> No, it isn't. Expanders call other expanders to do fancy stuff. When > everything is done, they tag a REG_EQUAL note on the last insn. > One of the purposes of set_unique_reg_note is lubricate this process: > the layered expanders can add multiple REG_EQUAL notes. We only want > the most high-level note, so we discard the previous one from the > next lower level. Well, we realize now that we only want the most > high-level note that makes sense, actually. We either have to make it > make sense, or abandon adding it.
This would have been a valid design 20 years ago when notes were implemented. But, for the past couple of decades, set_unique_reg_note hasn't touched the datum and all bugs over the years in this area have been fixed in the caller. So this one should be fixed the same way, I see no reason to special-case it. > If every expander has to analyze the instructions that have been issued > to figure out if the new note needs to be modified, or cannot be applied > at all, you end up with umpteen duplications of the checks I added to > set_unique_reg_note prepended to its call sites. Yes, expanders must know what they're doing, but this isn't new. -- Eric Botcazou
