[Docs][llvm-link] Add documentation an CLI options

[aidengrossman]

Summary

Currently the documentation on the command line options for llvm-link is quite sparse. This patch adds in the options that the tool understands that aren't currently present in the documentation.

[aidengrossman]

Was trying to reference the online documentation to look at some flags but didn't see the options that I was looking for and had to go digging through the source code to find it, so I decided to write up a patch. I've added all the missing options which might not be completely ideal as there are quite a few that have been implemented mainly to be used for llvm-lit tests rather than for public consumption, but I felt like there wasn't a large reason not to include them. Definitely interested in hearing other opinions though.

[aidengrossman]

Ping on this patch when reviewers have a chance. Thanks!

[tejohnson]

lgtm with a clarification suggested below.

llvm/docs/CommandGuide/llvm-link.rst

86

maybe: "Specify the path to a file containing the module summary index with the results of an earlier ThinLTO link. Required with -import." (i.e. make it clearer that llvm-link is not itself doing the ThinLTO link, but this file should have the results of one done earlier).

[MaskRay]

llvm/docs/CommandGuide/llvm-link.rst

60

For user-facing utilities (llvm-link is probably not yet), we advertise double-dash long options.

[aidengrossman]

llvm/docs/CommandGuide/llvm-link.rst

60

Just to be clear, you're saying that we should keep the single-dash long options here? Or do you want me to change the documentation to use double-dash long options?

[MaskRay]

llvm/docs/CommandGuide/llvm-link.rst

60

Yes, consider documenting just double-dash long options.

[aidengrossman]

Address reviewer feedback.

• Update message for --summary-index
• Use double dash long messages

[aidengrossman]

@MaskRay If you don't mind taking a look at this and making sure my most recent changes matches what you expect.

There are also quite a few other tools (maybe even most) that are still using single-dash options in their documentation. I'll probably open up some patches to fix that so the documentation is more consistent in a little bit.

llvm/docs/CommandGuide/llvm-link.rst

 
  Write output in LLVM intermediate language (instead of bitcode).
 
 .. option:: -d
 
  If specified, :program:`llvm-link` prints a human-readable version of the
  output bitcode file to standard error.
 
-.. option:: -help
+.. option:: --help
 
  Print a summary of command line options.
 
 .. option:: -v
 
  Verbose mode.  Print information about what :program:`llvm-link` is doing.
  This typically includes a message for each bitcode file linked in and for each
  library found.
 
+.. option:: --override <filename>
+
+  Adds the passed-in file to the link and overrides symbols that have already
+  been declared with the definitions in the file that is passed in. This flag
+  can be specified multiple times to have multiple files act as overrides. If
+  a symbol is declared more than twice, the definition from the file declared
+  last takes precedence.
+
+.. option:: --import <function:filename>
+
+  Specify a function that should be imported from the specified file for
+  linking with ThinLTO. This option can be specified multiple times to import
+  multiple functions.
+
+.. option:: --summary-index <filename>
+
+  Specify the path to a file containing the module summary index with the
+  results of an earlier ThinLTO link. This option is required when 
+  `--import` is used.
+
+.. option:: --internalize
+
+  Internalize the linked symbols.
+
+.. option:: --disable-debug-info-type-map
+
+  Disables the use of a uniquing type map for debug info.
+
+.. option:: --only-needed
+
+  Link only needed symbols.
+
+.. option:: --disable-lazy-loading
+
+  Disable lazy module loading.
+
+.. option:: --suppress-warnings
+
+  Suppress all linker warnings.
+
+.. option:: --preserve-bc-uselistorder
+  
+  Preserve the use-list order when writing LLVM bitcode.
+
+.. option:: --preserve-ll-uselistorder
+
+  Preserve the use-list order when writing LLVM assembly.
+
+.. option:: --ignore-non-bitcode
+
+  Do not error out when a non-bitcode file is encountered while processing
+  an archive.
+
 EXIT STATUS
 -----------
 
 If :program:`llvm-link` succeeds, it will exit with 0.  Otherwise, if an error
 occurs, it will exit with a non-zero value.