[llvm] r258756 - LiveIntervalAnalysis: Cleanup handleMove{Down|Up}() functions, NFC
Matthias Braun via llvm-commits
llvm-commits at lists.llvm.org
Mon Jan 25 16:43:50 PST 2016
Author: matze
Date: Mon Jan 25 18:43:50 2016
New Revision: 258756
URL: http://llvm.org/viewvc/llvm-project?rev=258756&view=rev
Log:
LiveIntervalAnalysis: Cleanup handleMove{Down|Up}() functions, NFC
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
Modified:
llvm/trunk/include/llvm/CodeGen/SlotIndexes.h
llvm/trunk/lib/CodeGen/LiveIntervalAnalysis.cpp
Modified: llvm/trunk/include/llvm/CodeGen/SlotIndexes.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/CodeGen/SlotIndexes.h?rev=258756&r1=258755&r2=258756&view=diff
==============================================================================
--- llvm/trunk/include/llvm/CodeGen/SlotIndexes.h (original)
+++ llvm/trunk/include/llvm/CodeGen/SlotIndexes.h Mon Jan 25 18:43:50 2016
@@ -213,6 +213,12 @@ namespace llvm {
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.
int distance(SlotIndex other) const {
return other.getIndex() - getIndex();
Modified: llvm/trunk/lib/CodeGen/LiveIntervalAnalysis.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/LiveIntervalAnalysis.cpp?rev=258756&r1=258755&r2=258756&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/LiveIntervalAnalysis.cpp (original)
+++ llvm/trunk/lib/CodeGen/LiveIntervalAnalysis.cpp Mon Jan 25 18:43:50 2016
@@ -1021,172 +1021,182 @@ private:
}
/// Update LR to reflect an instruction has been moved downwards from OldIdx
- /// to 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.
- ///
+ /// to NewIdx (OldIdx < NewIdx).
void handleMoveDown(LiveRange &LR) {
- // First look for a kill at OldIdx.
- LiveRange::iterator I = LR.find(OldIdx.getBaseIndex());
LiveRange::iterator E = LR.end();
- // Is LR even live at OldIdx?
- if (I == E || SlotIndex::isEarlierInstr(OldIdx, I->start))
+ // Segment going into OldIdx.
+ 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;
- // Handle a live-in value.
- if (!SlotIndex::isSameInstr(I->start, OldIdx)) {
- bool isKill = SlotIndex::isSameInstr(OldIdx, I->end);
+ LiveRange::iterator OldIdxOut;
+ // Do we have a value live-in to OldIdx?
+ if (SlotIndex::isEarlierInstr(OldIdxIn->start, OldIdx)) {
// 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;
// Aggressively remove all kill flags from the old kill point.
// Kill flags shouldn't be used while live intervals exist, they will be
// reinserted by VirtRegRewriter.
- if (MachineInstr *KillMI = LIS.getInstructionFromIndex(I->end))
+ if (MachineInstr *KillMI = LIS.getInstructionFromIndex(OldIdxIn->end))
for (MIBundleOperands MO(KillMI); MO.isValid(); ++MO)
if (MO->isReg() && MO->isUse())
MO->setIsKill(false);
- // Adjust I->end to reach NewIdx. This may temporarily make LR invalid by
- // overlapping ranges. Case 5 above.
- I->end = NewIdx.getRegSlot(I->end.isEarlyClobber());
- // If this was a kill, there may also be a def. Otherwise we're done.
+ // Adjust OldIdxIn->end to reach NewIdx. This may temporarily make LR
+ // invalid by overlapping ranges. Case 5 above.
+ bool isKill = SlotIndex::isSameInstr(OldIdx, OldIdxIn->end);
+ OldIdxIn->end = NewIdx.getRegSlot(OldIdxIn->end.isEarlyClobber());
+ // If this was not a kill, then there was no def and we're done.
if (!isKill)
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 (I == E || !SlotIndex::isSameInstr(OldIdx, I->start))
- return;
- // We have a def at OldIdx.
