[PATCH] D68945: [DebugInfo] Don't translate dbg.addr and similar intrinsics into indirect DBG_VALUEs

[Jeremy Morse via Phabricator via llvm-commits]

jmorse added a comment.

Adrian wrote:

> Sounds like the problem here is that we don't encode the difference between Memory locations and Register locations in DIExpression and/or DBG_VALUE. I think we currently decide the very late in DwarfExpression.cpp.

Yeah, I've been bitten by this in the past, sometimes adding an extra DW_OP_deref to the end of an expression causes no change to the output DWARF because DwarfExpression.cpp was already guessing the location type ("unknown" -> memory). Particularly awkward is that adding any opcode might implicitly add a deref, if DwarfExpression.cpp starts interpreting the expression as a memory location rather than register location. Unless the expression is already an implicit location, in which case you don't get that extra deref!

> (But we do have DW_OP_stack_value). Maybe we need a DW_OP_LLVM_memory_value, or rename this flag?

IMHO, YMMV, it would be better to head in the other direction and abandon what "kind" of location we have in the compilation stages, because it's a DWARF encoding detail. That would mean adding an opcode to a DIExpression always meant the same thing, with no flags to change their interpretation. Location kinds would have to be decided by DwarfExpression.cpp, something like:

- All expressions ending in a deref are memory locations
- Anything else not ending in a deref that performs some kind of computation is an implicit location
- An empty expression is interpreted as a register location


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https://reviews.llvm.org/D68945