[clang] [llvm] [DLCov 2/5] Implement DebugLoc coverage tracking (PR #107279)

[David Blaikie via cfe-commits]

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@@ -169,6 +169,47 @@ See the discussion in the section about
 :ref:`merging locations<WhenToMergeLocation>` for examples of when the rule for
 dropping locations applies.
 
+.. _NewInstLocations:
+
+Setting locations for new instructions
+--------------------------------------
+
+Whenever a new instruction is created and there is no suitable location for that
+instruction, that instruction should be annotated accordingly. There are a set
+of special ``DebugLoc`` values that can be set on an instruction to annotate the
+reason that it does not have a valid location. These are as follows:
+
+* ``DebugLoc::getCompilerGenerated()``: This indicates that the instruction is a
+  compiler-generated instruction, i.e. it is not associated with any user source
+  code.
+
+* ``DebugLoc::getDropped()``: This indicates that the instruction has
+  intentionally had its source location removed, according to the rules for
+  :ref:`dropping locations<WhenToDropLocation>`; this is set automatically by
+  ``Instruction::dropLocation()``.
+
+* ``DebugLoc::getUnknown()``: This indicates that the instruction does not have
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dwblaikie wrote:

Wonder whether it's worth splitting these cases from "there could be a right answer here, but it's Too Hard(tm) to find it right now" (places to look to fix bugs/improve location coverage) from "this is unrepresentable" (places that would benefit from representational changes, but aren't otherwise fixable)

But I don't feel strongly about it.

Otherwise the doc changes look good to me

https://github.com/llvm/llvm-project/pull/107279