When trying to rematerialize a value before an instruction that has an
early-clobber redefine of the virtual register, make sure to look up the
correct value number.
Early-clobber defs are moved one slot back, so getBaseIndex is needed to
find the used value number.
Bugpoint was unable to reduce the test case for this, see PR10388.
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Spills should be hoisted out of loops, but we don't want to hoist them
to dominating blocks at the same loop depth. That could cause the spills
to be executed more often.
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Try to move spills as early as possible in their basic block. This can
help eliminate interferences by shortening the live range being
spilled.
This fixes PR10221.
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Remat during spilling triggers dead code elimination. If a phi-def
becomes unused, that may also cause live ranges to split into separate
connected components.
This type of splitting is different from normal live range splitting. In
particular, there may not be a common original interval.
When the split range is its own original, make sure that the new
siblings are also their own originals. The range being split cannot be
used as an original since it doesn't cover the new siblings.
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about to be spilled.
This can only happen when two extra snippet registers are included in the spill,
and there is a copy between them. Hoisting the spill creates problems because
the hoist will mark the copy for later dead code elimination, and spilling the
second register will turn the copy into a spill.
<rdar://problem/9420853>
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This could happen when trying to use a value that had been eliminated after dead
code elimination and folding loads.
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The rematerialized instruction may require a more constrained register class
than the register being spilled. In the test case, the spilled register has been
inflated to the DPR register class, but we are rematerializing a load of the
ssub_0 sub-register which only exists for DPR_VFP2 registers.
The register class is reinflated after spilling, so the conservative choice is
only temporary.
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The instruction to be rematerialized may not be the one defining the register
that is being spilled. The traceSiblingValue() function sees through sibling
copies to find the remat candidate.
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The main register class may have been inflated by live range splitting, so that
register class is not necessarily valid for the snippet instructions.
Use the original register class for the stack slot interval.
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Stack slot real estate is virtually free compared to registers, so it is
advantageous to spill earlier even though the same value is now kept in both a
register and a stack slot.
Also eliminate redundant spills by extending the stack slot live range
underneath reloaded registers.
This can trigger a dead code elimination, removing copies and even reloads that
were only feeding spills.
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I have convinced myself that it can only happen when a phi value dies. When it
happens, allocate new virtual registers for the components.
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After live range splitting, an original value may be available in multiple
registers. Tracing back through the registers containing the same value, find
the best place to insert a spill, determine if the value has already been
spilled, or discover a reaching def that may be rematerialized.
This is only the analysis part. The information is not used for anything yet.
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Remove the unused reserved_ bit vector, no functional change intended.
This doesn't break 'svn blame', this file really is all my fault.
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This allows the allocator to free any resources used by the virtual register,
including physical register assignments.
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Live range splitting can create a number of small live ranges containing only a
single real use. Spill these small live ranges along with the large range they
are connected to with copies. This enables memory operand folding and maximizes
the spill to fill distance.
Work in progress with known bugs.
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This will we used for keeping register allocator data structures up to date
while LiveRangeEdit is trimming live intervals.
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physical register numbers.
This makes the hack used in LiveInterval official, and lets LiveInterval be
oblivious of stack slots.
The isPhysicalRegister() and isVirtualRegister() predicates don't know about
this, so when a variable may contain a stack slot, isStackSlot() should always
be tested first.
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use before rematerializing the load.
This allows us to produce:
addps LCPI0_1(%rip), %xmm2
Instead of:
movaps LCPI0_1(%rip), %xmm3
addps %xmm3, %xmm2
Saving a register and an instruction. The standard spiller already knows how to
do this.
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createMachineVerifierPass and MachineFunction::verify.
The banner is printed before the machine code dump, just like the printer pass.
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The spiller should only spill. The register allocator will drive live range
splitting, it has the needed information about register pressure and
interferences.
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live ranges for the spill register are also defined at the use slot instead of
the normal def slot.
This fixes PR8612 for the inline spiller. A use was being allocated to the same
register as a spilled early clobber def.
This problem exists in all the spillers. A fix for the standard spiller is
forthcoming.
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benchmarks hitting an assertion.
Adds LiveIntervalUnion::collectInterferingVRegs.
Fixes "late spilling" by checking for any unspillable live vregs among
all physReg aliases.
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This way, InlineSpiller does the same amount of splitting as the standard
spiller. Splitting should really be guided by the register allocator, and
doesn't belong in the spiller at all.
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proper SSA updating.
This doesn't cause MachineDominators to be recomputed since we are already
requiring MachineLoopInfo which uses dominators as well.
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