bunch of associated comments, because it doesn't have anything to do
with DAGs or scheduling. This is another step in decoupling MachineInstr
emitting from scheduling.
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set, these flags indicate the instructions source / def operands have special
register allocation requirement that are not captured in their register classes.
Post-allocation passes (e.g. post-alloc scheduler) should not change their
allocations. e.g. ARM::LDRD require the two definitions to be allocated
even / odd register pair.
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instruction to execute. This can be used for transformations (like two-address
conversion) to remat an instruction instead of generating a "move"
instruction. The idea is to decrease the live ranges and register pressure and
all that jazz.
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x86 backend where instructions were not marked maystore/mayload, and perf issues where
instructions were not marked neverHasSideEffects. It would be really nice if we could
write patterns for copy instructions.
I have audited all the x86 instructions down to MOVDQAmr. The flags on others and on
other targets are probably not right in all cases, but no clients currently use this
info that are enabled by default.
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instruction flag, and use the flag along with a virtual member function
hook for targets to override if there are instructions that are only
trivially rematerializable with specific operands (i.e. constant pool
loads).
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with a general target hook to identify rematerializable instructions. Some
instructions are only rematerializable with specific operands, such as loads
from constant pools, while others are always rematerializable. This hook
allows both to be identified as being rematerializable with the same
mechanism.
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not be used for anything other than backwards compat constraint handling.
Add support for a new DisableEncoding property which contains a list of
registers that should not be encoded by the generated code emitter. Convert
the codeemitter generator to use this, fixing some PPC JIT regressions.
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SNDPOutFlag to DAG nodes. These properties do not belong to target specific
instructions.
* Added DAG node property SNDPOptInFlag. It's same as SNDPInFlag except it's
optional. Used by ret / call, etc.
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Currently tblgen cannot tell which operands in the operand list are results so
it assumes the first one is a result. This is bad. Ideally we would fix this
by separating results from inputs, e.g. (res R32:$dst),
(ops R32:$src1, R32:$src2). But that's a more distruptive change. Adding
'let noResults = 1' is the workaround to tell tblgen that the instruction does
not produces a result. It works for now since tblgen does not support
instructions which produce multiple results.
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* Enhanced tblgen to handle instructions which have chain operand and writes a
chain result.
* Enhanced tblgen to handle instructions which produces no results. Part of
the change is a temporary hack which relies on instruction property (e.g.
isReturn, isBranch). The proper fix would be to change the .td syntax to
separate results dag from ops dag.
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