[PATCH] D56151: [DebugInfo] PR40010: Avoid register coalesing altering DBG_VALUE valuations

[Jeremy Morse via Phabricator via llvm-commits]

jmorse added a comment.

Hi,

In D56151#1558161 <https://reviews.llvm.org/D56151#1558161>, @aprantl wrote:

> I'm reading this as: "this patch make debug info more accurate by rejecting invalid DBG_VALUEs earlier on, but it overshoots the target a bit and also rejects a few(?) false positives". I support this approach, as we all want to move LLVM into the "more accurate" direction, assuming that the false positives are fixable and the ratio of rejected incorrect DBG_VALUEs to false positives is favorable.


Exactly that; on x86_64 at least from my comment here [0] the loss in variable locations is small (possibly it's larger for Bjorns arch?), but the false-positives are very obvious to the human eye, which is annoying. I don't have a feeling for the true/false ratio (I can dig into it), but again the impact is small.

(As I recall, there was no way to detect the false-positives without adding a new MachineDominatorTree analysis, which seemed excessive when we shouldn't be generating the faulty DBG_VALUEs in the first place).

[0] https://reviews.llvm.org/D56151#1346195


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