docs: update documentation for llvm-profdata

[arphaman]

Summary

This patch updates the command line documentation for the llvm-profdata tool.

[arphaman]

Closed by commit rL214331 (authored by @arphaman).

docs/CommandGuide/llvm-profdata.rst

-llvm-profdata - work with profile data
-======================================
+llvm-profdata - Profile data tool
+=================================
 
 SYNOPSIS
 --------
 
-:program:`llvm-profdata` [-output=output] file1 file2
+:program:`llvm-profdata` *command* [*args...*]
 
 DESCRIPTION
 -----------
 
-The experimental :program:`llvm-profdata` tool reads two profile data files
-generated by PGO instrumentation and generates a file with merged data.
+The :program:`llvm-profdata` tool is a small utility for working with profile
+data files.
 
-The profile data format itself is currently textual.
+COMMANDS
+--------
+
+* `merge <profdata_merge_>`_
+* `show <profdata_show_>`_
+
+.. program:: llvm-profdata merge
+
+.. _profdata_merge:
+
+MERGE
+-----
+
+SYNOPSIS
+^^^^^^^^
+
+:program:`llvm-profdata merge` [*options*] [*filenames...*]
+
+DESCRIPTION
+^^^^^^^^^^^
+
+:program:`llvm-profdata merge` takes several profile data files
+generated by PGO instrumentation and merges them together into a single
+indexed profile data file.
 
 OPTIONS
--------
+^^^^^^^
+
+.. option:: -help
+
+ Print a summary of command line options.
+
+.. option:: -output=output, -o=output
+
+ Specify the output file name.  If *output* cannot be - as the resulting
+ indexed profile data can't be written to standard output.
+
+.. program:: llvm-profdata show
+
+.. _profdata_show:
+
+SHOW
+----
+
+SYNOPSIS
+^^^^^^^^
+
+:program:`llvm-profdata show` [*options*] [*filename*]
+
+DESCRIPTION
+^^^^^^^^^^^
+
+:program:`llvm-profdata show` takes a profile data file and displays the
+information about the profile counters for this file and
+for any of the specified function(s).
+
+If *filename* is omitted or is ``-``, then **llvm-profdata show** reads its
+input from standard input.
+
+OPTIONS
+^^^^^^^
+
+.. option:: -all-functions
+
+ Print details for every function.
+
+.. option:: -counts
+
+ Print the counter values for the displayed functions.
+
+.. option:: -function=string
+
+ Print details for a function if the function's name contains the given string.
+
+.. option:: -help
+
+ Print a summary of command line options.
 
-.. option:: -output=output
+.. option:: -output=output, -o=output
 
- This option selects the output filename.  If not specified, output is to
- stdout.
+ Specify the output file name.  If *output* is - or it isn't specified,
+ then the output is sent to standard output.
 
 EXIT STATUS
 -----------
 
-:program:`llvm-profdata` returns 1 if it cannot read input files or there is a
-mismatch between their data.
+:program:`llvm-profdata` returns 1 if the command is omitted or is invalid,
+if it cannot read input files, or if there is a mismatch between their data.