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Update ReleaseNotes: expand the section on enabling MemorySSA

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llvm-svn: 375045
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Alina Sbirlea 2019-10-16 21:52:09 +00:00
parent 490dcffb69
commit 2ef49693b1
1 changed files with 14 additions and 1 deletions
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docs/ReleaseNotes.rst
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@ -41,7 +41,20 @@ Non-comprehensive list of changes in this release
for adding a new subsection.
* The ISD::FP_ROUND_INREG opcode and related code was removed from SelectionDAG.
* Enabled MemorySSA as a loop dependency.
* Enabled MemorySSA as a loop dependency. Since
`r370957 <https://reviews.llvm.org/rL370957>`_
(`D58311 <https://reviews.llvm.org/D58311>`_ ``[MemorySSA & LoopPassManager]
Enable MemorySSA as loop dependency. Update tests.``), the MemorySSA analysis
is being preserved and used by a series of loop passes. The most significant
use is in LICM, where the instruction hoisting and sinking relies on aliasing
information provided by MemorySSA vs previously creating an AliasSetTracker.
The LICM step of promoting variables to scalars still relies on the creation
of an AliasSetTracker, but its use is reduced to only be enabled for loops
with a small number of overall memory instructions. This choice was motivated
by experimental results showing compile and run time benefits or replacing the
AliasSetTracker usage with MemorySSA without any performance penalties.
The fact that MemorySSA is now preserved by and available in a series of loop
passes, also opens up opportunities for its use in those respective passes.
.. NOTE
If you would like to document a larger change, then you can add a