[docs][NFC] Add document of llvm-opt-report.

[arakawamasahiro-fj]

Summary

The llvm-opt-report command does not have an online manual, so I have included a manual article.

[arakawamasahiro-fj]

Please review. This is a simple documentation addition.

[arakawamasahiro-fj]

ping
Please review. This is a simple documentation addition.

[madhur13490]

A couple of nits

llvm/docs/CommandGuide/llvm-opt-report.rst

17

need to?

60–62

Are these the only symbols that can be emitted? If not, it is a good idea to list.

[arakawamasahiro-fj]

line 17:
Update to "need to create".

line 60-62:
There is nothing else, so I will keep the current article.

[arakawamasahiro-fj]

@madhur13490 ping

[madhur13490]

LGTM

llvm/docs/CommandGuide/index.rst

.. toctree::
    llvm-dis
    llvm-dwarfdump
    llvm-dwarfutil
    llvm-lib
    llvm-libtool-darwin
    llvm-link
    llvm-lipo
    llvm-mca
+   llvm-opt-report
    llvm-otool
    llvm-profdata
    llvm-readobj
    llvm-stress
    llvm-symbolizer
    opt
 
 GNU binutils replacements

llvm/docs/CommandGuide/llvm-opt-report.rst

+llvm-opt-report - generate optimization report from YAML
+========================================================
+
+.. program:: llvm-opt-report
+
+SYNOPSIS
+--------
+
+:program:`llvm-opt-report` [*options*] [input]
+
+DESCRIPTION
+-----------
+
+:program:`llvm-opt-report` is a tool to generate an optimization report from YAML optimization record files.
+
+You need to create an input YAML optimization record file before running :program:`llvm-opt-report`.
+
+.. code-block:: console
+
+ $ clang -c foo.c -o foo.o -O3 -fsave-optimization-record
+
+Then, you create a report using the :program:`llvm-opt-report` command with the YAML optimization record file :file:`foo.opt.yaml` as input.
+
+.. code-block:: console
+
+ $ llvm-opt-report foo.opt.yaml -o foo.lst
+
+foo.lst is the generated optimization report.
+
+.. code-block::
+
+ < foo.c
+  1          | void bar();
+  2          | void foo() { bar(); }
+  3          |
+  4          | void Test(int *res, int *c, int *d, int *p, int n) {
+  5          |   int i;
+  6          |
+  7          | #pragma clang loop vectorize(assume_safety)
+  8     V4,1 |   for (i = 0; i < 1600; i++) {
+  9          |     res[i] = (p[i] == 0) ? res[i] : res[i] + d[i];
+ 10          |   }
+ 11          |
+ 12  U16     |   for (i = 0; i < 16; i++) {
+ 13          |     res[i] = (p[i] == 0) ? res[i] : res[i] + d[i];
+ 14          |   }
+ 15          |
+ 16 I        |   foo();
+ 17          |
+ 18          |   foo(); bar(); foo();
+    I        |   ^
+    I        |                 ^
+ 19          | }
+ 20          |
+
+Symbols printed on the left side of the program indicate what kind of optimization was performed.
+The meanings of the symbols are as follows:
+
+- I: The function is inlined.
+- U: The loop is unrolled. The following number indicates the unroll factor.
+- V: The loop is vectorized. The following numbers indicate the vector length and the interleave factor.
+
+OPTIONS
+-------
+
+If ``input`` is "``-``" or omitted, :program:`llvm-opt-report` reads from standard
+input. Otherwise, it will read from the specified filename.
+
+If the :option:`-o` option is omitted, then :program:`llvm-opt-report` will send its output
+to standard output.  If the :option:`-o` option specifies "``-``", then the output will also
+be sent to standard output.
+
+
+.. option:: --help
+
+ Display available options.
+
+.. option:: --version
+
+ Display the version of this program.
+
+.. option:: --format=<string>
+
+ The format of the optimization record file.
+ The Argument is one of the following:
+
+ - yaml
+ - yaml-strtab
+ - bitstream
+
+.. option:: --no-demangle
+
+ Do not demangle function names.
+
+.. option:: -o=<string>
+
+ Output file.
+
+.. option:: -r=<string>
+
+ Root for relative input paths.
+
+.. option:: -s
+
+ Do not include vectorization factors, etc.
+
+EXIT STATUS
+-----------
+
+:program:`llvm-opt-report` returns 0 on success. Otherwise, an error message is printed
+to standard error, and the tool returns 1.
+