry region.
if (placedRestores)
blks.push_back(MBB);
DEBUG(if (! CSRRestore[MBB].empty() && ShrinkWrapDebugging >= Iterations)
dbgs() << "RESTORE[" << getBasicBlockName(MBB) << "] = "
<< stringifyCSRegSet(CSRRestore[MBB]) << "\n");
return placedRestores;
}
/// placeSpillsAndRestores - place spills and restores of CSRs
/// used in MBBs in minimal regions that contain the uses.
///
void PEI::placeSpillsAndRestores(MachineFunction &Fn) {
CSRegBlockMap prevCSRSave;
CSRegBlockMap prevCSRRestore;
SmallVector<MachineBasicBlock*, 4> cvBlocks, ncvBlocks;
bool changed = true;
unsigned iterations = 0;
// Iterate computation of spill and restore placements in the MCFG until:
// 1. CSR use info has been fully propagated around the MCFG, and
// 2. computation of CSRSave[], CSRRestore[] reach fixed points.
while (changed) {
changed = false;
++iterations;
DEBUG(if (ShrinkWrapDebugging >= Iterations)
dbgs() << "iter " << iterations
<< " --------------------------------------------------\n");
// Calculate CSR{Save,Restore} sets using Antic, Avail on the MCFG,
// which determines the placements of spills and restores.
// Keep track of changes to spills, restores in each iteration to
// minimize the total iterations.
bool SRChanged = false;
for (MachineFunction::iterator MBBI = Fn.begin(), MBBE = Fn.end();
MBBI != MBBE; ++MBBI) {
MachineBasicBlock* MBB = MBBI;
// Place spills for CSRs in MBB.
SRChanged |= calcSpillPlacements(MBB, cvBlocks, prevCSRSave);
// Place restores for CSRs in MBB.
SRChanged |= calcRestorePlacements(MBB, cvBlocks, prevCSRRestore);
}
// Add uses of CSRs used inside loops where needed.
changed |= addUsesForTopLevelLoops(cvBlocks);
// Add uses for CSRs spilled or restored at branch, join points.
if (changed || SRChanged) {
while (! cvBlocks.empty()) {
MachineBasicBlock* MBB = cvBlocks.pop_back_val();
changed |= addUsesForMEMERegion(MBB, ncvBlocks);
}
if (! ncvBlocks.empty()) {
cvBlocks = ncvBlocks;
ncvBlocks.clear();
}
}
if (changed) {
calculateAnticAvail(Fn);
CSRSave.clear();
CSRRestore.clear();
}
}
// Check for effectiveness:
// SR0 = {r | r in CSRSave[EntryBlock], CSRRestore[RB], RB in ReturnBlocks}
// numSRReduced = |(UsedCSRegs - SR0)|, approx. SR0 by CSRSave[EntryBlock]
// Gives a measure of how many CSR spills have been moved from EntryBlock
// to minimal regions enclosing their uses.
CSRegSet notSpilledInEntryBlock = (UsedCSRegs - CSRSave[EntryBlock]);
unsigned numSRReducedThisFunc = notSpilledInEntryBlock.count();
numSRReduced += numSRReducedThisFunc;
DEBUG(if (ShrinkWrapDebugging >= BasicInfo) {
dbgs() << "-----------------------------------------------------------\n";
dbgs() << "total iterations = " << iterations << " ( "
<< Fn.getName()
<< " " << numSRReducedThisFunc
<< " " << Fn.size()
<< " )\n";
dbgs() << "-----------------------------------------------------------\n";
dumpSRSets();
dbgs() << "-----------------------------------------------------------\n";
if (numSRReducedThisFunc)
verifySpillRestorePlacement();
});
}
// Debugging methods.
#ifndef NDEBUG
/// findFastExitPath - debugging method used to detect functions
/// with at least one path from the entry block to a return block
/// directly or which has a very small number of edges.
///
void PEI::findFastExitPath() {
if (! EntryBlock)
return;
// Fina a path from EntryBlock to any return block that does not branch:
// Entry
// | ...
// v |
// B1<-----+
// |
// v
// Return
for (MachineBasicBlock::succ_iterator SI = EntryBlock->succ_begin(),
SE = EntryBlock->succ_end(); SI != SE; ++SI) {
MachineBasicBlock* SUCC = *SI;
// Assume positive, disprove existence of fast path.
