[llvm] [CodeLayout] CDSortImpl: remove linear-time erase_value from mergeChains (PR #69276)

[Fangrui Song via llvm-commits]

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@@ -1152,6 +1153,7 @@ class CDSortImpl {
       MergeGainT BestGain = BestEdge->getMergeGain();
       mergeChains(BestSrcChain, BestDstChain, BestGain.mergeOffset(),
                   BestGain.mergeType());
+      --NumHotChains;
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MaskRay wrote:

Thanks for the suggestion. I'll optimize out `HotChains` and rename `NumHotChains` to `NumActiveChains`.

https://github.com/llvm/llvm-project/pull/69276