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//===-- RegAllocBase.h - basic regalloc interface and driver --*- C++ -*---===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines the RegAllocBase class, which is the skeleton of a basic
// register allocation algorithm and interface for extending it. It provides the
// building blocks on which to construct other experimental allocators and test
// the validity of two principles:
//
// - If virtual and physical register liveness is modeled using intervals, then
// on-the-fly interference checking is cheap. Furthermore, interferences can be
// lazily cached and reused.
//
// - Register allocation complexity, and generated code performance is
// determined by the effectiveness of live range splitting rather than optimal
// coloring.
//
// Following the first principle, interfering checking revolves around the
// LiveIntervalUnion data structure.
//
// To fulfill the second principle, the basic allocator provides a driver for
// incremental splitting. It essentially punts on the problem of register
// coloring, instead driving the assignment of virtual to physical registers by
// the cost of splitting. The basic allocator allows for heuristic reassignment
// of registers, if a more sophisticated allocator chooses to do that.
//
// This framework provides a way to engineer the compile time vs. code
// quality trade-off without relying on a particular theoretical solver.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_CODEGEN_REGALLOCBASE
#define LLVM_CODEGEN_REGALLOCBASE
#include "llvm/ADT/OwningPtr.h"
#include "LiveIntervalUnion.h"
#include "RegisterClassInfo.h"
namespace llvm {
template<typename T> class SmallVectorImpl;
class TargetRegisterInfo;
class VirtRegMap;
class LiveIntervals;
class Spiller;
// Forward declare a priority queue of live virtual registers. If an
// implementation needs to prioritize by anything other than spill weight, then
// this will become an abstract base class with virtual calls to push/get.
class LiveVirtRegQueue;
/// RegAllocBase provides the register allocation driver and interface that can
/// be extended to add interesting heuristics.
///
/// Register allocators must override the selectOrSplit() method to implement
/// live range splitting. They must also override enqueue/dequeue to provide an
/// assignment order.
class RegAllocBase {
LiveIntervalUnion::Allocator UnionAllocator;
// Cache tag for PhysReg2LiveUnion entries. Increment whenever virtual
// registers may have changed.
unsigned UserTag;
protected:
// Array of LiveIntervalUnions indexed by physical register.
class LiveUnionArray {
unsigned NumRegs;
LiveIntervalUnion *Array;
public:
LiveUnionArray(): NumRegs(0), Array(0) {}
~LiveUnionArray() { clear(); }
unsigned numRegs() const { return NumRegs; }
void init(LiveIntervalUnion::Allocator &, unsigned NRegs);
void clear();
LiveIntervalUnion& operator[](unsigned PhysReg) {
assert(PhysReg < NumRegs && "physReg out of bounds");
return Array[PhysReg];
}
};
const TargetRegisterInfo *TRI;
MachineRegisterInfo *MRI;
VirtRegMap *VRM;
LiveIntervals *LIS;
RegisterClassInfo RegClassInfo;
LiveUnionArray PhysReg2LiveUnion;
// Current queries, one per physreg. They must be reinitialized each time we
// query on a new live virtual register.
OwningArrayPtr<LiveIntervalUnion::Query> Queries;
RegAllocBase(): UserTag(0), TRI(0), MRI(0), VRM(0), LIS(0) {}
virtual ~RegAllocBase() {}
// A RegAlloc pass should call this before allocatePhysRegs.
void init(VirtRegMap &vrm, LiveIntervals &lis);
// Get an initialized query to check interferences between lvr and preg. Note
// that Query::init must be called at least once for each physical register
// before querying a new live virtual register. This ties Queries and
// PhysReg2LiveUnion together.
LiveIntervalUnion::Query &query(LiveInterval &VirtReg, unsigned PhysReg) {
Queries[PhysReg].init(UserTag, &VirtReg, &PhysReg2LiveUnion[PhysReg]);
return Queries[PhysReg];
}
// Invalidate all cached information about virtual registers - live ranges may
// have changed.
void invalidateVirtRegs() { ++UserTag; }
// The top-level driver. The output is a VirtRegMap that us updated with
// physical register assignments.
//
// If an implementation wants to override the LiveInterval comparator, we
// should modify this interface to allow passing in an instance derived from
// LiveVirtRegQueue.
void allocatePhysRegs();
// Get a temporary reference to a Spiller instance.
virtual Spiller &spiller() = 0;
/// enqueue - Add VirtReg to the priority queue of unassigned registers.
virtual void enqueue(LiveInterval *LI) = 0;
/// dequeue - Return the next unassigned register, or NULL.
virtual LiveInterval *dequeue() = 0;
// A RegAlloc pass should override this to provide the allocation heuristics.
// Each call must guarantee forward progess by returning an available PhysReg
// or new set of split live virtual registers. It is up to the splitter to
// converge quickly toward fully spilled live ranges.
virtual unsigned selectOrSplit(LiveInterval &VirtReg,
SmallVectorImpl<LiveInterval*> &splitLVRs) = 0;
// A RegAlloc pass should call this when PassManager releases its memory.
virtual void releaseMemory();
// Helper for checking interference between a live virtual register and a
// physical register, including all its register aliases. If an interference
// exists, return the interfering register, which may be preg or an alias.
unsigned checkPhysRegInterference(LiveInterval& VirtReg, unsigned PhysReg);
/// assign - Assign VirtReg to PhysReg.
/// This should not be called from selectOrSplit for the current register.
void assign(LiveInterval &VirtReg, unsigned PhysReg);
/// unassign - Undo a previous assignment of VirtReg to PhysReg.
/// This can be invoked from selectOrSplit, but be careful to guarantee that
/// allocation is making progress.
void unassign(LiveInterval &VirtReg, unsigned PhysReg);
// Helper for spilling all live virtual registers currently unified under preg
// that interfere with the most recently queried lvr. Return true if spilling
// was successful, and append any new spilled/split intervals to splitLVRs.
bool spillInterferences(LiveInterval &VirtReg, unsigned PhysReg,
SmallVectorImpl<LiveInterval*> &SplitVRegs);
/// addMBBLiveIns - Add physreg liveins to basic blocks.
void addMBBLiveIns(MachineFunction *);
#ifndef NDEBUG
// Verify each LiveIntervalUnion.
void verify();
#endif
// Use this group name for NamedRegionTimer.
static const char *TimerGroupName;
public:
/// VerifyEnabled - True when -verify-regalloc is given.
static bool VerifyEnabled;
private:
void seedLiveRegs();
void spillReg(LiveInterval &VirtReg, unsigned PhysReg,
SmallVectorImpl<LiveInterval*> &SplitVRegs);
};
} // end namespace llvm
#endif // !defined(LLVM_CODEGEN_REGALLOCBASE)
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