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

[Adrian Prantl via llvm-commits]

================
@@ -417,8 +448,9 @@ values through compilation, when objects are promoted to SSA values an
 ``llvm.dbg.value`` intrinsic is created for each assignment, recording the
 variable's new location. Compared with the ``llvm.dbg.declare`` intrinsic:
 
-* A dbg.value terminates the effect of any preceding dbg.values for (any
-  overlapping fragments of) the specified variable.
+* A dbg.value terminates the effect of any preceding dbg.values for any
+  spatially overlapping variables or fragments of the specified variable or
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adrian-prantl wrote:

The way this is worded sounds as if in this example:
```
%1 = ...
call llvm.dbg.value(metadata %1, DILocalVariable("x"), DIExpression())
%2 = ...
call llvm.dbg.value(metadata %1, DILocalVariable("y"), DIExpression())
```
The second intrinsic ends the range of "x", but that's not the case. It only terminates it if it refers to the _same_ variable or a fragment of it.

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