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Calculate dead instructions when a live interval is created.

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This gets us closer to being able to remove LiveVariables entirely which is where dead instructions are currently tagged as such.

Reviewed by Jakob Olesen

llvm-svn: 210132
This commit is contained in:
Pete Cooper 2014-06-03 22:42:10 +00:00
parent 8de08a9627
commit 7223557752
2 changed files with 29 additions and 9 deletions
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11
llvm/include/llvm/CodeGen/LiveIntervalAnalysis.h
View File

@ -155,6 +155,17 @@ namespace llvm {
bool shrinkToUses(LiveInterval *li,
SmallVectorImpl<MachineInstr*> *dead = nullptr);
/// \brief Walk the values in the given interval and compute which ones
/// are dead. Dead values are not deleted, however:
/// - Dead PHIDef values are marked as unused.
/// - New dead machine instructions are added to the dead vector.
/// - CanSeparate is set to true if the interval may have been separated
/// into multiple connected components.
void computeDeadValues(LiveInterval *li,
LiveRange &LR,
bool *CanSeparate,
SmallVectorImpl<MachineInstr*> *dead);
/// extendToIndices - Extend the live range of LI to reach all points in
/// Indices. The points in the Indices array must be jointly dominated by
/// existing defs in LI. PHI-defs are added as needed to maintain SSA form.

27
llvm/lib/CodeGen/LiveIntervalAnalysis.cpp
View File

@ -186,6 +186,7 @@ void LiveIntervals::computeVirtRegInterval(LiveInterval &LI) {
LRCalc->reset(MF, getSlotIndexes(), DomTree, &getVNInfoAllocator());
LRCalc->createDeadDefs(LI);
LRCalc->extendToUses(LI);
computeDeadValues(&LI, LI, nullptr, nullptr);
}
void LiveIntervals::computeVirtRegs() {
@ -412,21 +413,34 @@ bool LiveIntervals::shrinkToUses(LiveInterval *li,
// Handle dead values.
bool CanSeparate = false;
computeDeadValues(li, NewLR, &CanSeparate, dead);
// Move the trimmed segments back.
li->segments.swap(NewLR.segments);
DEBUG(dbgs() << "Shrunk: " << *li << '\n');
return CanSeparate;
}
void LiveIntervals::computeDeadValues(LiveInterval *li,
LiveRange &LR,
bool *CanSeparate,
SmallVectorImpl<MachineInstr*> *dead) {
for (LiveInterval::vni_iterator I = li->vni_begin(), E = li->vni_end();
I != E; ++I) {
VNInfo *VNI = *I;
if (VNI->isUnused())
continue;
LiveRange::iterator LRI = NewLR.FindSegmentContaining(VNI->def);
assert(LRI != NewLR.end() && "Missing segment for PHI");
LiveRange::iterator LRI = LR.FindSegmentContaining(VNI->def);
assert(LRI != LR.end() && "Missing segment for PHI");
if (LRI->end != VNI->def.getDeadSlot())
continue;
if (VNI->isPHIDef()) {
// This is a dead PHI. Remove it.
VNI->markUnused();
NewLR.removeSegment(LRI->start, LRI->end);
LR.removeSegment(LRI->start, LRI->end);
DEBUG(dbgs() << "Dead PHI at " << VNI->def << " may separate interval\n");
CanSeparate = true;
if (CanSeparate)
*CanSeparate = true;
} else {
// This is a dead def. Make sure the instruction knows.
MachineInstr *MI = getInstructionFromIndex(VNI->def);
@ -438,11 +452,6 @@ bool LiveIntervals::shrinkToUses(LiveInterval *li,
}
}
}
// Move the trimmed segments back.
li->segments.swap(NewLR.segments);
DEBUG(dbgs() << "Shrunk: " << *li << '\n');
return CanSeparate;
}
void LiveIntervals::extendToIndices(LiveRange &LR,