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llvm/lib/CodeGen/ShrinkWrapping.cpp
Daniel Dunbar ce63ffb52f More migration to raw_ostream, the water has dried up around the iostream hole. 
- Some clients which used DOUT have moved to DEBUG. We are deprecating the
   "magic" DOUT behavior which avoided calling printing functions when the
   statement was disabled. In addition to being unnecessary magic, it had the
   downside of leaving code in -Asserts builds, and of hiding potentially
   unnecessary computations.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@77019 91177308-0d34-0410-b5e6-96231b3b80d8
2009-07-25 00:23:56 +00:00

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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>();
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().getDesc().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->getFunction()->getNameStr();
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) {
errs() << "Place CSR spills/restores for "
<< MF->getFunction()->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();
// Calulate 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) {
DOUT << "-----------------------------------------------------------\n";
DOUT << " Antic/Avail Sets:\n";
DOUT << "-----------------------------------------------------------\n";
DOUT << "iterations = " << iterations << "\n";
DOUT << "-----------------------------------------------------------\n";
DOUT << "MBB | USED | ANTIC_IN | ANTIC_OUT | AVAIL_IN | AVAIL_OUT\n";
DOUT << "-----------------------------------------------------------\n";
for (MachineFunction::iterator MBBI = Fn.begin(), MBBE = Fn.end();
MBBI != MBBE; ++MBBI) {
MachineBasicBlock* MBB = MBBI;
dumpSets(MBB);
}
DOUT << "-----------------------------------------------------------\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)
errs() << "DISABLED: " << Fn.getFunction()->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)
errs() << "DISABLED: " << Fn.getFunction()->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(errs() << "DISABLED: " << Fn.getFunction()->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(errs() << "DISABLED: " << Fn.getFunction()->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(errs() << "DISABLED: " << Fn.getFunction()->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({
errs() << "ENABLED: " << Fn.getFunction()->getName();
if (HasFastExitPath)
errs() << " (fast exit path)";
errs() << "\n";
if (ShrinkWrapDebugging >= BasicInfo) {
errs() << "------------------------------"
<< "-----------------------------\n";
errs() << "UsedCSRegs = " << stringifyCSRegSet(UsedCSRegs) << "\n";
if (ShrinkWrapDebugging >= Details) {
errs() << "------------------------------"
<< "-----------------------------\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)
errs() << 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)
errs() << 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)
errs() << "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)
errs() << "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)
errs() << "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)
errs() << "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) {
errs() << "-----------------------------------------------------------\n";
errs() << "total iterations = " << iterations << " ( "
<< Fn.getFunction()->getName()
<< " " << numSRReducedThisFunc
<< " " << Fn.size()
<< " )\n";
errs() << "-----------------------------------------------------------\n";
dumpSRSets();
errs() << "-----------------------------------------------------------\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)
errs() << "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)
errs() << "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;
DOUT << "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(errs() << MF->getFunction()->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;
DOUT << "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(errs() << MF->getFunction()->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()->getNameStr();
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) {
DOUT << stringifyCSRegSet(s) << "\n";
}
void PEI::dumpUsed(MachineBasicBlock* MBB) {
if (MBB) {
DOUT << "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) {
if (MBB) {
DOUT << getBasicBlockName(MBB) << " | "
<< stringifyCSRegSet(CSRUsed[MBB]) << " | "
<< stringifyCSRegSet(AnticIn[MBB]) << " | "
<< stringifyCSRegSet(AnticOut[MBB]) << " | "
<< stringifyCSRegSet(AvailIn[MBB]) << " | "
<< stringifyCSRegSet(AvailOut[MBB]) << "\n";
}
}
void PEI::dumpSets1(MachineBasicBlock* MBB) {
if (MBB) {
DOUT << 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() {
for (MachineFunction::iterator MBB = MF->begin(), E = MF->end();
MBB != E; ++MBB) {
if (! CSRSave[MBB].empty()) {
DOUT << "SAVE[" << getBasicBlockName(MBB) << "] = "
<< stringifyCSRegSet(CSRSave[MBB]);
if (CSRRestore[MBB].empty())
DOUT << "\n";
}
if (! CSRRestore[MBB].empty()) {
if (! CSRSave[MBB].empty())
DOUT << " ";
DOUT << "RESTORE[" << getBasicBlockName(MBB) << "] = "
<< stringifyCSRegSet(CSRRestore[MBB]) << "\n";
}
}
}
#endif
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