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LiveIntervalAnalysis: Cleanup handleMove{Down|Up}() functions, NFC

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These two functions are hard to reason about. This commit makes the code
more comprehensible:

- Use four distinct variables (OldIdxIn, OldIdxOut, NewIdxIn, NewIdxOut)
  with a fixed value instead of a changing iterator I that points to
  different things during the function.
- Remove the early explanation before the function in favor of more
  detailed comments inside the function. Should have more/clearer comments now
  stating which conditions are tested and which invariants hold at
  different points in the functions.

The behaviour of the code was not changed.

I hope that this will make it easier to review the changes in
http://reviews.llvm.org/D9067 which I will adapt next.

Differential Revision: http://reviews.llvm.org/D16379

llvm-svn: 258756
This commit is contained in:
Matthias Braun 2016-01-26 00:43:50 +00:00
parent 2bd89d3994
commit 7d3caf5306
2 changed files with 150 additions and 134 deletions
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6
include/llvm/CodeGen/SlotIndexes.h
View File

@ -213,6 +213,12 @@ namespace llvm {
return A.listEntry()->getIndex() < B.listEntry()->getIndex(); return A.listEntry()->getIndex() < B.listEntry()->getIndex();
} }
/// Return true if A referes to the same or an earlier instruction as B.
/// This is equivalent to !isEarlierInstr(B, A).
static bool isEarlierEqualInstr(SlotIndex A, SlotIndex B) {
return !isEarlierInstr(B, A);
}
/// Return the distance from this index to the given one. /// Return the distance from this index to the given one.
int distance(SlotIndex other) const { int distance(SlotIndex other) const {
return other.getIndex() - getIndex(); return other.getIndex() - getIndex();

