This field specifies registers that are preserved across function calls,
but that should not be included in the generates SaveList array.
This can be used ot generate regmasks for architectures that save
registers through other means, like SPARC's register windows.
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algorithm when assigning EnumValues to the synthesized registers.
The current algorithm, LessRecord, uses the StringRef compare_numeric
function. This function compares strings, while handling embedded numbers.
For example, the R600 backend registers are sorted as follows:
T1
T1_W
T1_X
T1_XYZW
T1_Y
T1_Z
T2
T2_W
T2_X
T2_XYZW
T2_Y
T2_Z
In this example, the 'scaling factor' is dEnum/dN = 6 because T0, T1, T2
have an EnumValue offset of 6 from one another. However, in other parts
of the register bank, the scaling factors are different:
dEnum/dN = 5:
KC0_128_W
KC0_128_X
KC0_128_XYZW
KC0_128_Y
KC0_128_Z
KC0_129_W
KC0_129_X
KC0_129_XYZW
KC0_129_Y
KC0_129_Z
The diff lists do not work correctly because different kinds of registers have
different 'scaling factors'. This new algorithm, LessRecordRegister, tries to
enforce a scaling factor of 1. For example, the registers are now sorted as
follows:
T1
T2
T3
...
T0_W
T1_W
T2_W
...
T0_X
T1_X
T2_X
...
KC0_128_W
KC0_129_W
KC0_130_W
...
For the Mips and R600 I see a 19% and 6% reduction in size, respectively. I
did see a few small regressions, but the differences were on the order of a
few bytes (e.g., AArch64 was 16 bytes). I suspect there will be even
greater wins for targets with larger register files.
Patch reviewed by Jakob.
rdar://14006013
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NOTE: If this broke your out-of-tree backend, in *RegisterInfo.td, change
the instances of SubRegIndex that have a comps template arg to use the
ComposedSubRegIndex class instead.
In TableGen land, this adds Size and Offset attributes to SubRegIndex,
and the ComposedSubRegIndex class, for which the Size and Offset are
computed by TableGen. This also adds an accessor in MCRegisterInfo, and
Size/Offsets for the X86 and ARM subreg indices.
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The size reduction in the RegDiffLists are rather dramatic. Here are a few
size differences for MCTargetDesc.o files (before and after) in bytes:
R600 - 36160B - 11184B - 69% reduction
ARM - 28480B - 8368B - 71% reduction
Mips - 816B - 576B - 29% reduction
One side effect of dynamically computing the aliases is that the iterator does
not guarantee that the entries are ordered or that duplicates have been removed.
The documentation implies this is a safe assumption and I found no clients that
requires these attributes (i.e., strict ordering and uniqueness).
My local LNT tester results showed no execution-time failures or significant
compile-time regressions (i.e., beyond what I would consider noise) for -O0g,
-O2 and -O3 runs on x86_64 and i386 configurations.
rdar://12906217
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This lane mask provides information about which register lanes
completely cover super-registers. See the block comment before
getCoveringLanes().
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MC disassembler clients (LLDB) are interested in querying if an
instruction may affect control flow other than by virtue of being
an explicit branch instruction. For example, instructions which
write directly to the PC on some architectures.
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This is much simpler to reason about, more efficient, and
fixes some corner cases involving implicit super-register defs.
Fixed rdar://12797931.
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At build-time register pressure was always computed in terms of
register units. But the compile-time API was expressed in terms of
register classes because it was intended for virtual registers (and
physical register units weren't yet used anywhere in codegen).
Now that the codegen uses physreg units consistently, prepare for
tracking register pressure also in terms of live units, not live
registers.
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Explicitly allow composition of null sub-register indices, and handle
that common case in an inlinable stub.
Use a compressed table implementation instead of the previous nested
switches which generated pretty bad code.
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Most places can use PrintFatalError as the unwinding mechanism was not
used for anything other than printing the error. The single exception
was CodeGenDAGPatterns.cpp, where intermediate errors during type
resolution were ignored to simplify incremental platform development.
This use is replaced by an error flag in TreePattern and bailout earlier
in various places if it is set.
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Some of these dyn_cast<>'s would be better phrased as isa<> or cast<>.
That will happen in a future patch.
There are also two dyn_cast_or_null<>'s slipped in instead of
dyn_cast<>'s, since they were causing crashes with just dyn_cast<>.
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Sub-register lane masks are bitmasks that can be used to determine if
two sub-registers of a virtual register will overlap. For example, ARM's
ssub0 and ssub1 sub-register indices don't overlap each other, but both
overlap dsub0 and qsub0.
The lane masks will be accurate on most targets, but on targets that use
sub-register indexes in an irregular way, the masks may conservatively
report that two sub-register indices overlap when the eventually
allocated physregs don't.
Irregular register banks also mean that the bits in a lane mask can't be
mapped onto register units, but the concept is similar.
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Preserve the Composites map in the CodeGenSubRegIndex class so it can be
used to determine which sub-register indices can actually be composed.
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Apparently, NumSubRegIndices was completely unused before. Adjust it by
one to include the null subreg index, just like getNumRegs() includes
the null register.
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TableGen sometimes synthesizes missing sub-register indexes. Emit these
indexes as enumerators in the target namespace along with the
user-defined ones.
Also take this opportunity to stop creating new Record objects for
synthetic indexes.
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These tables were indexed by [register][subreg index] which made them,
very large and sparse.
Replace them with lists of sub-register indexes that match the existing
lists of sub-registers. MCRI::getSubReg() becomes a very short linear
search, like getSubRegIndex() already was.
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The TableGenBackend base class doesn't do much, and will be removed
completely soon.
Patch by Sean Silva!
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Each register unit has one or two root registers. The full set of
registers containing a given register unit can be computed as the union
of the root registers and their super-registers.
Provide an MCRegUnitRootIterator class to enumerate the roots.
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Register units are already used internally in TableGen to compute
register pressure sets and overlapping registers. This patch makes them
available to the code generators.
The register unit lists are differentially encoded so they can be reused
for many related registers. This keeps the total size of the lists below
200 bytes for most targets. ARM has the largest table at 560 bytes.
Add an MCRegUnitIterator for traversing the register unit lists. It
provides an abstract interface so the representation can be changed in
the future without changing all clients.
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TableGen already computes register units as the basic unit of
interference. We can use that to compute the set of overlapping
registers.
This means that we can easily compute overlap sets for one register at a
time. There is no benefit to computing all registers at once.
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Many targets always use the same bitwise encoding value for physical
registers in all (or most) instructions. Add this mapping to the
.td files and TableGen'erate the information and expose an accessor
in MCRegisterInfo.
patch by Tom Stellard.
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This manually enumerated list of super-register classes has been
superceeded by the automatically computed super-register class masks
available through SuperRegClassIterator.
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This is a pointer into one of the tables used by
getMatchingSuperRegClass(). It makes it possible to use a shared
implementation of that function.
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The RC->getSubClassMask() pointer now points to a sequence of register
class bit masks. The first bit mask is the normal sub-class mask. The
following masks are super-reg class masks used by
getMatchingSuperRegClass().
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Many register classes only have a few super-registers, so it is not
necessary to keep individual bit masks for all possible sub-register
indices.
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Some targets have no sub-registers at all. Use the TargetRegisterInfo
versions of composeSubRegIndices(), getSubClassWithSubReg(), and
getMatchingSuperRegClass() for those targets.
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This is a new algorithm that finds sets of register units that can be
used to model registers pressure. This handles arbitrary, overlapping
register classes. Each register class is associated with a (small)
list of pressure sets. These are the dimensions of pressure affected
by the register class's liveness.
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