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Document legacy pass manager extension points 

Differential Revision: https://reviews.llvm.org/D64093

llvm-svn: 365142
This commit is contained in:
Serge Guelton 2019-07-04 14:03:11 +00:00
parent 5f73e37af8
commit 85fc597f26
2 changed files with 27 additions and 3 deletions
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4
llvm/docs/ReleaseNotes.rst
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@ -45,6 +45,10 @@ Non-comprehensive list of changes in this release
the platform's libc) without specifying ``-ffreestanding`` may need to either the platform's libc) without specifying ``-ffreestanding`` may need to either
pass ``-fno-builtin-bcmp``, or provide a ``bcmp`` function. pass ``-fno-builtin-bcmp``, or provide a ``bcmp`` function.
* Two new extension points, namely ``EP_FullLinkTimeOptimizationEarly`` and
``EP_FullLinkTimeOptimizationLast`` are available for plugins to specialize
the legacy pass manager full LTO pipeline.
.. NOTE .. NOTE
If you would like to document a larger change, then you can add a If you would like to document a larger change, then you can add a
subsection about it right here. You can copy the following boilerplate subsection about it right here. You can copy the following boilerplate

20
llvm/docs/WritingAnLLVMPass.rst
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@ -178,6 +178,18 @@ without modifying it then the third argument is set to ``true``; if a pass is
an analysis pass, for example dominator tree pass, then ``true`` is supplied as an analysis pass, for example dominator tree pass, then ``true`` is supplied as
the fourth argument. the fourth argument.
If we want to register the pass as a step of an existing pipeline, some extension
points are provided, e.g. ``PassManagerBuilder::EP_EarlyAsPossible`` to apply our
pass before any optimization, or ``PassManagerBuilder::EP_FullLinkTimeOptimizationLast``
to apply it after Link Time Optimizations.
.. code-block:: c++
static llvm::RegisterStandardPasses Y(
llvm::PassManagerBuilder::EP_EarlyAsPossible,
[](const llvm::PassManagerBuilder &Builder,
llvm::legacy::PassManagerBase &PM) { PM.add(new Hello()); });
As a whole, the ``.cpp`` file looks like: As a whole, the ``.cpp`` file looks like:
.. code-block:: c++ .. code-block:: c++
@ -186,6 +198,9 @@ As a whole, the ``.cpp`` file looks like:
#include "llvm/IR/Function.h" #include "llvm/IR/Function.h"
#include "llvm/Support/raw_ostream.h" #include "llvm/Support/raw_ostream.h"
#include "llvm/IR/LegacyPassManager.h"
#include "llvm/Transforms/IPO/PassManagerBuilder.h"
using namespace llvm; using namespace llvm;
namespace { namespace {
@ -206,6 +221,11 @@ As a whole, the ``.cpp`` file looks like:
false /* Only looks at CFG */, false /* Only looks at CFG */,
false /* Analysis Pass */); false /* Analysis Pass */);
static RegisterStandardPasses Y(
PassManagerBuilder::EP_EarlyAsPossible,
[](const PassManagerBuilder &Builder,
legacy::PassManagerBase &PM) { PM.add(new Hello()); });
Now that it's all together, compile the file with a simple "``gmake``" command Now that it's all together, compile the file with a simple "``gmake``" command
from the top level of your build directory and you should get a new file from the top level of your build directory and you should get a new file
"``lib/LLVMHello.so``". Note that everything in this file is "``lib/LLVMHello.so``". Note that everything in this file is