The <undef> flag says that a MachineOperand doesn't read its register,
or doesn't depend on the previous value of its register.

A full register def never depends on the previous register value.  A
partial register def may depend on the previous value if it is intended
to update part of a register.

For example:

  %vreg10:dsub_0<def,undef> = COPY %vreg1
  %vreg10:dsub_1<def> = COPY %vreg2

The first copy instruction defines the full %vreg10 register with the
bits not covered by dsub_0 defined as <undef>.  It is not considered a
read of %vreg10.

The second copy modifies part of %vreg10 while preserving the rest.  It
has an implicit read of %vreg10.

This patch adds a MachineOperand::readsReg() method to determine if an
operand reads its register.

Previously, this was modelled by adding a full-register <imp-def>
operand to the instruction.  This approach makes it possible to
determine directly from a MachineOperand if it reads its register.  No
scanning of MI operands is required.

llvm-svn: 141124

Blocks with multiple PHI successors only need to go on the worklist
once.  Use a SmallPtrSet to track the live-out blocks that have already
been handled.  This is a lot faster than the two live range check we
would otherwise do.

Also stop recomputing hasPHIKill flags.  Like RenumberValues(), it is
conservatively correct to leave them in, and they are not used for
anything important.

llvm-svn: 139792

Three out of four clients prefer this interface which is consistent with
extendIntervalEndTo() and LiveRangeCalc::extend().

llvm-svn: 139604

range covers the entire block.

The live range can't be terminated at a random instruction.

llvm-svn: 130619

Luis Felipe Strano Moraes!

llvm-svn: 129558

Both coalescing and register allocation already check aliases for interference,
so these extra segments are only slowing us down.

This speeds up both linear scan and the greedy register allocator.

llvm-svn: 129283

PHI values may be deleted, causing the flags to be wrong. This fixes PR9616.

llvm-svn: 129092

When a virtual register has a single value that is defined as a copy of a
reserved register, permit that copy to be joined. These virtual register are
usually copies of the stack pointer:

  %vreg75<def> = COPY %ESP; GR32:%vreg75
  MOV32mr %vreg75, 1, %noreg, 0, %noreg, %vreg74<kill>
  MOV32mi %vreg75, 1, %noreg, 8, %noreg, 0
  MOV32mi %vreg75<kill>, 1, %noreg, 4, %noreg, 0
  CALLpcrel32 ...

Coalescing these virtual registers early decreases register pressure.
Previously, they were coalesced by RALinScan::attemptTrivialCoalescing after
register allocation was completed.

The lower register pressure causes the mcinst-lowering-cmp0.ll test case to fail
because it depends on linear scan spilling a particular register.

I am deleting 2008-08-05-SpillerBug.ll because it is counting the number of
instructions emitted, and its revision history shows the 'correct' count being
edited many times.

llvm-svn: 128845

We don't expect the real "powf()" on some hosts (and powf() would be available on other hosts).
For consistency, std::pow(double,double) may be called instead.
Or, precision issue might attack us, to see unstable regalloc and stack coloring.

llvm-svn: 128629

This is not supposed to happen, but I have seen the x86 rematter getting
confused when rematerializing partial redefs.

llvm-svn: 127857

I have convinced myself that it can only happen when a phi value dies. When it
happens, allocate new virtual registers for the components.

llvm-svn: 127827

llvm-svn: 127771

llvm-svn: 127388

llvm-svn: 127192

In this case, the value need to be available at the load index instead of the
normal use index.

llvm-svn: 127167

We need to wait until we meet a PHIDef in its defining block before resurrecting
PHIKills in the predecessors.

This should unbreak the llvm-gcc-build-x86_64-darwin10-x-mingw32-x-armeabi bot.

llvm-svn: 126905

llvm-svn: 126815

llvm-svn: 126806

llvm-svn: 126805

Simplify the spill weight calculation a bit by bypassing
getApproximateInstructionCount() and using LiveInterval::getSize() directly.
This changes the computed spill weights, but only by a constant factor in each
function. It should not affect how spill weights compare against each other, and
so it shouldn't affect code generation.

llvm-svn: 125530

No functional changes intended.

llvm-svn: 125231

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

llvm-svn: 125113

After uses of a live range are removed, recompute the live range to only cover
the remaining uses. This is necessary after rematerializing the value before
some (but not all) uses.

llvm-svn: 125058

In that case we simply ignore the landing pad and split live ranges before the
first terminator.

llvm-svn: 124907

A live range cannot be split everywhere in a basic block. A split must go before
the first terminator, and if the variable is live into a landing pad, the split
must happen before the call that can throw.

llvm-svn: 124894

These functions not longer assert when passed 0, but simply return false instead.

No functional change intended.

llvm-svn: 123155

Print virtual registers numbered from 0 instead of the arbitrary
FirstVirtualRegister. The first virtual register is printed as %vreg0.
TRI::NoRegister is printed as %noreg.

llvm-svn: 123107

Always spill the full representative register at any point where any subregister
is live.

This fixes PR8620 which caused the old logic to get confused and not spill
anything at all.

The fundamental problem here is that the coalescer is too aggressive about
physical register coalescing. It sometimes makes it impossible to allocate
registers without these emergency spills.

llvm-svn: 119375

The live range of a register defined by an early clobber starts at the use slot,
not the def slot.

Except when it is an early clobber tied to a use operand. Then it starts at the
def slot like a standard def.

llvm-svn: 119305

This reverts r119183 which borke the buildbots.

llvm-svn: 119270

The live range of a register defined by an early clobber starts at the use slot,
not the def slot.

llvm-svn: 119183

benchmarks hitting an assertion.
Adds LiveIntervalUnion::collectInterferingVRegs.
Fixes "late spilling" by checking for any unspillable live vregs among
all physReg aliases.

llvm-svn: 118701

SlotIndexes when available.

llvm-svn: 117392

perform initialization without static constructors AND without explicit initialization
by the client.  For the moment, passes are required to initialize both their
(potential) dependencies and any passes they preserve.  I hope to be able to relax
the latter requirement in the future.

llvm-svn: 116334

This helps hiding the LiveRange class which really should be private.

llvm-svn: 116244

llvm-svn: 115996

Removed VNInfo::isDefAccurate(). Def "accuracy" can be checked by testing whether LiveIntervals::getInstructionFromIndex(def) returns NULL.

llvm-svn: 114791

llvm-svn: 114779

PHI elimination shouldn't require machineloopinfo since it's used at -O0. Move the requirement to LiveIntervalAnalysis instead. Note this does not change the number of times machineloopinfo is computed.

llvm-svn: 111285

llvm-svn: 110944