llvm-svn: 126975

This speeds up the greedy register allocator by 15%.
DenseMap is not as fast as one might hope.

llvm-svn: 126921

llvm-svn: 126912

This is a waste of time since we already know how to evict all interferences
which is a better approach anyway.

llvm-svn: 126798

This effectively disables the 'turbo' functionality of the greedy register
allocator where all new live ranges created by splitting would be reconsidered
as if they were originals.

There are two reasons for doing this, 1. It guarantees that the algorithm
terminates. Early versions were prone to infinite looping in certain corner
cases. 2. It is a 2x speedup. We can skip a lot of unnecessary interference
checks that won't lead to good splitting anyway.

The problem is that region splitting only gets one shot, so it should probably
be changed to target multiple physical registers at once.

Local live range splitting is still 'turbo' enabled. It only accounts for a
small fraction of compile time, so it is probably not necessary to do anything
about that.

llvm-svn: 126781

llvm-svn: 126463

New live ranges are assigned in long -> short order, but live ranges that have
been evicted at least once are deferred and assigned in short -> long order.

Also disable splitting and spilling for live ranges seen for the first time.

The intention is to create a realistic interference pattern from the heavy live
ranges before starting splitting and spilling around it.

llvm-svn: 126451

When a large live range is evicted, it will usually be split when it comes
around again. By deferring evicted live ranges, the splitting happens at a time
when the interference pattern is more realistic. This prevents repeated
splitting and evictions.

llvm-svn: 126282

llvm-svn: 126277

Use interval sizes instead of spill weights to determine if it is legal to evict
interference. A smaller interval can evict interference if all interfering live
ranges are larger.

Allow multiple interferences to be evicted as along as they are all larger than
the live range being allocated.

Spill weights are still used to select the preferred eviction candidate.

llvm-svn: 126276

This is based on the observation that long live ranges are more difficult to
allocate, so there is a better chance of solving the puzzle by handling the big
pieces first. The allocator will evict and split long alive ranges when they get
in the way.

RABasic is still using spill weights for its priority queue, so the interface to
the queue has been virtualized.

llvm-svn: 126259

An original endpoint is an instruction that killed or defined the original live
range before any live ranges were split.

When splitting global live ranges, avoid creating local live ranges without any
original endpoints. We may still create global live ranges without original
endpoints, but such a range won't be split again, and live range splitting still
terminates.

llvm-svn: 126151

llvm-svn: 126005

llvm-svn: 126001

The rewriter works almost identically to -rewriter=trivial, except it also
eliminates any identity copies.

This makes the new register allocators independent of VirtRegRewriter.cpp which
will be going away at the same time as RegAllocLinearScan.

llvm-svn: 125967

llvm-svn: 125789

A local live range is live in a single basic block. If such a range fails to
allocate, try to find a sub-range that would get a larger spill weight than its
interference.

llvm-svn: 125764

llvm-svn: 125238

No functional changes intended.

llvm-svn: 125231

Registers are not allocated strictly in spill weight order when live range
splitting and spilling has created new shorter intervals with higher spill
weights.

When one of the new heavy intervals conflicts with a single lighter interval,
simply evict the old interval instead of trying to split the heavy one.

The lighter interval is a better candidate for splitting, it has a smaller use
density.

llvm-svn: 125151

llvm-svn: 125137

The last split point can be anywhere in the block, so it interferes with the
strictly monotonic requirements of advanceTo().

llvm-svn: 125132

instruction in a basic block.

llvm-svn: 125116

This is a lot easier than trying to get kill flags right during live range
splitting and rematerialization.

llvm-svn: 125113

llvm-svn: 125109

If a live range is used by a terminator instruction, and that live range needs
to leave the block on the stack or in a different register, it can be necessary
to have both sides of the split live at the terminator instruction.

Example:

  %vreg2 = COPY %vreg1
  JMP %vreg1

Becomes after spilling %vreg2:

  SPILL %vreg1
  JMP %vreg1

The spill doesn't kill the register as is normally the case.

llvm-svn: 125102

If the interference overlaps the instruction, we cannot separate it.

llvm-svn: 124918

If these inequalities don't hold, we are creating a live range split that won't
allocate.

llvm-svn: 124917

If interference reaches the last split point, it is effectively live out and
should be marked as 'MustSpill'.

This can make a difference when the terminator uses a register. There is no way
that register can be reused in the outgoing CFG bundle, even if it isn't live
out.

llvm-svn: 124900

We should not be attempting a region split if it won't lead to at least one
directly allocatable interval. That could cause infinite splitting loops.

llvm-svn: 124893

When the live range is live through a block that doesn't use the register, but
that has interference, region splitting wants to split at the top and bottom of
the basic block.

llvm-svn: 124839

llvm-svn: 124815

These end points come from the inserted copies, and can be passed directly to
useIntv. This simplifies the coloring code.

llvm-svn: 124799

llvm-svn: 124779

llvm-svn: 124778

The greedy register allocator revealed some problems with the value mapping in
SplitKit. We would sometimes start mapping values before all defs were known,
and that could change a value from a simple 1-1 mapping to a multi-def mapping
that requires ssa update.

The new approach collects all defs and register assignments first without
filling in any live intervals. Only when finish() is called, do we compute
liveness and mapped values. At this time we know with certainty which values map
to multiple values in a split range.

This also has the advantage that we can compute live ranges based on the
remaining uses after rematerializing at split points.

The current implementation has many opportunities for compile time optimization.

llvm-svn: 124765

The value mapping gets confused about which original values have multiple new
definitions so they may need phi insertions.

This could probably be simplified by letting enterIntvBefore() take a live range
to be added following the instruction. As long as the range stays inside the
same basic block, value mapping shouldn't be a problem.

llvm-svn: 123926

interval after an instruction. The leaveIntvAfter() method only adds liveness
from the instruction's boundary index to the inserted copy.

Ideally, SplitKit should be smarter about this, perhaps by combining useIntv()
and leaveIntvAfter() into one method that guarantees continuity.

llvm-svn: 123858

Region splitting includes loop splitting as a subset, and it is more generic.
The splitting heuristics for variables that are live in more than one block are
now:

1. Try to create a region that covers multiple basic blocks.
2. Try to create a new live range for each block with multiple uses.
3. Spill.

Steps 2 and 3 are similar to what the standard spiller is doing.

llvm-svn: 123853

Analyze the live range's behavior entering and leaving basic blocks. Compute an
interference pattern for each allocation candidate, and use SpillPlacement to
find an optimal region where that register can be live.

This code is still not enabled.

llvm-svn: 123774