HasFastExitPath = true;
// Check the immediate successors.
if (isReturnBlock(SUCC)) {
if (ShrinkWrapDebugging >= BasicInfo)
dbgs() << "Fast exit path: " << getBasicBlockName(EntryBlock)
<< "->" << getBasicBlockName(SUCC) << "\n";
break;
}
// Traverse df from SUCC, look for a branch block.
std::string exitPath = getBasicBlockName(SUCC);
for (df_iterator<MachineBasicBlock*> BI = df_begin(SUCC),
BE = df_end(SUCC); BI != BE; ++BI) {
MachineBasicBlock* SBB = *BI;
// Reject paths with branch nodes.
if (SBB->succ_size() > 1) {
HasFastExitPath = false;
break;
}
exitPath += "->" + getBasicBlockName(SBB);
}
if (HasFastExitPath) {
if (ShrinkWrapDebugging >= BasicInfo)
dbgs() << "Fast exit path: " << getBasicBlockName(EntryBlock)
<< "->" << exitPath << "\n";
break;
}
}
}
/// verifySpillRestorePlacement - check the current spill/restore
/// sets for safety. Attempt to find spills without restores or
/// restores without spills.
/// Spills: walk df from each MBB in spill set ensuring that
/// all CSRs spilled at MMBB are restored on all paths
/// from MBB to all exit blocks.
/// Restores: walk idf from each MBB in restore set ensuring that
/// all CSRs restored at MBB are spilled on all paths
/// reaching MBB.
///
void PEI::verifySpillRestorePlacement() {
unsigned numReturnBlocks = 0;
for (MachineFunction::iterator MBBI = MF->begin(), MBBE = MF->end();
MBBI != MBBE; ++MBBI) {
MachineBasicBlock* MBB = MBBI;
if (isReturnBlock(MBB) || MBB->succ_size() == 0)
++numReturnBlocks;
}
for (CSRegBlockMap::iterator BI = CSRSave.begin(),
BE = CSRSave.end(); BI != BE; ++BI) {
MachineBasicBlock* MBB = BI->first;
CSRegSet spilled = BI->second;
CSRegSet restored;
if (spilled.empty())
continue;
DEBUG(dbgs() << "SAVE[" << getBasicBlockName(MBB) << "] = "
<< stringifyCSRegSet(spilled)
<< " RESTORE[" << getBasicBlockName(MBB) << "] = "
<< stringifyCSRegSet(CSRRestore[MBB]) << "\n");
if (CSRRestore[MBB].intersects(spilled)) {
restored |= (CSRRestore[MBB] & spilled);
}
// Walk depth first from MBB to find restores of all CSRs spilled at MBB:
// we must find restores for all spills w/no intervening spills on all
// paths from MBB to all return blocks.
for (df_iterator<MachineBasicBlock*> BI = df_begin(MBB),
BE = df_end(MBB); BI != BE; ++BI) {
MachineBasicBlock* SBB = *BI;
if (SBB == MBB)
continue;
// Stop when we encounter spills of any CSRs spilled at MBB that
// have not yet been seen to be restored.
if (CSRSave[SBB].intersects(spilled) &&
!restored.contains(CSRSave[SBB] & spilled))
break;
// Collect the CSRs spilled at MBB that are restored
// at this DF successor of MBB.
if (CSRRestore[SBB].intersects(spilled))
restored |= (CSRRestore[SBB] & spilled);
// If we are at a retun block, check that the restores
// we have seen so far exhaust the spills at MBB, then
// reset the restores.
if (isReturnBlock(SBB) || SBB->succ_size() == 0) {
if (restored != spilled) {
CSRegSet notRestored = (spilled - restored);
DEBUG(dbgs() << MF->getName() << ": "
<< stringifyCSRegSet(notRestored)
<< " spilled at " << getBasicBlockName(MBB)
<< " are never restored on path to return "
<< getBasicBlockName(SBB) << "\n");
}
restored.clear();
}
}
}
// Check restore placements.
for (CSRegBlockMap::iterator BI = CSRRestore.begin(),
BE = CSRRestore.end(); BI != BE; ++BI) {
MachineBasicBlock* MBB = BI->first;
CSRegSet restored = BI->second;
CSRegSet spilled;
if (restored.empty())
continue;
DEBUG(dbgs() << "SAVE[" << getBasicBlockName(MBB) << "] = "
<< stringifyCSRegSet(CSRSave[MBB])
<< " RESTORE[" << getBasicBlockName(MBB) << "] = "
<< stringifyCSRegSet(restored) << "\n");
if (CSRSave[MBB].intersects(restored)) {
spilled |= (CSRSave[MBB] & restored);
}
// Walk inverse depth first from MBB to find spills of all
// CSRs restored at MBB:
for (idf_iterator<MachineBasicBlock*> BI = idf_begin(MBB),
BE = idf_end(MBB); BI != BE; ++BI) {
MachineBasicBlock* PBB = *BI;
if (PBB == MBB)
continue;
// Stop when we encounter restores of any CSRs restored at MBB that
// have not yet been seen to be spilled.
