[Docs] Mention clone depth feature of git in LLVM getting started

[xgupta]

Summary

The current size of the llvm-project repository exceeds 1 GB. A shallow clone can save a lot of space and time. Some developers might not aware of this feature.

[awarzynski]

Thank you for sending this - I frequently use shallow clones!

I have a small suggestion. How about this:

* To save storage and speed-up the checkout time, you may want to do a `shallow clone <https://git-scm.com/docs/git-clone#Documentation/git-clone.txt---depthltdepthgt>`_. For example, to get the latest revision of the LLVM project, use ``git clone --depth 1 https://github.com/llvm/llvm-project.git``

[xgupta]

Thanks @awarzynski for reviewing! your wording is more correct.

[awarzynski]

I quickly compared shallow vs deep clones (this by no means thorough):

• deep clone: ~6mins, ~2.5GB
• shallow clone: ~1.5mins, ~1.2GB

So clearly this is a very useful recommendation.

LGTM, thanks for working on this! @jyknight was the last person to touch this bit of documentation - he might have some comments/pointers. Could you wait a day or two before merging?

[xgupta]

In D97118#2578727, @awarzynski wrote:

I quickly compared shallow vs deep clones (this by no means thorough):

• deep clone: ~6mins, ~2.5GB
• shallow clone: ~1.5mins, ~1.2GB

Don't know how you did it, but on system shallow clone with 'git clone --depth 1 https://github.com/<username>/llvm-project.git command download 142.44 MiB. (and internet speed is ofcourse less ):

LGTM, thanks for working on this! @jyknight was the last person to touch this bit of documentation - he might have some comments/pointers. Could you wait a day or two before merging?

Sure!

[awarzynski]

In D97118#2578757, @xgupta wrote:

Don't know how you did it, but on system shallow clone with 'git clone --depth 1 https://github.com/<username>/llvm-project.git command download 142.44 MiB. (and internet speed is ofcourse less ):

Sorry, I was referring to the space the repo consumes after unpacking. You are right, only ~140MBs are downloaded. I should've been clearer!

[xgupta]

Sorry, I was referring to the space the repo consumes after unpacking. You are right, only ~140MBs are downloaded. I should've been clearer!

No worries :-) My mind just thinks more about internet data uses than hard drive storage.

llvm/docs/GettingStarted.rst

 
 This is an example workflow and configuration to get and build the LLVM source:
 
 #. Checkout LLVM (including related subprojects like Clang):
 
    * ``git clone https://github.com/llvm/llvm-project.git``
    * Or, on windows, ``git clone --config core.autocrlf=false
      https://github.com/llvm/llvm-project.git``
+   * To save storage and speed-up the checkout time, you may want to do a 
+     `shallow clone <https://git-scm.com/docs/git-clone#Documentation/git-clone.txt---depthltdepthgt>`_. 
+     For example, to get the latest revision of the LLVM project, use 
+     ``git clone --depth 1 https://github.com/llvm/llvm-project.git``
 
 #. Configure and build LLVM and Clang:
 
    * ``cd llvm-project``
    * ``mkdir build``
    * ``cd build``
    * ``cmake -G <generator> [options] ../llvm``