[llvm] Restore lost nuance in DeveloperPolicy regarding input languages for test cases (PR #79527)

[Daniel Sanders via llvm-commits]

https://github.com/dsandersllvm created https://github.com/llvm/llvm-project/pull/79527

While re-reading the various policies for changes I've missed, I noticed that the policy on test cases had been rewritten to be a bit overly restrictive and not accurately reflect the test cases in LLVM today.

Back in 2019 (git: e0ddc731a4ad3, svn: 201619), some references to llvm-gcc were removed from the DeveloperPolicy. One of these removals removed some important nuance along with the example that referenced llvm-gcc. The original text was:
> * Test cases should be written in `LLVM assembly language <LangRef.html>`_ unless the feature or regression being 
> tested requires another language (e.g. the bug being fixed or feature being implemented is in the llvm-gcc C++ front-end, > in which case it must be written in C++).

and this was reduced to:
> * Test cases should be written in :doc:`LLVM assembly language <LangRef>`. which is a bit too definite and restrictive.

This commit attempts to restore the original intent but with examples that exist in the current LLVM source.

>From 84ef3a66d5e27178c953d8aa07e0760ab7a70db5 Mon Sep 17 00:00:00 2001
From: Daniel Sanders <daniel_l_sanders at apple.com>
Date: Thu, 25 Jan 2024 15:59:18 -0800
Subject: [PATCH] Restore lost nuance in DeveloperPolicy w.r.t input languages
 for test cases

While re-reading the various policies for changes I've missed, I noticed
that the policy on test cases had been rewritten to be a bit overly
restrictive and not accurately reflect the test cases in LLVM today.

Back in 2019 (git: e0ddc731a4ad3, svn: 201619), some references to llvm-gcc
were removed from the DeveloperPolicy. One of these removals removed some
important nuance along with the example that referenced llvm-gcc. The
original text was:
> * Test cases should be written in `LLVM assembly language <LangRef.html>`_
>   unless the feature or regression being tested requires another language
>   (e.g. the bug being fixed or feature being implemented is in the llvm-gcc
>   C++ front-end, in which case it must be written in C++).
and this was reduced to:
> * Test cases should be written in :doc:`LLVM assembly language <LangRef>`.
which is a bit too definite and restrictive.

This commit attempts to restore the original intent but with examples that
exist in the current LLVM source.
---
 llvm/docs/DeveloperPolicy.rst | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/llvm/docs/DeveloperPolicy.rst b/llvm/docs/DeveloperPolicy.rst
index f49b5b13378ea21..d8655175beb8c86 100644
--- a/llvm/docs/DeveloperPolicy.rst
+++ b/llvm/docs/DeveloperPolicy.rst
@@ -209,7 +209,11 @@ features added.  Some tips for getting your testcase approved:
   directory. The appropriate sub-directory should be selected (see the
   :doc:`Testing Guide <TestingGuide>` for details).
 
-* Test cases should be written in :doc:`LLVM assembly language <LangRef>`.
+* Test cases should be written in the closest, most directly supported input
+  language for the component being tested. This is usually
+  :doc:`LLVM assembly language <LangRef>` but there are some exceptions such as
+  assembly for MC layer tests, or in some cases a choice is available such
+  LLVM assembly language or MIR for GlobalISel tests.
 
 * Test cases, especially for regressions, should be reduced as much as possible,
   by :doc:`bugpoint <Bugpoint>` or manually. It is unacceptable to place an