[llvm-dev] Debug information with clang-cl on Windows

Reid Kleckner via llvm-dev llvm-dev at lists.llvm.org
Wed Mar 10 12:38:10 PST 2021

I'm glad to hear things are working reasonably well for you. :)

Regarding variables marked as optimized out, the main issue that I'm aware
of has to do with parameters at function entry. We had a user report this
as https://crbug.com/755841.

What you have in the screenshot doesn't seem related to parameters. It
seems like this issue could be specific to 32-bit x86. We can definitely
take a look at a more detailed bug report if you find the time to file one,
but as Adrian mentioned, 64-bit is becoming the better tested, more robust,


On Tue, Mar 9, 2021 at 12:37 AM Tobias Hieta via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Hello,
> We recently switched our windows builds from the CL compiler to
> clang-cl. This was a pretty big jump in terms of code generation and
> having a uniform compiler across all the major platforms.
> Our setup is that our Windows developer use MSVC as the IDE and
> compile with our own build of clang-cl and link with lld-link.
> Some of the developers noticed that some of the debug information are
> not as good as with CL. Or rather some variables seems to be optimized
> out, this is what the IDE says, see attached screenshot. I have tried
> to figure out if there is a rhyme and reason to what variables are
> gone - but I have not been able to see any pattern.
> Our command line is:
> clang-cl.exe /nologo -DUNICODE -DUSE_BREAKPAD -DWIN32
> -Iincludes -m32 -fdiagnostics-absolute-paths
> --target=i686-windows-msvc -m32 /DWIN32 /D_WINDOWS /GR /EHsc /Zi /Ob0
> /Od /RTC1 -MDd /Zm512 /EHsc /bigobj /W3 -Werror -Wsign-compare
> -Wno-reorder-ctor -Wno-delete-non-virtual-dtor -Wunused-variable
> -Wuninitialized -std:c++14
> Is there any good way to debug this or is it a known limitation with
> clang-cl or 32 bit (we don't do 64 yet - but with clang-cl we hope to
> move towards that soon). Or am I missing some flags?
> Thanks,
> Tobias
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