- VNInfo *DefVNI = I->valno;
- assert(DefVNI->def == I->start && "Inconsistent def");
- DefVNI->def = NewIdx.getRegSlot(I->start.isEarlyClobber());
- // If the defined value extends beyond NewIdx, just move the def down.
- // This is case 1 above.
- if (SlotIndex::isEarlierInstr(NewIdx, I->end)) {
- I->start = DefVNI->def;
+ // 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");
+
+ // If the defined value extends beyond NewIdx, just move the beginning
+ // of the segment to NewIdx.
+ SlotIndex NewIdxDef = NewIdx.getRegSlot(OldIdxOut->start.isEarlyClobber());
+ if (SlotIndex::isEarlierInstr(NewIdxDef, OldIdxOut->end)) {
+ OldIdxVNI->def = NewIdxDef;
+ OldIdxOut->start = OldIdxVNI->def;
return;
}
- // The remaining possibilities are now:
- // 2. Live def at OldIdx, killed at NewIdx: isSameInstr(I->end, NewIdx).
- // 3. Dead def at OldIdx: I->end = OldIdx.getDeadSlot().
- // In either case, it is possible that there is an existing def at NewIdx.
- assert((I->end == OldIdx.getDeadSlot() ||
- SlotIndex::isSameInstr(I->end, NewIdx)) &&
+
+ // If we are here then we have a Definition at OldIdx which ends before
+ // NewIdx. Moving across unrelated defs is not allowed; That means we either
+ // had a dead-def at OldIdx or the OldIdxOut segment ends at NewIdx.
+ assert((OldIdxOut->end == OldIdx.getDeadSlot() ||
+ SlotIndex::isSameInstr(OldIdxOut->end, NewIdxDef)) &&
"Cannot move def below kill");
- LiveRange::iterator NewI = LR.advanceTo(I, NewIdx.getRegSlot());
- if (NewI != E && SlotIndex::isSameInstr(NewI->start, NewIdx)) {
- // There is an existing def at NewIdx, case 4 above. The def at OldIdx is
- // coalesced into that value.
- assert(NewI->valno != DefVNI && "Multiple defs of value?");
- LR.removeValNo(DefVNI);
- return;
+ // Is there an existing Def at NewIdx?
+ LiveRange::iterator AfterNewIdx
+ = LR.advanceTo(OldIdxOut, NewIdx.getRegSlot());
+ if (AfterNewIdx != E &&
+ SlotIndex::isSameInstr(AfterNewIdx->start, NewIdxDef)) {
+ // There is an existing def at NewIdx. The def at OldIdx is coalesced into
+ // 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
- /// to NewIdx.
- ///
- /// 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.
- ///
+ /// to NewIdx (NewIdx < OldIdx).
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();
- // Is LR even live at OldIdx?
- if (I == E || SlotIndex::isEarlierInstr(OldIdx, I->start))
+ // Segment going into OldIdx.
+ 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;
- // Handle a live-in value.
- if (!SlotIndex::isSameInstr(I->start, OldIdx)) {
- // If the live-in value isn't killed here, there is nothing to do.
- if (!SlotIndex::isSameInstr(OldIdx, I->end))
+ LiveRange::iterator OldIdxOut;
+ // Do we have a value live-in to OldIdx?
+ if (SlotIndex::isEarlierInstr(OldIdxIn->start, OldIdx)) {
+ // 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;
- // 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.
- I->end = NewIdx.getRegSlot(I->end.isEarlyClobber());
- ++I;
- // If OldIdx also defines a value, there couldn't have been another use.
- if (I == E || !SlotIndex::isSameInstr(I->start, OldIdx)) {
- // No def, search for the new kill.
+
+ // At this point we have to move OldIdxIn->end back to the nearest
+ // previous use but no further than NewIdx. Moreover OldIdx is a Def then
+ // we cannot have any intermediate uses or the move would be illegal.
+
+ OldIdxOut = std::next(OldIdxIn);
+ // 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.
- 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;
+ } 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;
}
- // 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;
+ // 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;
}
- // 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() {
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