Add ADT/IntervalMap.

This is a sorted interval map data structure for small keys and values with
automatic coalescing and bidirectional iteration over coalesced intervals.

Except for coalescing intervals, it provides similar functionality to std::map.
It is however much more compact for small keys and values, and hopefully faster
too.

The container object itself can hold the first few intervals without any
allocations, then it switches to a cache conscious B+-tree representation. A
recycling allocator can be shared between many containers, even between
containers holding different types.

The IntervalMap is initially intended to be used with SlotIndex intervals for:

- Backing store for LiveIntervalUnion that is smaller and faster than std::set.

- Backing store for LiveInterval with less overhead than std::vector for typical
  intervals and O(N log N) merging of large intervals. 99% of virtual registers
  need 4 entries or less and would benefit from the small object optimization.

- Backing store for LiveDebugVariable which doesn't exist yet, but will track
  debug variables during register allocation.

This is a work in progress. Missing items are:

- Performance metrics.
- erase().
- insert() shrinkage.
- clear().
- More performance metrics.
- Simplification and detemplatization.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@119772 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 60 insertions, 0 deletions

diff --git a/lib/Support/IntervalMap.cpp b/lib/Support/IntervalMap.cpp
new file mode 100644
index 0000000..9f5c72f
--- /dev/null
+++ b/lib/Support/IntervalMap.cpp
@@ -0,0 +1,60 @@
+//===- lib/Support/IntervalMap.cpp - A sorted interval map ----------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the few non-templated functions in IntervalMap.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/IntervalMap.h"
+
+namespace llvm {
+namespace IntervalMapImpl {
+
+IdxPair distribute(unsigned Nodes, unsigned Elements, unsigned Capacity,
+                   const unsigned *CurSize, unsigned NewSize[],
+                   unsigned Position, bool Grow) {
+  assert(Elements + Grow <= Nodes * Capacity && "Not enough room for elements");
+  assert(Position <= Elements && "Invalid position");
+  if (!Nodes)
+    return IdxPair();
+
+  // Trivial algorithm: left-leaning even distribution.
+  const unsigned PerNode = (Elements + Grow) / Nodes;
+  const unsigned Extra = (Elements + Grow) % Nodes;
+  IdxPair PosPair = IdxPair(Nodes, 0);
+  unsigned Sum = 0;
+  for (unsigned n = 0; n != Nodes; ++n) {
+    Sum += NewSize[n] = PerNode + (n < Extra);
+    if (PosPair.first == Nodes && Sum > Position)
+      PosPair = IdxPair(n, Position - (Sum - NewSize[n]));
+  }
+  assert(Sum == Elements + Grow && "Bad distribution sum");
+
+  // Subtract the Grow element that was added.
+  if (Grow) {
+    assert(PosPair.first < Nodes && "Bad algebra");
+    assert(NewSize[PosPair.first] && "Too few elements to need Grow");
+    --NewSize[PosPair.first];
+  }
+
+#ifndef NDEBUG
+  Sum = 0;
+  for (unsigned n = 0; n != Nodes; ++n) {
+    assert(NewSize[n] <= Capacity && "Overallocated node");
+    Sum += NewSize[n];
+  }
+  assert(Sum == Elements && "Bad distribution sum");
+#endif
+
+  return PosPair;
+}
+
+} // namespace IntervalMapImpl
+} // namespace llvm 
+