LLVM-MCA spews "unknown sub-directive" errors with GCC versions > 9.2

https://godbolt.org/z/svnn4xEsG

This is how the MCA output looks like with GCC versions after 9.2:

<source>:12:14: error: unknown sub-directive in '.loc' directive
        .loc 1 4 86 view -0
                    ^
<source>:14:13: error: unknown sub-directive in '.loc' directive
        .loc 1 5 5 view .LVU1
                   ^
<source>:15:13: error: unknown sub-directive in '.loc' directive
        .loc 1 6 5 view .LVU2
                   ^
<source>:16:13: error: unknown sub-directive in '.loc' directive
        .loc 1 7 5 view .LVU3
...

Looks like a probable bug in MCA to me, but could be CE specific.

Edit: GCC 11.2 and current trunk appear to work at first glance, but if you scroll down to the end of the MCA output, the errors are still there: https://godbolt.org/z/4hhW64753

[adibiagio]

Hi,

Apologies for the very late reply.

I found the following options from https://gcc.gnu.org/onlinedocs/gcc/Debugging-Options.html

-gas-locview-support
Inform the compiler that the assembler supports view assignment and reset assertion checking in .loc directives.

This option will be enabled by default if, at GCC configure time, the assembler was found to support them.

-gno-as-locview-support
Force GCC to assign view numbers internally, if -gvariable-location-views are explicitly requested.

Strictly speaking, I don’t think this is an llvm-mca issue. It is more like llvm libraries don’t know how to parse these new “view assignment and reset assertion checking in .loc directives”.

As a workaround, you can pass -gno-as-locview-support to the command line for the gcc build (in your godbolt link). That should generate .loc directives that are compatible with what the llvm asm parser expects to see.

I hope it helps.

Again, apologies for the very late reply.

-Andrea

[TiborGY]

Scratch that, the errors still appear with the latest GCC versions, but for whatever reason they are displayed after the MCA output