278
lib/CodeGen/LiveIntervalAnalysis.cpp
View File

@ -1021,172 +1021,182 @@ private:
} }
/// Update LR to reflect an instruction has been moved downwards from OldIdx /// Update LR to reflect an instruction has been moved downwards from OldIdx
/// to NewIdx. /// to NewIdx (OldIdx < NewIdx).
///
/// 1. Live def at OldIdx:
/// Move def to NewIdx, assert endpoint after NewIdx.
///
/// 2. Live def at OldIdx, killed at NewIdx:
/// Change to dead def at NewIdx.
/// (Happens when bundling def+kill together).
///
/// 3. Dead def at OldIdx:
/// Move def to NewIdx, possibly across another live value.
///
/// 4. Def at OldIdx AND at NewIdx:
/// Remove segment [OldIdx;NewIdx) and value defined at OldIdx.
/// (Happens when bundling multiple defs together).
///
/// 5. Value read at OldIdx, killed before NewIdx:
/// Extend kill to NewIdx.
///
void handleMoveDown(LiveRange &LR) { void handleMoveDown(LiveRange &LR) {
// First look for a kill at OldIdx.
LiveRange::iterator I = LR.find(OldIdx.getBaseIndex());
LiveRange::iterator E = LR.end(); LiveRange::iterator E = LR.end();
// Is LR even live at OldIdx? // Segment going into OldIdx.
if (I == E || SlotIndex::isEarlierInstr(OldIdx, I->start)) LiveRange::iterator OldIdxIn = LR.find(OldIdx.getBaseIndex());
// No value live before or after OldIdx? Nothing to do.
if (OldIdxIn == E || SlotIndex::isEarlierInstr(OldIdx, OldIdxIn->start))
return; return;
// Handle a live-in value. LiveRange::iterator OldIdxOut;
if (!SlotIndex::isSameInstr(I->start, OldIdx)) { // Do we have a value live-in to OldIdx?
bool isKill = SlotIndex::isSameInstr(OldIdx, I->end); if (SlotIndex::isEarlierInstr(OldIdxIn->start, OldIdx)) {
// If the live-in value already extends to NewIdx, there is nothing to do. // If the live-in value already extends to NewIdx, there is nothing to do.
if (!SlotIndex::isEarlierInstr(I->end, NewIdx)) if (SlotIndex::isEarlierEqualInstr(NewIdx, OldIdxIn->end))
return; return;
// Aggressively remove all kill flags from the old kill point. // Aggressively remove all kill flags from the old kill point.
// Kill flags shouldn't be used while live intervals exist, they will be // Kill flags shouldn't be used while live intervals exist, they will be
// reinserted by VirtRegRewriter. // reinserted by VirtRegRewriter.
if (MachineInstr *KillMI = LIS.getInstructionFromIndex(I->end)) if (MachineInstr *KillMI = LIS.getInstructionFromIndex(OldIdxIn->end))
for (MIBundleOperands MO(KillMI); MO.isValid(); ++MO) for (MIBundleOperands MO(KillMI); MO.isValid(); ++MO)
if (MO->isReg() && MO->isUse()) if (MO->isReg() && MO->isUse())
MO->setIsKill(false); MO->setIsKill(false);
// Adjust I->end to reach NewIdx. This may temporarily make LR invalid by // Adjust OldIdxIn->end to reach NewIdx. This may temporarily make LR
// overlapping ranges. Case 5 above. // invalid by overlapping ranges. Case 5 above.
I->end = NewIdx.getRegSlot(I->end.isEarlyClobber()); bool isKill = SlotIndex::isSameInstr(OldIdx, OldIdxIn->end);
// If this was a kill, there may also be a def. Otherwise we're done. OldIdxIn->end = NewIdx.getRegSlot(OldIdxIn->end.isEarlyClobber());
// If this was not a kill, then there was no def and we're done.
if (!isKill) if (!isKill)
return; return;
++I;
// Did we have a Def at OldIdx?
OldIdxOut = std::next(OldIdxIn);
if (OldIdxOut == E || !SlotIndex::isSameInstr(OldIdx, OldIdxOut->start))
return;
} else {
OldIdxOut = OldIdxIn;
} }
// Check for a def at OldIdx. // If we are here then there is a Definition at OldIdx. OldIdxOut points
if (I == E || !SlotIndex::isSameInstr(OldIdx, I->start)) // to the segment starting there.
return; assert(OldIdxOut != E && SlotIndex::isSameInstr(OldIdx, OldIdxOut->start) &&
// We have a def at OldIdx. "No def?");
VNInfo *DefVNI = I->valno; VNInfo *OldIdxVNI = OldIdxOut->valno;
assert(DefVNI->def == I->start && "Inconsistent def"); assert(OldIdxVNI->def == OldIdxOut->start && "Inconsistent def");
DefVNI->def = NewIdx.getRegSlot(I->start.isEarlyClobber());
// If the defined value extends beyond NewIdx, just move the def down. // If the defined value extends beyond NewIdx, just move the beginning
// This is case 1 above. // of the segment to NewIdx.
if (SlotIndex::isEarlierInstr(NewIdx, I->end)) { SlotIndex NewIdxDef = NewIdx.getRegSlot(OldIdxOut->start.isEarlyClobber());
I->start = DefVNI->def; if (SlotIndex::isEarlierInstr(NewIdxDef, OldIdxOut->end)) {
OldIdxVNI->def = NewIdxDef;
OldIdxOut->start = OldIdxVNI->def;
return; return;
