llvm-svn: 126003

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

Loop splitting is better handled by the more generic global region splitting
based on the edge bundle graph.

llvm-svn: 125243

This fixes a bug where splitSingleBlocks() could split a live range after a
terminator instruction.

llvm-svn: 125237

No functional changes intended.

llvm-svn: 125231

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

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

No functional change.

llvm-svn: 124257

llvm-svn: 123925

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

The analysis will be needed by both the greedy register allocator and the
X86FloatingPoint pass. It only needs to be computed once when the CFG doesn't
change.

This pass is very fast, usually showing up as 0.0% wall time.

llvm-svn: 122832

Edge bundles is an annotation on the CFG that turns it into a bipartite directed
graph where each basic block is connected to an outgoing and an ingoing bundle.
These bundles are useful for identifying regions of the CFG for live range
splitting.

llvm-svn: 122301

Bypass loops have the current live range live through, but contain no uses or
defs. Splitting around a bypass loop can free registers for other uses inside
the loop by spilling the split range.

llvm-svn: 121871

This method returns the set of loops with uses that are candidates for
splitting.

llvm-svn: 121870

Whenever splitting wants to insert a copy, it checks if the value can be
rematerialized cheaply instead.

Missing features:
- Delete instructions when all uses have been rematerialized.
- Truncate live ranges to the remaining uses after rematerialization.

llvm-svn: 118702

source, and let rewrite() clean it up.

This way, kill flags on the inserted copies are fixed as well during rewrite().

We can't just assume that all the copies we insert are going to be kills since
critical edges into loop headers sometimes require both source and dest to be
live out of a block.

llvm-svn: 117980

in SSAUpdaterImpl.h

Verifying live intervals revealed that the old method was completely wrong, and
we need an iterative approach to calculating PHI placemant. Fortunately, we have
MachineDominators available, so we don't have to compute that over and over
like SSAUpdaterImpl.h must.

Live-out values are cached between calls to mapValue() and computed in a greedy
way, so most calls will be working with very small block sets.

Thanks to Bob for explaining how this should work.

llvm-svn: 117599

proper SSA updating.

This doesn't cause MachineDominators to be recomputed since we are already
requiring MachineLoopInfo which uses dominators as well.

llvm-svn: 117598

live out.

This doesn't prevent us from inserting a loop preheader later on, if that is
better.

llvm-svn: 117424

Critical edges going into a loop are not as bad as critical exits. We can handle
them by splitting the critical edge, or by having both inside and outside
registers live out of the predecessor.

llvm-svn: 117423

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.

llvm-svn: 117174

llvm-svn: 117143

llvm-svn: 116580

llvm-svn: 116547

splitting or spillling, and to help with rematerialization.

Use LiveRangeEdit in InlineSpiller and SplitKit. This will eventually make it
possible to share remat code between InlineSpiller and SplitKit.

llvm-svn: 116543

functions: computeRemainder and rewrite.

When the remainder breaks up into multiple components, remember to rewrite those
uses as well.

llvm-svn: 116121

reusable, but that is no longer relevant since a split will always replace the
original.

llvm-svn: 115709

never kept after splitting.

Keeping the original interval made sense when the split region doesn't modify
the register, and the original is spilled. We can get the same effect by
detecting reloaded values when spilling around copies.

llvm-svn: 115695

Insert copy after defining instruction.

Fix LiveIntervalMap::extendTo to properly handle live segments starting before
the current basic block.

Make sure the open live range is extended to the inserted copy's use slot.

llvm-svn: 115665

creating it before and subtracting split ranges.

This way, the SSA update code in LiveIntervalMap can properly create and use new
phi values in dupli. Now it is possible to create split regions where a value
escapes along two different CFG edges, creating phi values outside the split
region.

This is a work in progress and probably quite broken.

llvm-svn: 114492

great deal because we don't have to worry about maintaining SSA form.

Unconditionally copy back to dupli when the register is live out of the split
range, even if the live-out value was defined outside the range. Skipping the
back-copy only makes sense when the live range is going to spill outside the
split range, and we don't know that it will. Besides, this was a hack to avoid
SSA update issues.

Clear up some confusion about the end point of a half-open LiveRange. Methinks
LiveRanges need to be closed so both start and end are included in the range.
The low bits of a SlotIndex are symbolic, so a half-open range doesn't really
make sense. This would be a pervasive change, though.

llvm-svn: 114043

edited without actually using LiveIntervalMap functionality.

llvm-svn: 113816

llvm-svn: 113815

map discovers the iterated dominance frontier for free.

llvm-svn: 111400

LiveIntervalMap maps values from a parent LiveInterval to a child interval that
is a strict subset. It will create phi-def values as needed to preserve the
VNInfo SSA form in the child interval.

This leads to an algorithm very similar to the one in SSAUpdaterImpl.h, but with
enough differences that the code can't be reused:

- We don't need to manipulate PHI instructions.
- LiveIntervals have kills.
- We have MachineDominatorTree.
- We can use df_iterator.

llvm-svn: 111393

The earliestStart argument is entirely specific to linear scan allocation, and
can be easily calculated by RegAllocLinearScan.

Replace std::vector with SmallVector.

llvm-svn: 111055

When a live range is contained a single block, we can split it around
instruction clusters. The current approach is very primitive, splitting before
and after the largest gap between uses.

llvm-svn: 111043