[llvm] Refine the examples in the debug info document (PR #86272)

[Shan Huang via llvm-commits]

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@@ -91,8 +91,12 @@ misattributed to a block containing one of the instructions-to-be-merged.
 
 Examples of transformations that should follow this rule include:
 
-* Merging identical loads/stores which occur on both sides of a CFG diamond
-  (see the ``MergedLoadStoreMotion`` pass).
+* Hoisting identical instructions from successors of a conditional branch or
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Apochens wrote:

Actually, the merging updater (eg., `applyMergedLocation`) will drop the specific row or column number in the debug location when merging different `DebugLoc`s, only keeping their common scope. As a result, the merged debug location would not provide "extra coverage". Moreover, instructions of different predecessors (ie., at least two instructions) are sunk only when they are all identical (for now, I haven't seen any exception). So, I think it's not necessary.

https://github.com/llvm/llvm-project/pull/86272