[PATCH] D138995: [CodeView] Add support for local S_CONSTANT records

Thu Dec 1 04:18:19 PST 2022

thieta added a comment.

In D138995#3961742 <https://reviews.llvm.org/D138995#3961742>, @aganea wrote:

> Thanks, that's a nice improvement! Out of curiosity does this optimization happen at `-O0` too? (when using clang-cl)
> Does MSVC generate `S_CONSTANT` as well for your test-case?

In general -O0 doesn't have this problem. I have seen it happen, but unsure what triggers it.

No MSVC doesn't generate S_CONSTANTS for any of my cases. They only use it when you actually do a constant, in most of the cases MSVC doesn't output anything or outputs a S_LOCAL with the optimized away flag set. I tried with /Zo as well and couldn't get it do anything differently.

I even tried to debug several programs with msvc and their default flags, and with /O2 <https://reviews.llvm.org/owners/package/2/> they always had same debugging info as clang-cl.
They do behave better with /O2 <https://reviews.llvm.org/owners/package/2/>, mostly because clang really don't want to emit all declarations if they are global and can const propagate some variables.

Repository:
  rG LLVM Github Monorepo

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https://reviews.llvm.org/D138995