} }
// The remaining possibilities are now:
// 2. Live def at OldIdx, killed at NewIdx: isSameInstr(I->end, NewIdx). // If we are here then we have a Definition at OldIdx which ends before
// 3. Dead def at OldIdx: I->end = OldIdx.getDeadSlot(). // NewIdx. Moving across unrelated defs is not allowed; That means we either
// In either case, it is possible that there is an existing def at NewIdx. // had a dead-def at OldIdx or the OldIdxOut segment ends at NewIdx.
assert((I->end == OldIdx.getDeadSlot() || assert((OldIdxOut->end == OldIdx.getDeadSlot() ||
SlotIndex::isSameInstr(I->end, NewIdx)) && SlotIndex::isSameInstr(OldIdxOut->end, NewIdxDef)) &&
"Cannot move def below kill"); "Cannot move def below kill");
LiveRange::iterator NewI = LR.advanceTo(I, NewIdx.getRegSlot()); // Is there an existing Def at NewIdx?
if (NewI != E && SlotIndex::isSameInstr(NewI->start, NewIdx)) { LiveRange::iterator AfterNewIdx
// There is an existing def at NewIdx, case 4 above. The def at OldIdx is = LR.advanceTo(OldIdxOut, NewIdx.getRegSlot());
// coalesced into that value. if (AfterNewIdx != E &&
assert(NewI->valno != DefVNI && "Multiple defs of value?"); SlotIndex::isSameInstr(AfterNewIdx->start, NewIdxDef)) {
LR.removeValNo(DefVNI); // There is an existing def at NewIdx. The def at OldIdx is coalesced into
return; // that value.
assert(AfterNewIdx->valno != OldIdxVNI && "Multiple defs of value?");
LR.removeValNo(OldIdxVNI);
} else {
// There was no existing def at NewIdx. We need to create a dead def
// at NewIdx. Shift segments over the old OldIdxOut segment, this frees
// a new segment at the place where we want to construct the dead def.
// |- OldIdxOut -| |- X0 -| ... |- Xn -| |- AfterNewIdx -|
// => |- X0/OldIdxOut -| ... |- Xn -| |- undef/NewS. -| |- AfterNewIdx -|
assert(AfterNewIdx != OldIdxOut && "Inconsistent iterators");
std::copy(std::next(OldIdxOut), AfterNewIdx, OldIdxOut);
// We can reuse OldIdxVNI now.
LiveRange::iterator NewSegment = std::prev(AfterNewIdx);
VNInfo *NewSegmentVNI = OldIdxVNI;
NewSegmentVNI->def = NewIdxDef;
*NewSegment = LiveRange::Segment(NewIdxDef, NewIdxDef.getDeadSlot(),
NewSegmentVNI);
} }
// There was no existing def at NewIdx. Turn *I into a dead def at NewIdx.
// If the def at OldIdx was dead, we allow it to be moved across other LR
// values. The new range should be placed immediately before NewI, move any
// intermediate ranges up.
assert(NewI != I && "Inconsistent iterators");
std::copy(std::next(I), NewI, I);
*std::prev(NewI)
= LiveRange::Segment(DefVNI->def, NewIdx.getDeadSlot(), DefVNI);
} }
/// Update LR to reflect an instruction has been moved upwards from OldIdx /// Update LR to reflect an instruction has been moved upwards from OldIdx
/// to NewIdx. /// to NewIdx (NewIdx < OldIdx).
///
/// 1. Live def at OldIdx:
/// Hoist def to NewIdx.
///
/// 2. Dead def at OldIdx:
/// Hoist def+end to NewIdx, possibly move across other values.
///
/// 3. Dead def at OldIdx AND existing def at NewIdx:
/// Remove value defined at OldIdx, coalescing it with existing value.
///
/// 4. Live def at OldIdx AND existing def at NewIdx:
/// Remove value defined at NewIdx, hoist OldIdx def to NewIdx.
/// (Happens when bundling multiple defs together).
///
/// 5. Value killed at OldIdx:
/// Hoist kill to NewIdx, then scan for last kill between NewIdx and
/// OldIdx.
///
void handleMoveUp(LiveRange &LR, unsigned Reg, LaneBitmask LaneMask) { void handleMoveUp(LiveRange &LR, unsigned Reg, LaneBitmask LaneMask) {
// First look for a kill at OldIdx.
LiveRange::iterator I = LR.find(OldIdx.getBaseIndex());
LiveRange::iterator E = LR.end(); LiveRange::iterator E = LR.end();
// Is LR even live at OldIdx? // Segment going into OldIdx.
if (I == E || SlotIndex::isEarlierInstr(OldIdx, I->start)) LiveRange::iterator OldIdxIn = LR.find(OldIdx.getBaseIndex());
// No value live before or after OldIdx? Nothing to do.
if (OldIdxIn == E || SlotIndex::isEarlierInstr(OldIdx, OldIdxIn->start))
return; return;
// Handle a live-in value. LiveRange::iterator OldIdxOut;
if (!SlotIndex::isSameInstr(I->start, OldIdx)) { // Do we have a value live-in to OldIdx?
// If the live-in value isn't killed here, there is nothing to do. if (SlotIndex::isEarlierInstr(OldIdxIn->start, OldIdx)) {
if (!SlotIndex::isSameInstr(OldIdx, I->end)) // If the live-in value isn't killed here, then we have no Def at
// OldIdx, moreover the value must be live at NewIdx so there is nothing
// to do.
