[LLVMdev] Opinions Wanted: New asm Comments

David A. Greene
Tue, 12 Jul 2011 14:45:23 -0000

Chris Lattner <clattner at apple.com> writes:

>> Is a new flag appropriate for this or should I just put it under
>> -asm-verbose with everything else?  If we want a new flag, does anyone
>> have a spelling they'd recommend?  I'm not particularly fond of
>> -asm-pattern but it was the best concise name my uncreative brain could
>> conjur up.
>
> How do you plan to implement this?  This is a compiler-hacker-only
> feature, can it be protected fully in !NDEBUG code?

The codegen portion certainly can be protected with !NDEBUG.

The change has two parts: a TableGen enhancement to output a table of
pattern strings and some code to pair up MachineInstrs with the
appropriate index into the pattern string table and an AsmPrinter
portion to actually print the comments.

The latter can be easily controlled via NDEBUG.  The former is more
difficult since at the time TableGen is run we don't know how the rest
of the compiler will be built.

How would you prefer this work?  Even if the output were controlled by
NDEBUG, I feel the added pattern comments make the asm file too
cluttered even for day-to-day compiler developers.  This is really a
feature to debug instruction selection problems.  That's why I put it
under the control of a separate option.

                               -Dave