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Create two BlockInfo entries when a live range is discontinuous through a block. 

Delete the Kill and Def markers in BlockInfo. They are no longer
necessary when BlockInfo describes a continuous live range.

This only affects the relatively rare kind of basic block where a live
range looks like this:

 |---x   o---|

Now live range splitting can pretend that it is looking at two blocks:

 |---x
         o---|

This allows the code to be simplified a bit.

llvm-svn: 132245
This commit is contained in:
Jakob Stoklund Olesen 2011-05-28 02:33:00 +00:00
parent 5cc91b2611
commit fd3f71ef3a
3 changed files with 72 additions and 56 deletions
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20
llvm/lib/CodeGen/RegAllocGreedy.cpp
View File

@ -552,7 +552,7 @@ bool RAGreedy::addSplitConstraints(InterferenceCache::Cursor Intf,
BC.Entry = SpillPlacement::MustSpill, ++Ins;
else if (Intf.first() < BI.FirstUse)
BC.Entry = SpillPlacement::PrefSpill, ++Ins;
else if (Intf.first() < (BI.LiveThrough ? BI.LastUse : BI.Kill))
else if (Intf.first() < BI.LastUse)
++Ins;
}
@ -562,7 +562,7 @@ bool RAGreedy::addSplitConstraints(InterferenceCache::Cursor Intf,
BC.Exit = SpillPlacement::MustSpill, ++Ins;
else if (Intf.last() > BI.LastUse)
BC.Exit = SpillPlacement::PrefSpill, ++Ins;
else if (Intf.last() > (BI.LiveThrough ? BI.FirstUse : BI.Def))
else if (Intf.last() > BI.FirstUse)
++Ins;
}
@ -811,7 +811,7 @@ void RAGreedy::splitAroundRegion(LiveInterval &VirtReg,
DEBUG(dbgs() << ", no interference");
if (!BI.LiveThrough) {
DEBUG(dbgs() << ", not live-through.\n");
SE->useIntv(SE->enterIntvBefore(BI.Def), Stop);
SE->useIntv(SE->enterIntvBefore(BI.FirstUse), Stop);
continue;
}
if (!RegIn) {
@ -828,10 +828,10 @@ void RAGreedy::splitAroundRegion(LiveInterval &VirtReg,
// Block has interference.
DEBUG(dbgs() << ", interference to " << Intf.last());
if (!BI.LiveThrough && Intf.last() <= BI.Def) {
if (!BI.LiveThrough && Intf.last() <= BI.FirstUse) {
// The interference doesn't reach the outgoing segment.
DEBUG(dbgs() << " doesn't affect def from " << BI.Def << '\n');
SE->useIntv(BI.Def, Stop);
DEBUG(dbgs() << " doesn't affect def from " << BI.FirstUse << '\n');
SE->useIntv(BI.FirstUse, Stop);
continue;
}
@ -887,7 +887,7 @@ void RAGreedy::splitAroundRegion(LiveInterval &VirtReg,
DEBUG(dbgs() << ", no interference");
if (!BI.LiveThrough) {
DEBUG(dbgs() << ", killed in block.\n");
SE->useIntv(Start, SE->leaveIntvAfter(BI.Kill));
SE->useIntv(Start, SE->leaveIntvAfter(BI.LastUse));
continue;
}
if (!RegOut) {
@ -920,10 +920,10 @@ void RAGreedy::splitAroundRegion(LiveInterval &VirtReg,
// Block has interference.
DEBUG(dbgs() << ", interference from " << Intf.first());
if (!BI.LiveThrough && Intf.first() >= BI.Kill) {
if (!BI.LiveThrough && Intf.first() >= BI.LastUse) {
// The interference doesn't reach the outgoing segment.
DEBUG(dbgs() << " doesn't affect kill at " << BI.Kill << '\n');
SE->useIntv(Start, BI.Kill);
DEBUG(dbgs() << " doesn't affect kill at " << BI.LastUse << '\n');
SE->useIntv(Start, BI.LastUse);
continue;
}

