[PATCH] D55900: [MC] Enable .file support on COFF and diagnose it on unsupported targets

Wed Dec 19 13:57:20 PST 2018

rnk added a comment.

In D55900#1336824 <https://reviews.llvm.org/D55900#1336824>, @mstorsjo wrote:

> > However, COFF actually does have some support for this directive, and if you emit an object file, llvm-mc does not assert.
>
> I'm not sure I'm following here - if you emit a COFF object file, from what source? From normal LLVM IR CodeGen, or from MC assembly with a `.file` directive?

>From a .s file with a .file directive.

>> When emitting a COFF object, MC will take those file names and create "debug" symbol table entries for them.
> 
> In which cases are these emitted - only if debug info is enabled?

It seems LLVM's AsmPrinter always emits .file if the target supports it, regardless of debug info. If the directive is emitted, then the file appears in the symbol table.

> Also I'm a bit confused by the test added - doesn't this test check that it errors out, while the flag that is set to true in `MCAsmInfoCOFF` makes this directive be handled so it shouldn't error out after all?

The test is for MachO, which would crash without the new diagnostic code. The new diagnostic code breaks an existing COFF test (llvm/test/MC/COFF/file.s) unless we change COFFMCAsmInfo to support .file.

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  https://reviews.llvm.org/D55900/new/

https://reviews.llvm.org/D55900