bool isKill = SlotIndex::isSameInstr(OldIdx, OldIdxIn->end);
if (!isKill)
return; return;
// Adjust I->end to end at NewIdx. If we are hoisting a kill above
// another use, we need to search for that use. Case 5 above. // At this point we have to move OldIdxIn->end back to the nearest
I->end = NewIdx.getRegSlot(I->end.isEarlyClobber()); // previous use but no further than NewIdx. Moreover OldIdx is a Def then
++I; // we cannot have any intermediate uses or the move would be illegal.
// If OldIdx also defines a value, there couldn't have been another use.
if (I == E || !SlotIndex::isSameInstr(I->start, OldIdx)) { OldIdxOut = std::next(OldIdxIn);
// No def, search for the new kill. // Did we have a Def at OldIdx?
if (OldIdxOut == E || !SlotIndex::isSameInstr(OldIdx, OldIdxOut->start)) {
// No def, search for the nearest previous use.
// This can never be an early clobber kill since there is no def. // This can never be an early clobber kill since there is no def.
std::prev(I)->end = findLastUseBefore(Reg, LaneMask).getRegSlot(); OldIdxIn->end = findLastUseBefore(Reg, LaneMask).getRegSlot();
// We are done if there is no def at OldIdx.
return; return;
} else {
// There can't have been any intermediate uses or defs, so move
// OldIdxIn->end to NewIdx.
OldIdxIn->end = NewIdx.getRegSlot(OldIdxIn->end.isEarlyClobber());
}
} else {
OldIdxOut = OldIdxIn;
}
// If we are here then there is a Definition at OldIdx. OldIdxOut points
// to the segment starting there.
assert(OldIdxOut != E && SlotIndex::isSameInstr(OldIdx, OldIdxOut->start) &&
"No def?");
VNInfo *OldIdxVNI = OldIdxOut->valno;
assert(OldIdxVNI->def == OldIdxOut->start && "Inconsistent def");
bool OldIdxDefIsDead = OldIdxOut->end.isDead();
// Is there an existing def at NewIdx?
SlotIndex NewIdxDef = NewIdx.getRegSlot(OldIdxOut->start.isEarlyClobber());
LiveRange::iterator NewIdxOut = LR.find(NewIdx.getRegSlot());
if (SlotIndex::isSameInstr(NewIdxOut->start, NewIdx)) {
assert(NewIdxOut->valno != OldIdxVNI &&
"Same value defined more than once?");
// If OldIdx was a dead def remove it.
if (!OldIdxDefIsDead) {
// Case 3: Remove segment starting at NewIdx and move begin of OldIdxOut
// to NewIdx so it can take its place.
OldIdxVNI->def = NewIdxDef;
OldIdxOut->start = NewIdxDef;
LR.removeValNo(NewIdxOut->valno);
} else {
// Case 4: Remove the dead def at OldIdx.
LR.removeValNo(OldIdxVNI);
}
} else {
// Previously nothing was live after NewIdx, so all we have to do now is
// move the begin of OldIdxOut to NewIdx.
if (!OldIdxDefIsDead) {
// Leave the end point of a live def.
OldIdxVNI->def = NewIdxDef;
OldIdxOut->start = NewIdxDef;
} else {
// OldIdxVNI is a dead def. It may have been moved across other values
// in LR, so move OldIdxOut up to NewIdxOut. Slide [NewIdxOut;OldIdxOut)
// down one position.
// |- X0/NewIdxOut -| ... |- Xn-1 -| |- Xn/OldIdxOut -| |- next - |
// => |- undef/NewIdxOut -| |- X0 -| ... |- Xn-1 -| |- next -|
std::copy_backward(NewIdxOut, OldIdxOut, std::next(OldIdxOut));
// OldIdxVNI can be reused now to build a new dead def segment.
LiveRange::iterator NewSegment = NewIdxOut;
VNInfo *NewSegmentVNI = OldIdxVNI;
*NewSegment = LiveRange::Segment(NewIdxDef, NewIdxDef.getDeadSlot(),
NewSegmentVNI);
NewSegmentVNI->def = NewIdxDef;
} }
} }
// Now deal with the def at OldIdx.
assert(I != E && SlotIndex::isSameInstr(I->start, OldIdx) && "No def?");
VNInfo *DefVNI = I->valno;
assert(DefVNI->def == I->start && "Inconsistent def");
DefVNI->def = NewIdx.getRegSlot(I->start.isEarlyClobber());
// Check for an existing def at NewIdx.
LiveRange::iterator NewI = LR.find(NewIdx.getRegSlot());
if (SlotIndex::isSameInstr(NewI->start, NewIdx)) {
assert(NewI->valno != DefVNI && "Same value defined more than once?");
// There is an existing def at NewIdx.
if (I->end.isDead()) {
// Case 3: Remove the dead def at OldIdx.
LR.removeValNo(DefVNI);
return;
}
// Case 4: Replace def at NewIdx with live def at OldIdx.
I->start = DefVNI->def;
LR.removeValNo(NewI->valno);
return;
}
// There is no existing def at NewIdx. Hoist DefVNI.
if (!I->end.isDead()) {
// Leave the end point of a live def.
I->start = DefVNI->def;
return;
}
// DefVNI is a dead def. It may have been moved across other values in LR,
// so move I up to NewI. Slide [NewI;I) down one position.
std::copy_backward(NewI, I, std::next(I));
*NewI = LiveRange::Segment(DefVNI->def, NewIdx.getDeadSlot(), DefVNI);
} }
void updateRegMaskSlots() { void updateRegMaskSlots() {