[PATCH] D105025: [1/2][LiveDebugVariables] Avoid reduntant DBG_VALUEs after virtregrewrite

[Jeremy Morse via Phabricator via llvm-commits]

jmorse added a comment.

This sounds great to me -- suppressing redundant DBG_VALUEs is a good aim. I'm slightly worried about performance however: in D94981 <https://reviews.llvm.org/D94981> a patch landed to cover a scenario where findInsertLocation was repeatedly stepping back over every debug instruction at the start of a block, effectively becoming quadratic-complexity. Wouldn't looking back over every DBG_VALUE already inserted, when inserting a new one, become quadratic too?

Possibly the solution is to act like D94981 <https://reviews.llvm.org/D94981>, and build a temporary cache of "DBG_VALUEs already inserted at this SlotIdx".



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Comment at: llvm/test/DebugInfo/X86/livedebugvars-avoid-duplicates.ll:4
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+; RUN: llc -O2 %s -stop-before=livedebugvalues -o - | FileCheck %s
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This is running quite a lot of llc, to then hit a fair specific scenario (DBG_VALUE then frame-setup), which makes me worry that it'll be fragile. Would it be sufficient to just check that there are two DBG_VALUEs in the output MIR, and that's it?

(Also, hard-coded metadata numbers)


Repository:
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  https://reviews.llvm.org/D105025/new/

https://reviews.llvm.org/D105025