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

split intervals. THis means the analysis can be used for multiple splits as long
as curli doesn't shrink.

llvm-svn: 110975

Before spilling a live range, we split it into a separate range for each basic
block where it is used. That way we only get one reload per basic block if the
new smaller ranges can allocate to a register.

This type of splitting is already present in the standard spiller.

llvm-svn: 110934

during live range splitting.

llvm-svn: 110686

necessary.

Sometimes, live range splitting doesn't shrink the current interval, but simply
changes some instructions to use a new interval. That makes the original more
suitable for spilling. In this case, we don't need to duplicate the original.

llvm-svn: 110481

We are now at a point where we can split around simple single-entry, single-exit
loops, although still with some bugs.

llvm-svn: 110257

rewrite instructions for live range splitting.

Still work in progress.

llvm-svn: 109469

The spillers can pluck the analyses they need from the pass reference.

Switch some never-null pointers to references.

llvm-svn: 108969

Determine which loop exit blocks need a 'pre-exit' block inserted.
Recognize when this would be impossible.

llvm-svn: 108941

llvm-svn: 108845

This is a work in progress. So far we have some basic loop analysis to help
determine where it is useful to split a live range around a loop.

The actual loop splitting code from Splitter.cpp is also going to move in here.

llvm-svn: 108842