Use SpecificBumpPtrAllocator for LiveInterval

I didn't realize we used a singly linked list for storing subranges,
but that seems bad.

I didn't realize we used a singly linked list for storing subranges.
That seems bad and we should probably switch this to an array

Author: arsenm

llvm/include/llvm/CodeGen/LiveIntervals.h

@@ -65,8 +65,12 @@ class LiveIntervals {
   MachineDominatorTree *DomTree = nullptr;
   std::unique_ptr<LiveIntervalCalc> LICalc;
 
+  // Allocator for RegUnitRanges and SubRanges.
   BumpPtrAllocator Allocator;
 
+  // Allocator for VirtRegIntervals
+  SpecificBumpPtrAllocator<LiveInterval> LIAllocator;
+
   /// Special pool allocator for VNInfo's (LiveInterval val#).
   VNInfo::Allocator VNInfoAllocator;
 
@@ -173,7 +177,7 @@ class LiveIntervals {
   /// Interval removal.
   void removeInterval(Register Reg) {
     auto &Interval = VirtRegIntervals[Reg];
-    Allocator.Deallocate(Interval);
+    // FIXME: SpecificBumpPtrAllocator missing deallocate for asan poisoning
     Interval = nullptr;
   }
 

llvm/lib/CodeGen/LiveIntervals.cpp

@@ -142,10 +142,6 @@ bool LiveIntervals::invalidate(
 }
 
 void LiveIntervals::clear() {
-  // Free the live intervals themselves.
-  for (unsigned i = 0, e = VirtRegIntervals.size(); i != e; ++i)
-    Allocator.Deallocate(VirtRegIntervals[Register::index2VirtReg(i)]);
-  VirtRegIntervals.clear();
   RegMaskSlots.clear();
   RegMaskBits.clear();
   RegMaskBlocks.clear();
@@ -154,6 +150,10 @@ void LiveIntervals::clear() {
     Allocator.Deallocate(LR);
   RegUnitRanges.clear();
 
+  // Free the live intervals themselves.
+  LIAllocator.DestroyAll();
+  VirtRegIntervals.clear();
+
   // Release VNInfo memory regions, VNInfo objects don't need to be dtor'd.
   VNInfoAllocator.Reset();
 }
@@ -222,7 +222,7 @@ LLVM_DUMP_METHOD void LiveIntervals::dump() const { print(dbgs()); }
 
 LiveInterval *LiveIntervals::createInterval(Register reg) {
   float Weight = reg.isPhysical() ? huge_valf : 0.0F;
-  return new (Allocator.Allocate<LiveInterval>()) LiveInterval(reg, Weight);
+  return new (LIAllocator.Allocate()) LiveInterval(reg, Weight);
 }
 
 /// Compute the live interval of a virtual register, based on defs and uses.