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[docs][NewPM] Add some instructions on how to invoke opt

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Also add link to blog post.

Reviewed By: nickdesaulniers

Differential Revision: https://reviews.llvm.org/D104812
This commit is contained in:
Arthur Eubanks 2021-06-23 13:16:04 -07:00
parent 1f2c61f362
commit 65bbec78f6
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docs/NewPassManager.rst
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@ -5,6 +5,12 @@ Using the New Pass Manager
.. contents::
:local:
Overview
========
For an overview of the new pass manager, see the `blog post
<https://blog.llvm.org/posts/2021-03-26-the-new-pass-manager/>`_.
Adding Passes to a Pass Manager
===============================
@ -350,6 +356,89 @@ invalidated so this is not so much of a concern. See
``OuterAnalysisManagerProxy::Result::registerOuterAnalysisInvalidation()``
for more details.
Invoking ``opt``
================
To use the legacy pass manager:
.. code-block:: shell
$ opt -enable-new-pm=0 -pass1 -pass2 /tmp/a.ll -S
This will be removed once the legacy pass manager is deprecated and removed for
the optimization pipeline.
To use the new PM:
.. code-block:: shell
$ opt -passes='pass1,pass2' /tmp/a.ll -S
The new PM typically requires explicit pass nesting. For example, to run a
function pass, then a module pass, we need to wrap the function pass in a module
adaptor:
.. code-block:: shell
$ opt -passes='function(no-op-function),no-op-module' /tmp/a.ll -S
A more complete example, and ``-debug-pass-manager`` to show the execution
order:
.. code-block:: shell
$ opt -passes='no-op-module,cgscc(no-op-cgscc,function(no-op-function,loop(no-op-loop))),function(no-op-function,loop(no-op-loop))' /tmp/a.ll -S -debug-pass-manager
Improper nesting can lead to error messages such as
.. code-block:: shell
$ opt -passes='no-op-function,no-op-module' /tmp/a.ll -S
opt: unknown function pass 'no-op-module'
The nesting is: module (-> cgscc) -> function -> loop, where the CGSCC nesting is optional.
There are a couple of special cases for easier typing:
* If the first pass is not a module pass, a pass manager of the first pass is
implicitly created
* For example, the following are equivalent
.. code-block:: shell
$ opt -passes='no-op-function,no-op-function' /tmp/a.ll -S
$ opt -passes='function(no-op-function,no-op-function)' /tmp/a.ll -S
* If there is an adaptor for a pass that lets it fit in the previous pass
manager, that is implicitly created
* For example, the following are equivalent
.. code-block:: shell
$ opt -passes='no-op-function,no-op-loop' /tmp/a.ll -S
$ opt -passes='no-op-function,loop(no-op-loop)' /tmp/a.ll -S
For a list of available passes and analyses, including the IR unit (module,
CGSCC, function, loop) they operate on, run
.. code-block:: shell
$ opt --print-passes
or take a look at ``PassRegistry.def``.
To make sure an analysis named ``foo`` is available before a pass, add
``require<foo>`` to the pass pipeline. This adds a pass that simply requests
that the analysis is run. This pass is also subject to proper nesting. For
example, to make sure some function analysis is already computed for all
functions before a module pass:
.. code-block:: shell
$ opt -passes='function(require<my-function-analysis>),my-module-pass' /tmp/a.ll -S
Status of the New and Legacy Pass Managers
==========================================