[llvm] [LangRef] Clarify definition of fragments and debug intrinsics (PR #82019)

[Stephen Tozer via llvm-commits]

================
@@ -130,6 +130,40 @@ debugging information influences optimization passes then it will be reported
 as a failure.  See :doc:`TestingGuide` for more information on LLVM test
 infrastructure and how to run various tests.
 
+.. _variables_and_variable_fragments:
+
+Variables and Variable Fragments
+================================
+
+Source language variables (or just "variables") are represented by `local
+variable <LangRef.html#dilocalvariable>`_ and `global variable
+<LangRef.html#diglobalvariable>`_ metadata nodes.
+
+When variables are not allocated to contiguous memory or to a single LLVM value
+the metadata must record enough information to describe each "piece" or
----------------
SLTozer wrote:

I agree that the wording could be improved - I think that your proposed wording is better, but might be ambiguous with respect to variadic debug values, which aren't necessarily fragments but may be "described" by many LLVM values. Perhaps "When variables are split up across multiple LLVM values...", and it may also be worthwhile to be direct and give an example, i.e. "...such as for structs that have been split into separate LLVM values for each member...". No particularly strong feelings on this part from my end though!

https://github.com/llvm/llvm-project/pull/82019