if (CSRRestore[PBB].intersects(restored) &&
!spilled.contains(CSRRestore[PBB] & restored))
break;
// Collect the CSRs restored at MBB that are spilled
// at this DF predecessor of MBB.
if (CSRSave[PBB].intersects(restored))
spilled |= (CSRSave[PBB] & restored);
}
if (spilled != restored) {
CSRegSet notSpilled = (restored - spilled);
DEBUG(dbgs() << MF->getName() << ": "
<< stringifyCSRegSet(notSpilled)
<< " restored at " << getBasicBlockName(MBB)
<< " are never spilled\n");
}
}
}
// Debugging print methods.
std::string PEI::getBasicBlockName(const MachineBasicBlock* MBB) {
if (!MBB)
return "";
if (MBB->getBasicBlock())
return MBB->getBasicBlock()->getName().str();
std::ostringstream name;
name << "_MBB_" << MBB->getNumber();
return name.str();
}
std::string PEI::stringifyCSRegSet(const CSRegSet& s) {
const TargetRegisterInfo* TRI = MF->getTarget().getRegisterInfo();
const std::vector<CalleeSavedInfo> CSI =
MF->getFrameInfo()->getCalleeSavedInfo();
std::ostringstream srep;
if (CSI.size() == 0) {
srep << "[]";
return srep.str();
}
srep << "[";
CSRegSet::iterator I = s.begin(), E = s.end();
if (I != E) {
unsigned reg = CSI[*I].getReg();
srep << TRI->getName(reg);
for (++I; I != E; ++I) {
reg = CSI[*I].getReg();
srep << ",";
srep << TRI->getName(reg);
}
}
srep << "]";
return srep.str();
}
void PEI::dumpSet(const CSRegSet& s) {
DEBUG(dbgs() << stringifyCSRegSet(s) << "\n");
}
void PEI::dumpUsed(MachineBasicBlock* MBB) {
DEBUG({
if (MBB)
dbgs() << "CSRUsed[" << getBasicBlockName(MBB) << "] = "
<< stringifyCSRegSet(CSRUsed[MBB]) << "\n";
});
}
void PEI::dumpAllUsed() {
for (MachineFunction::iterator MBBI = MF->begin(), MBBE = MF->end();
MBBI != MBBE; ++MBBI) {
MachineBasicBlock* MBB = MBBI;
dumpUsed(MBB);
}
}
void PEI::dumpSets(MachineBasicBlock* MBB) {
DEBUG({
if (MBB)
dbgs() << getBasicBlockName(MBB) << " | "
<< stringifyCSRegSet(CSRUsed[MBB]) << " | "
<< stringifyCSRegSet(AnticIn[MBB]) << " | "
<< stringifyCSRegSet(AnticOut[MBB]) << " | "
<< stringifyCSRegSet(AvailIn[MBB]) << " | "
<< stringifyCSRegSet(AvailOut[MBB]) << "\n";
});
}
void PEI::dumpSets1(MachineBasicBlock* MBB) {
DEBUG({
if (MBB)
dbgs() << getBasicBlockName(MBB) << " | "
<< stringifyCSRegSet(CSRUsed[MBB]) << " | "
<< stringifyCSRegSet(AnticIn[MBB]) << " | "
<< stringifyCSRegSet(AnticOut[MBB]) << " | "
<< stringifyCSRegSet(AvailIn[MBB]) << " | "
<< stringifyCSRegSet(AvailOut[MBB]) << " | "
<< stringifyCSRegSet(CSRSave[MBB]) << " | "
<< stringifyCSRegSet(CSRRestore[MBB]) << "\n";
});
}
void PEI::dumpAllSets() {
for (MachineFunction::iterator MBBI = MF->begin(), MBBE = MF->end();
MBBI != MBBE; ++MBBI) {
MachineBasicBlock* MBB = MBBI;
dumpSets1(MBB);
}
}
void PEI::dumpSRSets() {
DEBUG({
for (MachineFunction::iterator MBB = MF->begin(), E = MF->end();
MBB != E; ++MBB) {
if (!CSRSave[MBB].empty()) {
dbgs() << "SAVE[" << getBasicBlockName(MBB) << "] = "
<< stringifyCSRegSet(CSRSave[MBB]);
if (CSRRestore[MBB].empty())
dbgs() << '\n';
}
if (!CSRRestore[MBB].empty() && !CSRSave[MBB].empty())
dbgs() << " "
<< "RESTORE[" << getBasicBlockName(MBB) << "] = "
<< stringifyCSRegSet(CSRRestore[MBB]) << "\n";
}
});
}
#endif
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