mbenfield created this revision.
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This option is necessary for effective AutoFDO, and it also seems that
the `create_llvm_prof` converter won't work if the binary is compiled
without it.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D101937
Files:
clang/docs/UsersManual.rst
Index: clang/docs/UsersManual.rst
===================================================================
--- clang/docs/UsersManual.rst
+++ clang/docs/UsersManual.rst
@@ -1911,14 +1911,16 @@
usual build cycle when using sample profilers for optimization:
1. Build the code with source line table information. You can use all the
- usual build flags that you always build your application with. The only
- requirement is that you add ``-gline-tables-only`` or ``-g`` to the
- command line. This is important for the profiler to be able to map
- instructions back to source line locations.
+ usual build flags that you always build your application with. There are two
+ flags you must use. The first is ``-gline-tables-only`` or ``-g``. This is
+ important for the profiler to be able to map instructions back to source
line
+ locations. The second is ``-fdebug-info-for-profiling``. This will add
+ discriminators so that different expressions on the same source line can be
+ distinguished, as well as some other changes making profiling more
effective.
.. code-block:: console
- $ clang++ -O2 -gline-tables-only code.cc -o code
+ $ clang++ -O2 -fdebug-info-for-profiling -gline-tables-only code.cc -o
code
2. Run the executable under a sampling profiler. The specific profiler
you use does not really matter, as long as its output can be converted
Index: clang/docs/UsersManual.rst
===================================================================
--- clang/docs/UsersManual.rst
+++ clang/docs/UsersManual.rst
@@ -1911,14 +1911,16 @@
usual build cycle when using sample profilers for optimization:
1. Build the code with source line table information. You can use all the
- usual build flags that you always build your application with. The only
- requirement is that you add ``-gline-tables-only`` or ``-g`` to the
- command line. This is important for the profiler to be able to map
- instructions back to source line locations.
+ usual build flags that you always build your application with. There are two
+ flags you must use. The first is ``-gline-tables-only`` or ``-g``. This is
+ important for the profiler to be able to map instructions back to source line
+ locations. The second is ``-fdebug-info-for-profiling``. This will add
+ discriminators so that different expressions on the same source line can be
+ distinguished, as well as some other changes making profiling more effective.
.. code-block:: console
- $ clang++ -O2 -gline-tables-only code.cc -o code
+ $ clang++ -O2 -fdebug-info-for-profiling -gline-tables-only code.cc -o code
2. Run the executable under a sampling profiler. The specific profiler
you use does not really matter, as long as its output can be converted
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