llvm-6502/lib/CodeGen/LiveIntervalUnion.cpp
Andrew Trick 34fff59cad Comment typo.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@120504 91177308-0d34-0410-b5e6-96231b3b80d8
2010-11-30 23:59:50 +00:00

317 lines
11 KiB
C++

//===-- 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;
// Find the first segment in the range [SegBegin,Segments.end()) that
// intersects with LS. If no intersection is found, return the first SI
// such that SI.start >= LS.End.
//
// This logic is tied to the underlying LiveSegments data structure. For now, we
// use set::upper_bound to find the nearest starting position,
// then reverse iterate to find the first overlap.
//
// Upon entry we have SegBegin.Start < LS.End
// SegBegin |--...
// \ .
// LS ...-|
//
// After set::upper_bound, we have SI.start >= LS.start:
// SI |--...
// /
// LS |--...
//
// Assuming intervals are disjoint, if an intersection exists, it must be the
// segment found or the one immediately preceeding it. We continue reverse
// iterating to return the first overlapping segment.
LiveIntervalUnion::SegmentIter
LiveIntervalUnion::upperBound(SegmentIter SegBegin,
const LiveSegment &LS) {
assert(LS.End > SegBegin->Start && "segment iterator precondition");
// Get the next LIU segment such that segI->Start is not less than seg.Start
//
// FIXME: Once we have a B+tree, we can make good use of SegBegin as a hint to
// upper_bound. For now, we're forced to search again from the root each time.
SegmentIter SI = Segments.upper_bound(LS);
while (SI != SegBegin) {
--SI;
if (LS.Start >= SI->End)
return ++SI;
}
return SI;
}
// Merge a LiveInterval's segments. Guarantee no overlaps.
//
// After implementing B+tree, segments will be coalesced.
void LiveIntervalUnion::unify(LiveInterval &VirtReg) {
// Insert each of the virtual register's live segments into the map.
SegmentIter SegPos = Segments.begin();
for (LiveInterval::iterator VirtRegI = VirtReg.begin(),
VirtRegEnd = VirtReg.end();
VirtRegI != VirtRegEnd; ++VirtRegI ) {
LiveSegment Seg(*VirtRegI, &VirtReg);
SegPos = Segments.insert(SegPos, Seg);
assert(*SegPos == Seg && "need equal val for equal key");
#ifndef NDEBUG
// Check for overlap (inductively).
if (SegPos != Segments.begin()) {
assert(llvm::prior(SegPos)->End <= Seg.Start && "overlapping segments" );
}
SegmentIter NextPos = llvm::next(SegPos);
if (NextPos != Segments.end())
assert(Seg.End <= NextPos->Start && "overlapping segments" );
#endif // NDEBUG
}
}
// Remove a live virtual register's segments from this union.
void LiveIntervalUnion::extract(const LiveInterval &VirtReg) {
// Remove each of the virtual register's live segments from the map.
SegmentIter SegPos = Segments.begin();
for (LiveInterval::const_iterator VirtRegI = VirtReg.begin(),
VirtRegEnd = VirtReg.end();
VirtRegI != VirtRegEnd; ++VirtRegI) {
LiveSegment Seg(*VirtRegI, const_cast<LiveInterval*>(&VirtReg));
SegPos = upperBound(SegPos, Seg);
assert(SegPos != Segments.end() && "missing VirtReg segment");
Segments.erase(SegPos++);
}
}
raw_ostream& llvm::operator<<(raw_ostream& OS, const LiveSegment &LS) {
return OS << '[' << LS.Start << ',' << LS.End << ':' <<
LS.VirtReg->reg << ")";
}
void LiveSegment::dump() const {
dbgs() << *this << "\n";
}
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(),
SegEnd = Segments.end(); SI != SegEnd; ++SI) {
dbgs() << " " << *SI;
}
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) {
SegmentIter SI = Segments.begin();
SegmentIter SegEnd = Segments.end();
if (SI == SegEnd) return;
VisitedVRegs.set(SI->VirtReg->reg);
for (++SI; SI != SegEnd; ++SI) {
VisitedVRegs.set(SI->VirtReg->reg);
assert(llvm::prior(SI)->End <= SI->Start && "overlapping segments" );
}
}
#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();
SegmentIter LiveUnionEnd = LiveUnion->end();
while (IR.LiveUnionI != LiveUnionEnd) {
// 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.
