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[llvm-mca][docs] Move the code marker text into its own subsection. NFC. 

Also fixed a few undecorated 'llvm-mca' references to be highlighted
with the 'program' emphasis.

llvm-svn: 338900
This commit is contained in:
Matt Davis 2018-08-03 15:56:07 +00:00
parent 91f578467c
commit b4588e594f
1 changed files with 39 additions and 36 deletions
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75
llvm/docs/CommandGuide/llvm-mca.rst
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@ -21,43 +21,12 @@ The main goal of this tool is not just to predict the performance of the code
when run on the target, but also help with diagnosing potential performance
issues.
Given an assembly code sequence, llvm-mca estimates the Instructions Per Cycle
(IPC), as well as hardware resource pressure. The analysis and reporting style
were inspired by the IACA tool from Intel.
Given an assembly code sequence, :program:`llvm-mca` estimates the Instructions
Per Cycle (IPC), as well as hardware resource pressure. The analysis and
reporting style were inspired by the IACA tool from Intel.
:program:`llvm-mca` allows the usage of special code comments to mark regions of
the assembly code to be analyzed. A comment starting with substring
``LLVM-MCA-BEGIN`` marks the beginning of a code region. A comment starting with
substring ``LLVM-MCA-END`` marks the end of a code region. For example:
.. code-block:: none
# LLVM-MCA-BEGIN My Code Region
...
# LLVM-MCA-END
Multiple regions can be specified provided that they do not overlap. A code
region can have an optional description. If no user-defined region is specified,
then :program:`llvm-mca` assumes a default region which contains every
instruction in the input file. Every region is analyzed in isolation, and the
final performance report is the union of all the reports generated for every
code region.
Inline assembly directives may be used from source code to annotate the
assembly text:
.. code-block:: c++
int foo(int a, int b) {
__asm volatile("# LLVM-MCA-BEGIN foo");
a += 42;
__asm volatile("# LLVM-MCA-END");
a *= b;
return a;
}
So for example, you can compile code with clang, output assembly, and pipe it
directly into llvm-mca for analysis:
For example, you can compile code with clang, output assembly, and pipe it
directly into :program:`llvm-mca` for analysis:
.. code-block:: bash
@ -207,6 +176,40 @@ EXIT STATUS
:program:`llvm-mca` returns 0 on success. Otherwise, an error message is printed
to standard error, and the tool returns 1.
USING MARKERS TO ANALYZE SPECIFIC CODE BLOCKS
---------------------------------------------
:program:`llvm-mca` allows for the optional usage of special code comments to
mark regions of the assembly code to be analyzed. A comment starting with
substring ``LLVM-MCA-BEGIN`` marks the beginning of a code region. A comment
starting with substring ``LLVM-MCA-END`` marks the end of a code region. For
example:
.. code-block:: none
# LLVM-MCA-BEGIN My Code Region
...
# LLVM-MCA-END
Multiple regions can be specified provided that they do not overlap. A code
region can have an optional description. If no user-defined region is specified,
then :program:`llvm-mca` assumes a default region which contains every
instruction in the input file. Every region is analyzed in isolation, and the
final performance report is the union of all the reports generated for every
code region.
Inline assembly directives may be used from source code to annotate the
assembly text:
.. code-block:: c++
int foo(int a, int b) {
__asm volatile("# LLVM-MCA-BEGIN foo");
a += 42;
__asm volatile("# LLVM-MCA-END");
a *= b;
return a;
}
HOW LLVM-MCA WORKS
------------------