87
llvm/lib/CodeGen/SplitKit.cpp
View File

@ -145,7 +145,7 @@ void SplitAnalysis::analyzeUses() {
/// where CurLI is live.
bool SplitAnalysis::calcLiveBlockInfo() {
ThroughBlocks.resize(MF.getNumBlockIDs());
NumThroughBlocks = 0;
NumThroughBlocks = NumGapBlocks = 0;
if (CurLI->empty())
return true;
@ -164,55 +164,62 @@ bool SplitAnalysis::calcLiveBlockInfo() {
SlotIndex Start, Stop;
tie(Start, Stop) = LIS.getSlotIndexes()->getMBBRange(BI.MBB);
// LVI is the first live segment overlapping MBB.
BI.LiveIn = LVI->start <= Start;
if (!BI.LiveIn)
BI.Def = LVI->start;
// Find the first and last uses in the block.
bool Uses = UseI != UseE && *UseI < Stop;
if (Uses) {
// If the block contains no uses, the range must be live through. At one
// point, SimpleRegisterCoalescing could create dangling ranges that ended
// mid-block.
if (UseI == UseE || *UseI >= Stop) {
++NumThroughBlocks;
ThroughBlocks.set(BI.MBB->getNumber());
// The range shouldn't end mid-block if there are no uses. This shouldn't
// happen.
if (LVI->end < Stop)
return false;
} else {
// This block has uses. Find the first and last uses in the block.
BI.FirstUse = *UseI;
assert(BI.FirstUse >= Start);
do ++UseI;
while (UseI != UseE && *UseI < Stop);
BI.LastUse = UseI[-1];
assert(BI.LastUse < Stop);
}
// Look for gaps in the live range.
bool hasGap = false;
BI.LiveOut = true;
while (LVI->end < Stop) {
SlotIndex LastStop = LVI->end;
if (++LVI == LVE || LVI->start >= Stop) {
BI.Kill = LastStop;
BI.LiveOut = false;
break;
}
if (LastStop < LVI->start) {
hasGap = true;
BI.Kill = LastStop;
BI.Def = LVI->start;
}
}
// LVI is the first live segment overlapping MBB.
BI.LiveIn = LVI->start <= Start;
// Don't set LiveThrough when the block has a gap.
BI.LiveThrough = !hasGap && BI.LiveIn && BI.LiveOut;
if (Uses)
// Look for gaps in the live range.
BI.LiveOut = true;
while (LVI->end < Stop) {
SlotIndex LastStop = LVI->end;
if (++LVI == LVE || LVI->start >= Stop) {
BI.LiveOut = false;
break;
}
if (LastStop < LVI->start) {
// There is a gap in the live range. Create duplicate entries for the
// live-in snippet and the live-out snippet.
++NumGapBlocks;
// Push the Live-in part.
BI.LiveThrough = false;
BI.LiveOut = false;
UseBlocks.push_back(BI);
UseBlocks.back().LastUse = LastStop;
// Set up BI for the live-out part.
BI.LiveIn = false;
BI.LiveOut = true;
BI.FirstUse = LVI->start;
}
}
// Don't set LiveThrough when the block has a gap.
BI.LiveThrough = BI.LiveIn && BI.LiveOut;
UseBlocks.push_back(BI);
else {
++NumThroughBlocks;
ThroughBlocks.set(BI.MBB->getNumber());
}
// FIXME: This should never happen. The live range stops or starts without a
// corresponding use. An earlier pass did something wrong.
if (!BI.LiveThrough && !Uses)
return false;
// LVI is now at LVE or LVI->end >= Stop.
if (LVI == LVE)
break;
// LVI is now at LVE or LVI->end >= Stop.
if (LVI == LVE)
break;
}
// Live segment ends exactly at Stop. Move to the next segment.
if (LVI->end == Stop && ++LVI == LVE)

21
llvm/lib/CodeGen/SplitKit.h
View File

@ -63,17 +63,22 @@ public:
/// 1. | o---x | Internal to block. Variable is only live in this block.
/// 2. |---x | Live-in, kill.
/// 3. | o---| Def, live-out.
/// 4. |---x o---| Live-in, kill, def, live-out.
/// 4. |---x o---| Live-in, kill, def, live-out. Counted by NumGapBlocks.
/// 5. |---o---o---| Live-through with uses or defs.
/// 6. |-----------| Live-through without uses. Transparent.
/// 6. |-----------| Live-through without uses. Counted by NumThroughBlocks.
///
/// Two BlockInfo entries are created for template 4. One for the live-in
/// segment, and one for the live-out segment. These entries look as if the
/// block were split in the middle where the live range isn't live.
///
/// Live-through blocks without any uses don't get BlockInfo entries. They
/// are simply listed in ThroughBlocks instead.
///
struct BlockInfo {
MachineBasicBlock *MBB;
SlotIndex FirstUse; ///< First instr using current reg.
SlotIndex LastUse; ///< Last instr using current reg.
SlotIndex Kill; ///< Interval end point inside block.
SlotIndex Def; ///< Interval start point inside block.
bool LiveThrough; ///< Live in whole block (Templ 5. or 6. above).
bool LiveThrough; ///< Live in whole block (Templ 5. above).
bool LiveIn; ///< Current reg is live in.
bool LiveOut; ///< Current reg is live out.
};
@ -91,6 +96,10 @@ private:
/// UseBlocks - Blocks where CurLI has uses.
SmallVector<BlockInfo, 8> UseBlocks;
/// NumGapBlocks - Number of duplicate entries in UseBlocks for blocks where
/// the live range has a gap.
unsigned NumGapBlocks;
/// ThroughBlocks - Block numbers where CurLI is live through without uses.
BitVector ThroughBlocks;
@ -160,7 +169,7 @@ public:
/// getNumLiveBlocks - Return the number of blocks where CurLI is live.
unsigned getNumLiveBlocks() const {
return getUseBlocks().size() + getNumThroughBlocks();
return getUseBlocks().size() - NumGapBlocks + getNumThroughBlocks();
}
/// countLiveBlocks - Return the number of blocks where li is live. This is