while (IR.VirtRegI != VirtRegEnd &&
IR.VirtRegI->end <= IR.LiveUnionI->Start)
++IR.VirtRegI;
if (IR.VirtRegI == VirtRegEnd)
break; // Retain current (nonoverlapping) LiveUnionI
// VirtRegI may have advanced far beyond LiveUnionI,
// do a fast intersection test to "catch up"
LiveSegment Seg(*IR.VirtRegI, VirtReg);
IR.LiveUnionI = LiveUnion->upperBound(IR.LiveUnionI, Seg);
// Check if no LiveUnionI exists with VirtRegI->Start < LiveUnionI.end
if (IR.LiveUnionI == LiveUnionEnd)
break;
if (IR.LiveUnionI->Start < IR.VirtRegI->end) {
assert(overlap(*IR.VirtRegI, *IR.LiveUnionI) &&
"upperBound postcondition");
break;
}
}
if (IR.LiveUnionI == LiveUnionEnd)
IR.VirtRegI = VirtRegEnd;
}
// Find the first intersection, and cache interference info
// (retain segment iterators into both VirtReg and LiveUnion).
LiveIntervalUnion::InterferenceResult
LiveIntervalUnion::Query::firstInterference() {
if (FirstInterference != LiveIntervalUnion::InterferenceResult()) {
return FirstInterference;
}
FirstInterference = InterferenceResult(VirtReg->begin(), LiveUnion->begin());
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->End) {
if (++IR.VirtRegI == VirtReg->end())
return false;
}
else {
if (++IR.LiveUnionI == LiveUnion->end()) {
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();
SegmentIter LiveUnionEnd = LiveUnion->end();
LiveInterval *RecentInterferingVReg = NULL;
while (IR.LiveUnionI != LiveUnionEnd) {
// Advance the union's iterator to reach an unseen interfering vreg.
do {
if (IR.LiveUnionI->VirtReg == RecentInterferingVReg)
continue;
if (!isSeenInterference(IR.LiveUnionI->VirtReg))
break;
// Cache the most recent interfering vreg to bypass isSeenInterference.
RecentInterferingVReg = IR.LiveUnionI->VirtReg;
} while( ++IR.LiveUnionI != LiveUnionEnd);
if (IR.LiveUnionI == LiveUnionEnd)
break;
// Advance the VirtReg iterator until surpassing the next segment in
// LiveUnion.
//
// Note: If this is ever used for coalescing of fixed registers and we have
// a live virtual register with thousands of segments, then use upperBound
// instead.
while (IR.VirtRegI != VirtRegEnd &&
IR.VirtRegI->end <= IR.LiveUnionI->Start)
++IR.VirtRegI;
if (IR.VirtRegI == VirtRegEnd)
break;
// Check for intersection with the union's segment.
if (overlap(*IR.VirtRegI, *IR.LiveUnionI)) {
if (!IR.LiveUnionI->VirtReg->isSpillable())
SeenUnspillableVReg = true;
InterferingVRegs.push_back(IR.LiveUnionI->VirtReg);
if (InterferingVRegs.size() == MaxInterferingRegs)
return MaxInterferingRegs;
// Cache the most recent interfering vreg to bypass isSeenInterference.
RecentInterferingVReg = IR.LiveUnionI->VirtReg;
++IR.LiveUnionI;
continue;
}
// VirtRegI may have advanced far beyond LiveUnionI,
// do a fast intersection test to "catch up"
LiveSegment Seg(*IR.VirtRegI, VirtReg);
IR.LiveUnionI = LiveUnion->upperBound(IR.LiveUnionI, Seg);
}
SeenAllInterferences = true;
return InterferingVRegs.size();
}