llvm-6502/lib/CodeGen/LiveIntervalUnion.cpp

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//===-- LiveIntervalUnion.cpp - Live interval union data structure --------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// LiveIntervalUnion represents a coalesced set of live intervals. This may be
// used during coalescing to represent a congruence class, or during register
// allocation to model liveness of a physical register.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "regalloc"
#include "LiveIntervalUnion.h"
#include "llvm/ADT/SparseBitVector.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
using namespace llvm;
// Merge a LiveInterval's segments. Guarantee no overlaps.
void LiveIntervalUnion::unify(LiveInterval &VirtReg) {
if (VirtReg.empty())
return;
// Insert each of the virtual register's live segments into the map.
LiveInterval::iterator RegPos = VirtReg.begin();
LiveInterval::iterator RegEnd = VirtReg.end();
SegmentIter SegPos = Segments.find(RegPos->start);
for (;;) {
SegPos.insert(RegPos->start, RegPos->end, &VirtReg);
if (++RegPos == RegEnd)
return;
SegPos.advanceTo(RegPos->start);
}
}
// Remove a live virtual register's segments from this union.
void LiveIntervalUnion::extract(LiveInterval &VirtReg) {
if (VirtReg.empty())
return;
// Remove each of the virtual register's live segments from the map.
LiveInterval::iterator RegPos = VirtReg.begin();
LiveInterval::iterator RegEnd = VirtReg.end();
SegmentIter SegPos = Segments.find(RegPos->start);
for (;;) {
assert(SegPos.value() == &VirtReg && "Inconsistent LiveInterval");
SegPos.erase();
if (!SegPos.valid())
return;
// Skip all segments that may have been coalesced.
RegPos = VirtReg.advanceTo(RegPos, SegPos.start());
if (RegPos == RegEnd)
return;
SegPos.advanceTo(RegPos->start);
}
}
void
LiveIntervalUnion::print(raw_ostream &OS,
const AbstractRegisterDescription *RegDesc) const {
OS << "LIU ";
if (RegDesc != NULL)
OS << RegDesc->getName(RepReg);
else {
OS << RepReg;
}
for (LiveSegments::const_iterator SI = Segments.begin(); SI.valid(); ++SI)
dbgs() << " [" << SI.start() << ' ' << SI.stop() << "):%reg"
<< SI.value()->reg;
OS << "\n";
}
void LiveIntervalUnion::dump(const AbstractRegisterDescription *RegDesc) const {
print(dbgs(), RegDesc);
}
#ifndef NDEBUG
// Verify the live intervals in this union and add them to the visited set.
void LiveIntervalUnion::verify(LiveVirtRegBitSet& VisitedVRegs) {
for (SegmentIter SI = Segments.begin(); SI.valid(); ++SI)
VisitedVRegs.set(SI.value()->reg);
}
#endif //!NDEBUG
// Private interface accessed by Query.
//
// Find a pair of segments that intersect, one in the live virtual register
// (LiveInterval), and the other in this LiveIntervalUnion. The caller (Query)
// is responsible for advancing the LiveIntervalUnion segments to find a
// "notable" intersection, which requires query-specific logic.
//
// This design assumes only a fast mechanism for intersecting a single live
// virtual register segment with a set of LiveIntervalUnion segments. This may
// be ok since most virtual registers have very few segments. If we had a data
// structure that optimizd MxN intersection of segments, then we would bypass
// the loop that advances within the LiveInterval.
//
// If no intersection exists, set VirtRegI = VirtRegEnd, and set SI to the first
// segment whose start point is greater than LiveInterval's end point.
//
// Assumes that segments are sorted by start position in both
// LiveInterval and LiveSegments.
void LiveIntervalUnion::Query::findIntersection(InterferenceResult &IR) const {
// Search until reaching the end of the LiveUnion segments.
LiveInterval::iterator VirtRegEnd = VirtReg->end();
if (IR.VirtRegI == VirtRegEnd)
return;
while (IR.LiveUnionI.valid()) {
// Slowly advance the live virtual reg iterator until we surpass the next
// segment in LiveUnion.
//
// Note: If this is ever used for coalescing of fixed registers and we have
// a live vreg with thousands of segments, then change this code to use
// upperBound instead.
IR.VirtRegI = VirtReg->advanceTo(IR.VirtRegI, IR.LiveUnionI.start());
if (IR.VirtRegI == VirtRegEnd)
break; // Retain current (nonoverlapping) LiveUnionI
// VirtRegI may have advanced far beyond LiveUnionI, catch up.
