[PATCH] D41669: Teach ValueMapper to use ODR uniqued types when available

[Duncan P. N. Exon Smith via Phabricator via llvm-commits]

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This is unsound, as it breaks CloneModule: it causes the original/cloned module to reference GlobalValues from the new module (composite types transitively reference global values when a type has "interesting" template parameters). See https://bugs.llvm.org/show_bug.cgi?id=48841 (especially https://bugs.llvm.org/show_bug.cgi?id=48841#c22, where I have a long explanation).

@tejohnson, can you share more context about why this was necessary? How is ThinLTO using the value mapper that this happens?

There should be another way to get this optimization that's sound, but I think it'll involve priming the ValueToValueMap that gets sent into MapValue / MapMetadata.


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  rL LLVM

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https://reviews.llvm.org/D41669