Clang ignoring some (or all?) warning flags on my Windows machine

[Jamie Madill]

I am exprimenting with a diagnostic flag -Wpadded. I've found that on my Windows Clang for some reason I don't see warnings for obvious violations.

Experimented with this source:

#include <stdio.h>
struct s {
char c;
int i;
};
int main() {
s s1 = {};
printf("%zu\n", sizeof(s1));
return 0;
}

On Windows:

$ third_party/llvm-build/Release+Asserts/bin/clang-cl.exe test.cpp -Wpadded
$ ./test
8

Clearly there was some padding going on. On Linux:

$ third_party/llvm-build/Release+Asserts/bin/clang test.cpp -Wpadded
/usr/local/google/home/jmadill/temp/test.cpp:6:6: warning: padding struct 's' with 3 bytes to align 'i' [-Wpadded]
        int i;
            ^
1 warning generated.

Anyone know how/if I can get this error to show up with the Windows Clang in Chrome? Was trying to add this to ANGLE.

Thanks,

Jamie

[Reid Kleckner]

The issue is that the warning is not implemented in the MS C++ ABI specific record layout codepath. I filed a bug for it here: https://bugs.llvm.org/show_bug.cgi?id=39423

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[Nico Weber]

I think this warning isn't implemented in clang's microsoft codegen -- all references to warn_padded_struct_ in http://llvm-cs.pcc.me.uk/tools/clang/lib/AST/RecordLayoutBuilder.cpp#1922 are in ItaniumRecordLayoutBuilder ("itanium" meaning basically "not windows"). If you want this, can you file a bug please?

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[Jamie Madill]

Cool, thanks the responses & Reid for filing the issue!