IR.LiveUnionI.advanceTo(IR.VirtRegI->start);
// Check if no LiveUnionI exists with VirtRegI->Start < LiveUnionI.end
if (!IR.LiveUnionI.valid())
break;
if (IR.LiveUnionI.start() < IR.VirtRegI->end) {
assert(overlap(*IR.VirtRegI, IR.LiveUnionI) &&
"upperBound postcondition");
break;
}
}
if (!IR.LiveUnionI.valid())
IR.VirtRegI = VirtRegEnd;
}
// Find the first intersection, and cache interference info
// (retain segment iterators into both VirtReg and LiveUnion).
const LiveIntervalUnion::InterferenceResult &
LiveIntervalUnion::Query::firstInterference() {
if (CheckedFirstInterference)
return FirstInterference;
CheckedFirstInterference = true;
InterferenceResult &IR = FirstInterference;
// Quickly skip interference check for empty sets.
if (VirtReg->empty() || LiveUnion->empty()) {
IR.VirtRegI = VirtReg->end();
} else if (VirtReg->beginIndex() < LiveUnion->startIndex()) {
// VirtReg starts first, perform double binary search.
IR.VirtRegI = VirtReg->find(LiveUnion->startIndex());
if (IR.VirtRegI != VirtReg->end())
IR.LiveUnionI = LiveUnion->find(IR.VirtRegI->start);
} else {
// LiveUnion starts first, perform double binary search.
IR.LiveUnionI = LiveUnion->find(VirtReg->beginIndex());
if (IR.LiveUnionI.valid())
IR.VirtRegI = VirtReg->find(IR.LiveUnionI.start());
else
IR.VirtRegI = VirtReg->end();
}
findIntersection(FirstInterference);
return FirstInterference;
}
// Treat the result as an iterator and advance to the next interfering pair
// of segments. This is a plain iterator with no filter.
bool LiveIntervalUnion::Query::nextInterference(InterferenceResult &IR) const {
assert(isInterference(IR) && "iteration past end of interferences");
// Advance either the VirtReg or LiveUnion segment to ensure that we visit all
// unique overlapping pairs.
if (IR.VirtRegI->end < IR.LiveUnionI.stop()) {
if (++IR.VirtRegI == VirtReg->end())
return false;
}
else {
if (!(++IR.LiveUnionI).valid()) {
IR.VirtRegI = VirtReg->end();
return false;
}
}
// Short-circuit findIntersection() if possible.
if (overlap(*IR.VirtRegI, IR.LiveUnionI))
return true;
// Find the next intersection.
findIntersection(IR);
return isInterference(IR);
}
// Scan the vector of interfering virtual registers in this union. Assume it's
// quite small.
bool LiveIntervalUnion::Query::isSeenInterference(LiveInterval *VirtReg) const {
SmallVectorImpl<LiveInterval*>::const_iterator I =
std::find(InterferingVRegs.begin(), InterferingVRegs.end(), VirtReg);
return I != InterferingVRegs.end();
}
// Count the number of virtual registers in this union that interfere with this
// query's live virtual register.
//
// The number of times that we either advance IR.VirtRegI or call
// LiveUnion.upperBound() will be no more than the number of holes in
// VirtReg. So each invocation of collectInterferingVRegs() takes
// time proportional to |VirtReg Holes| * time(LiveUnion.upperBound()).
//
// For comments on how to speed it up, see Query::findIntersection().
unsigned LiveIntervalUnion::Query::
collectInterferingVRegs(unsigned MaxInterferingRegs) {
InterferenceResult IR = firstInterference();
LiveInterval::iterator VirtRegEnd = VirtReg->end();
LiveInterval *RecentInterferingVReg = NULL;
while (IR.LiveUnionI.valid()) {
// Advance the union's iterator to reach an unseen interfering vreg.
do {
if (IR.LiveUnionI.value() == RecentInterferingVReg)
continue;
if (!isSeenInterference(IR.LiveUnionI.value()))
break;
// Cache the most recent interfering vreg to bypass isSeenInterference.
RecentInterferingVReg = IR.LiveUnionI.value();
} while ((++IR.LiveUnionI).valid());
if (!IR.LiveUnionI.valid())
break;
// Advance the VirtReg iterator until surpassing the next segment in
// LiveUnion.
IR.VirtRegI = VirtReg->advanceTo(IR.VirtRegI, IR.LiveUnionI.start());
if (IR.VirtRegI == VirtRegEnd)
break;
// Check for intersection with the union's segment.
if (overlap(*IR.VirtRegI, IR.LiveUnionI)) {
if (!IR.LiveUnionI.value()->isSpillable())
SeenUnspillableVReg = true;
InterferingVRegs.push_back(IR.LiveUnionI.value());
if (InterferingVRegs.size() == MaxInterferingRegs)
return MaxInterferingRegs;
// Cache the most recent interfering vreg to bypass isSeenInterference.
RecentInterferingVReg = IR.LiveUnionI.value();
++IR.LiveUnionI;
continue;
}
// VirtRegI may have advanced far beyond LiveUnionI,
// do a fast intersection test to "catch up"
IR.LiveUnionI.advanceTo(IR.VirtRegI->start);
}
SeenAllInterferences = true;
return InterferingVRegs.size();
}