[llvm] [LiveDebugVariables] Stop holding SlotIndexes for erased instructions (PR #224467)

[Petar Jovanovic via llvm-commits]

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@@ -2,9 +2,11 @@
 
 # There should be multiple debug values for this variable after regalloc. The
 # value has been spilled, but we shouldn't lose track of the location because
-# of this.
+# of this. Two consecutive DBG_VALUEs naming the same location are redundant,
+# as the first is overridden before it covers anything.
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petar-jovanovic wrote:

Done, with one correction: the second DBG_VALUE overrides the first, which is why losing the first is safe. What canonicalizeIndexes() does is merge the intervals so only one is emitted. I worded it that way in both tests now.

https://github.com/llvm/llvm-project/pull/224467