This is a prototype of an experimental register allocation
framework. It's purpose is not to improve register allocation per se,
but to make it easier to develop powerful live range splitting. I call
it the basic allocator because it is as simple as a global allocator
can be but provides the building blocks for sophisticated register
allocation with live range splitting.
A minimal implementation is provided that trivially spills whenever it
runs out of registers. I'm checking in now to get high-level design
and style feedback. I've only done minimal testing. The next step is
implementing a "greedy" allocation algorithm that does some register
reassignment and makes better splitting decisions.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@117174 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/LiveIntervalUnion.h b/lib/CodeGen/LiveIntervalUnion.h
new file mode 100644
index 0000000..3953c59
--- /dev/null
+++ b/lib/CodeGen/LiveIntervalUnion.h
@@ -0,0 +1,193 @@
+//===-- LiveIntervalUnion.h - Live interval union data struct --*- C++ -*--===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// LiveIntervalUnion is a union of live segments across multiple live virtual
+// registers. This may be used during coalescing to represent a congruence
+// class, or during register allocation to model liveness of a physical
+// register.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CODEGEN_LIVEINTERVALUNION
+#define LLVM_CODEGEN_LIVEINTERVALUNION
+
+#include "llvm/CodeGen/LiveInterval.h"
+#include <vector>
+#include <set>
+
+namespace llvm {
+
+// A LiveSegment is a copy of a LiveRange object used within
+// LiveIntervalUnion. LiveSegment additionally contains a pointer to its
+// original live virtual register (LiveInterval). This allows quick lookup of
+// the live virtual register as we iterate over live segments in a union. Note
+// that LiveRange is misnamed and actually represents only a single contiguous
+// interval within a virtual register's liveness. To limit confusion, in this
+// file we refer it as a live segment.
+struct LiveSegment {
+ SlotIndex start;
+ SlotIndex end;
+ LiveInterval *liveVirtReg;
+
+ LiveSegment(SlotIndex s, SlotIndex e, LiveInterval &lvr)
+ : start(s), end(e), liveVirtReg(&lvr) {}
+
+ bool operator==(const LiveSegment &ls) const {
+ return start == ls.start && end == ls.end && liveVirtReg == ls.liveVirtReg;
+ }
+
+ bool operator!=(const LiveSegment &ls) const {
+ return !operator==(ls);
+ }
+
+ bool operator<(const LiveSegment &ls) const {
+ return start < ls.start || (start == ls.start && end < ls.end);
+ }
+};
+
+/// Compare a live virtual register segment to a LiveIntervalUnion segment.
+inline bool overlap(const LiveRange &lvrSeg, const LiveSegment &liuSeg) {
+ return lvrSeg.start < liuSeg.end && liuSeg.start < lvrSeg.end;
+}
+
+inline bool operator<(SlotIndex V, const LiveSegment &ls) {
+ return V < ls.start;
+}
+
+inline bool operator<(const LiveSegment &ls, SlotIndex V) {
+ return ls.start < V;
+}
+
+/// Union of live intervals that are strong candidates for coalescing into a
+/// single register (either physical or virtual depending on the context). We
+/// expect the constituent live intervals to be disjoint, although we may
+/// eventually make exceptions to handle value-based interference.
+class LiveIntervalUnion {
+ // A set of live virtual register segments that supports fast insertion,
+ // intersection, and removal.
+ //
+ // FIXME: std::set is a placeholder until we decide how to
+ // efficiently represent it. Probably need to roll our own B-tree.
+ typedef std::set<LiveSegment> LiveSegments;
+
+ // A set of live virtual registers. Elements have type LiveInterval, where
+ // each element represents the liveness of a single live virtual register.
+ // This is traditionally known as a live range, but we refer is as a live
+ // virtual register to avoid confusing it with the misnamed LiveRange
+ // class.
