[docs] Graduate VectorizationPlan.rst from proposal.

[fhahn]

Summary

VPlan has become an integral part of the inner loop vectorizer pipeline
that has been actively developed over the previous years. Let's move
VectorizationPlan.rst from the proposal stage to bring the docs in line
and to avoid confusion when reading the docs.

[rengolin]

Well past the time! :D

llvm/docs/GettingInvolved.rst

 
 .. toctree::
    :hidden:
 
    Proposals/GitHubMove
    BugpointRedesign
    Proposals/TestSuite
    Proposals/VariableNames
-   Proposals/VectorizationPlan
    Proposals/VectorPredication
 
 :doc:`Proposals/GitHubMove`
    Proposal to move from SVN/Git to GitHub.
 
 :doc:`BugpointRedesign`
    Design doc for a redesign of the Bugpoint tool.
 
 :doc:`Proposals/TestSuite`
    Proposals for additional benchmarks/programs for llvm's test-suite.
 
 :doc:`Proposals/VariableNames`
    Proposal to change the variable names coding standard.
 
-:doc:`Proposals/VectorizationPlan`
-   Proposal to model the process and upgrade the infrastructure of LLVM's Loop Vectorizer.
-
 :doc:`Proposals/VectorPredication`
    Proposal for predicated vector instructions in LLVM.
 
 .. _llvm-community-calendar:
 
 LLVM community calendar
 -----------------------
 

llvm/docs/Vectorizers.rst

 .. image:: linpack-pc.png
 
 Ongoing Development Directions
 ------------------------------
 
 .. toctree::
    :hidden:
 
-   Proposals/VectorizationPlan
+   VectorizationPlan
 
-:doc:`Proposals/VectorizationPlan`
+:doc:`VectorizationPlan`
    Modeling the process and upgrading the infrastructure of LLVM's Loop Vectorizer.
 
 .. _slp-vectorizer:
 
 The SLP Vectorizer
 ==================
 
 Details

llvm/include/llvm/Transforms/Vectorize/LoopVectorize.h

 // 3. InnerLoopVectorizer - A unit that performs the actual
 //    widening of instructions.
 // 4. LoopVectorizationCostModel - A unit that checks for the profitability
 //    of vectorization. It decides on the optimal vector width, which
 //    can be one, if vectorization is not profitable.
 //
 // There is a development effort going on to migrate loop vectorizer to the
 // VPlan infrastructure and to introduce outer loop vectorization support (see
-// docs/Proposal/VectorizationPlan.rst and
+// docs/VectorizationPlan.rst and
 // http://lists.llvm.org/pipermail/llvm-dev/2017-December/119523.html). For this
 // purpose, we temporarily introduced the VPlan-native vectorization path: an
 // alternative vectorization path that is natively implemented on top of the
 // VPlan infrastructure. See EnableVPlanNativePath for enabling.
 //
 //===----------------------------------------------------------------------===//
 //
 // The reduction-variable vectorization is based on the paper:

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

 // 3. InnerLoopVectorizer - A unit that performs the actual
 //    widening of instructions.
 // 4. LoopVectorizationCostModel - A unit that checks for the profitability
 //    of vectorization. It decides on the optimal vector width, which
 //    can be one, if vectorization is not profitable.
 //
 // There is a development effort going on to migrate loop vectorizer to the
 // VPlan infrastructure and to introduce outer loop vectorization support (see
-// docs/Proposal/VectorizationPlan.rst and
+// docs/VectorizationPlan.rst and
 // http://lists.llvm.org/pipermail/llvm-dev/2017-December/119523.html). For this
 // purpose, we temporarily introduced the VPlan-native vectorization path: an
 // alternative vectorization path that is natively implemented on top of the
 // VPlan infrastructure. See EnableVPlanNativePath for enabling.
 //
 //===----------------------------------------------------------------------===//
 //
 // The reduction-variable vectorization is based on the paper: