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[Docs] More MemorySSA doc updates!

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Thanks again to Michael Kuperstein for the feedback.

llvm-svn: 279032
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George Burgess IV 2016-08-18 02:56:05 +00:00
parent 55e3136679
commit 21ab1f4274
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docs/MemorySSA.rst
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@ -53,16 +53,16 @@ concrete operation. As such, ``BasicBlock``\ s are mapped to ``MemoryPhi``\ s
inside ``MemorySSA``, whereas ``Instruction``\ s are mapped to ``MemoryUse``\ s
and ``MemoryDef``\ s.
Note also that in SSA, Phi nodes merge must-reach definitions (that
is, definite new versions of variables). In MemorySSA, PHI nodes merge
may-reach definitions (that is, until disambiguated, the versions that
reach a phi node may or may not clobber a given variable)
Note also that in SSA, Phi nodes merge must-reach definitions (that is,
definitions that *must* be new versions of variables). In MemorySSA, PHI nodes
merge may-reach definitions (that is, until disambiguated, the versions that
reach a phi node may or may not clobber a given variable).
``MemoryUse``\ s are operations which use but don't modify memory. An example of
a ``MemoryUse`` is a ``load``, or a ``readonly`` function call.
``MemoryDef``\ s are operations which may either modify memory, or which
otherwise clobber memory in unquantifiable ways. Examples of ``MemoryDef``\ s
introduce some kind of ordering constraints. Examples of ``MemoryDef``\ s
include ``store``\ s, function calls, ``load``\ s with ``acquire`` (or higher)
ordering, volatile operations, memory fences, etc.