[nfc][regalloc] const LiveIntervals within the allocator

Once built, LiveIntervals are immutable. This patch captures that.

Differential Revision: https://reviews.llvm.org/D118918

1 files changed, 34 insertions, 19 deletions

diff --git a/llvm/lib/CodeGen/SplitKit.cpp b/llvm/lib/CodeGen/SplitKit.cpp
index 7f9518e..3851a0c 100644
--- a/llvm/lib/CodeGen/SplitKit.cpp
+++ b/llvm/lib/CodeGen/SplitKit.cpp
@@ -389,17 +389,34 @@ LLVM_DUMP_METHOD void SplitEditor::dump() const {
 }
 #endif
 
-LiveInterval::SubRange &SplitEditor::getSubRangeForMaskExact(LaneBitmask LM,
-                                                             LiveInterval &LI) {
-  for (LiveInterval::SubRange &S : LI.subranges())
+/// Find a subrange corresponding to the exact lane mask @p LM in the live
+/// interval @p LI. The interval @p LI is assumed to contain such a subrange.
+/// This function is used to find corresponding subranges between the
+/// original interval and the new intervals.
+template <typename T> auto &getSubrangeImpl(LaneBitmask LM, T &LI) {
+  for (auto &S : LI.subranges())
     if (S.LaneMask == LM)
       return S;
   llvm_unreachable("SubRange for this mask not found");
 }
 
-LiveInterval::SubRange &SplitEditor::getSubRangeForMask(LaneBitmask LM,
-                                                        LiveInterval &LI) {
-  for (LiveInterval::SubRange &S : LI.subranges())
+LiveInterval::SubRange &getSubRangeForMaskExact(LaneBitmask LM,
+                                                LiveInterval &LI) {
+  return getSubrangeImpl(LM, LI);
+}
+
+const LiveInterval::SubRange &getSubRangeForMaskExact(LaneBitmask LM,
+                                                      const LiveInterval &LI) {
+  return getSubrangeImpl(LM, LI);
+}
+
+/// Find a subrange corresponding to the lane mask @p LM, or a superset of it,
+/// in the live interval @p LI. The interval @p LI is assumed to contain such
+/// a subrange.  This function is used to find corresponding subranges between
+/// the original interval and the new intervals.
+const LiveInterval::SubRange &getSubRangeForMask(LaneBitmask LM,
+                                                 const LiveInterval &LI) {
+  for (const LiveInterval::SubRange &S : LI.subranges())
     if ((S.LaneMask & LM) == LM)
       return S;
   llvm_unreachable("SubRange for this mask not found");
@@ -566,10 +583,8 @@ SlotIndex SplitEditor::buildCopy(Register FromReg, Register ToReg,
   return Def;
 }
 
-VNInfo *SplitEditor::defFromParent(unsigned RegIdx,
-                                   VNInfo *ParentVNI,
-                                   SlotIndex UseIdx,
-                                   MachineBasicBlock &MBB,
+VNInfo *SplitEditor::defFromParent(unsigned RegIdx, const VNInfo *ParentVNI,
+                                   SlotIndex UseIdx, MachineBasicBlock &MBB,
                                    MachineBasicBlock::iterator I) {
   SlotIndex Def;
   LiveInterval *LI = &LIS.getInterval(Edit->get(RegIdx));
@@ -937,7 +952,7 @@ SplitEditor::findShallowDominator(MachineBasicBlock *MBB,
 void SplitEditor::computeRedundantBackCopies(
     DenseSet<unsigned> &NotToHoistSet, SmallVectorImpl<VNInfo *> &BackCopies) {
   LiveInterval *LI = &LIS.getInterval(Edit->get(0));
-  LiveInterval *Parent = &Edit->getParent();
+  const LiveInterval *Parent = &Edit->getParent();
   SmallVector<SmallPtrSet<VNInfo *, 8>, 8> EqualVNs(Parent->getNumValNums());
   SmallPtrSet<VNInfo *, 8> DominatedVNIs;
 
@@ -952,7 +967,7 @@ void SplitEditor::computeRedundantBackCopies(
   // For VNI aggregation of each ParentVNI, collect dominated, i.e.,
   // redundant VNIs to BackCopies.
   for (unsigned i = 0, e = Parent->getNumValNums(); i != e; ++i) {
-    VNInfo *ParentVNI = Parent->getValNumInfo(i);
+    const VNInfo *ParentVNI = Parent->getValNumInfo(i);
     if (!NotToHoistSet.count(ParentVNI->id))
       continue;
     SmallPtrSetIterator<VNInfo *> It1 = EqualVNs[ParentVNI->id].begin();
@@ -990,7 +1005,7 @@ void SplitEditor::computeRedundantBackCopies(
 void SplitEditor::hoistCopies() {
   // Get the complement interval, always RegIdx 0.
   LiveInterval *LI = &LIS.getInterval(Edit->get(0));
-  LiveInterval *Parent = &Edit->getParent();
+  const LiveInterval *Parent = &Edit->getParent();
 
   // Track the nearest common dominator for all back-copies for each ParentVNI,
   // indexed by ParentVNI->id.
@@ -1067,7 +1082,7 @@ void SplitEditor::hoistCopies() {
     if (!Dom.first || Dom.second.isValid())
       continue;
     // This value needs a hoisted copy inserted at the end of Dom.first.
-    VNInfo *ParentVNI = Parent->getValNumInfo(i);
+    const VNInfo *ParentVNI = Parent->getValNumInfo(i);
     MachineBasicBlock *DefMBB = LIS.getMBBFromIndex(ParentVNI->def);
     // Get a less loopy dominator than Dom.first.
     Dom.first = findShallowDominator(Dom.first, DefMBB);
@@ -1237,11 +1252,11 @@ void SplitEditor::extendPHIRange(MachineBasicBlock &B, LiveIntervalCalc &LIC,
     SlotIndex LastUse = End.getPrevSlot();
     // The predecessor may not have a live-out value. That is OK, like an
     // undef PHI operand.
-    LiveInterval &PLI = Edit->getParent();
+    const LiveInterval &PLI = Edit->getParent();
     // Need the cast because the inputs to ?: would otherwise be deemed
     // "incompatible": SubRange vs LiveInterval.
-    LiveRange &PSR = !LM.all() ? getSubRangeForMaskExact(LM, PLI)
-                               : static_cast<LiveRange &>(PLI);
+    const LiveRange &PSR = !LM.all() ? getSubRangeForMaskExact(LM, PLI)
+                                     : static_cast<const LiveRange &>(PLI);
     if (PSR.liveAt(LastUse))
       LIC.extend(LR, End, /*PhysReg=*/0, Undefs);
   }
@@ -1254,7 +1269,7 @@ void SplitEditor::extendPHIKillRanges() {
   // remove it. Otherwise, extend the live interval to reach the end indexes
   // of all predecessor blocks.
 
-  LiveInterval &ParentLI = Edit->getParent();
+  const LiveInterval &ParentLI = Edit->getParent();
   for (const VNInfo *V : ParentLI.valnos) {
     if (V->isUnused() || !V->isPHIDef())
       continue;
@@ -1270,7 +1285,7 @@ void SplitEditor::extendPHIKillRanges() {
   SmallVector<SlotIndex, 4> Undefs;
   LiveIntervalCalc SubLIC;
 
-  for (LiveInterval::SubRange &PS : ParentLI.subranges()) {
+  for (const LiveInterval::SubRange &PS : ParentLI.subranges()) {
     for (const VNInfo *V : PS.valnos) {
       if (V->isUnused() || !V->isPHIDef())
         continue;