+ typedef std::vector<LiveInterval*> LiveVirtRegs;
+
+public:
+ // SegmentIter can advance to the next segment ordered by starting position
+ // which may belong to a different live virtual register. We also must be able
+ // to reach the current segment's containing virtual register.
+ typedef LiveSegments::iterator SegmentIter;
+
+ class InterferenceResult;
+ class Query;
+
+private:
+ unsigned repReg_; // representative register number
+ LiveSegments segments_; // union of virtual reg segements
+ LiveVirtRegs lvrs_; // set of live virtual regs in the union
+
+public:
+ // default ctor avoids placement new
+ LiveIntervalUnion() : repReg_(0) {}
+
+ void init(unsigned repReg) { repReg_ = repReg; }
+
+ SegmentIter begin() { return segments_.begin(); }
+ SegmentIter end() { return segments_.end(); }
+
+ /// FIXME: !!!!!!!!!!! Keeps a non-const ref
+ void unify(LiveInterval &lvr);
+
+ // FIXME: needed by RegAllocGreedy
+ //void extract(const LiveInterval &li);
+
+ /// Cache a single interference test result in the form of two intersecting
+ /// segments. This allows efficiently iterating over the interferences. The
+ /// iteration logic is handled by LiveIntervalUnion::Query which may
+ /// filter interferences depending on the type of query.
+ class InterferenceResult {
+ friend class Query;
+
+ LiveInterval::iterator lvrSegI_; // current position in _lvr
+ SegmentIter liuSegI_; // current position in _liu
+
+ // Internal ctor.
+ InterferenceResult(LiveInterval::iterator lvrSegI, SegmentIter liuSegI)
+ : lvrSegI_(lvrSegI), liuSegI_(liuSegI) {}
+
+ public:
+ // Public default ctor.
+ InterferenceResult(): lvrSegI_(), liuSegI_() {}
+
+ // Note: this interface provides raw access to the iterators because the
+ // result has no way to tell if it's valid to dereference them.
+
+ // Access the lvr segment.
+ const LiveInterval::iterator &lvrSegPos() const { return lvrSegI_; }
+
+ // Access the liu segment.
+ const SegmentIter &liuSeg() const { return liuSegI_; }
+
+ bool operator==(const InterferenceResult &ir) const {
+ return lvrSegI_ == ir.lvrSegI_ && liuSegI_ == ir.liuSegI_;
+ }
+ bool operator!=(const InterferenceResult &ir) const {
+ return !operator==(ir);
+ }
+ };
+
+ /// Query interferences between a single live virtual register and a live
+ /// interval union.
+ class Query {
+ LiveIntervalUnion &liu_;
+ LiveInterval &lvr_;
+ InterferenceResult firstInterference_;
+ // TBD: interfering vregs
+
+ public:
+ Query(LiveInterval &lvr, LiveIntervalUnion &liu): liu_(liu), lvr_(lvr) {}
+
+ LiveInterval &lvr() const { return lvr_; }
+
+ bool isInterference(const InterferenceResult &ir) const {
+ if (ir.lvrSegI_ != lvr_.end()) {
+ assert(overlap(*ir.lvrSegI_, *ir.liuSegI_) &&
+ "invalid segment iterators");
+ return true;
+ }
+ return false;
+ }
+
+ // Does this live virtual register interfere with the union.
+ bool checkInterference() { return isInterference(firstInterference()); }
+
+ // First pair of interfering segments, or a noninterfering result.
+ InterferenceResult firstInterference();
+
+ // Treat the result as an iterator and advance to the next interfering pair
+ // of segments. Visiting each unique interfering pairs means that the same
+ // lvr or liu segment may be visited multiple times.
+ bool nextInterference(InterferenceResult &ir) const;
+
+ // TBD: bool collectInterferingVirtRegs(unsigned maxInterference)
+
+ private:
+ // Private interface for queries
+ void findIntersection(InterferenceResult &ir) const;
+ };
+};
+
+} // end namespace llvm
+
+#endif // !defined(LLVM_CODEGEN_LIVEINTERVALUNION)