[llvm-commits] [PATCH] Add Pattern ID Information

[Jakob Stoklund Olesen]

On Aug 4, 2011, at 2:09 PM, David A. Greene wrote:

> Jakob Stoklund Olesen <stoklund at 2pi.dk> writes:
> 
>> On Aug 4, 2011, at 6:35 AM, David A. Greene wrote:
> 
>>> Because sometimes multiple patterns map to an instruction.  Think of
>>> Pat<> patterns.  It's helpful to know which pattern matched to generate
>>> the instruction.
>> 
>> That sounds like something you could dump on dbgs() during isel.
> 
> Because there's so much debug output from isel already.  Debug output in
> isel does not adequately show the context surrounding a particular
> instruction sequence.  If I'm looking at asm output trying to figure out
> why a particular sequence of instructions was picked, it's very hard to
> try to find the appropriate spot in isel debug output where that
> information gets dumped.

Cleaning up isel debug output would be great. It is way too noisy.

> It's really very difficult to map a piece of an asm file back to the
> isel debug output related to it.

That also applies to DAG combine, scheduling, and even InstCombine.

What makes isel special?

>> Why does it need to reserve space in a critical data structure so it
>> can be emitted after codegen?
> 
> See above.
> 
> Note that there is no space penalty for hosts with 64-bit pointers.  For
> hosts with 32-bit pointers it will probably vary somewhat.
> 
> If space is a concern, I'll put an NDEBUG guard around it.  That's not
> ideal but it should adequately address that particular objection.

It is more of a design concern.

Debugging isel should be supported by isel, not MachineInstr and AsmPrinter at the far end of the code generator.

I completely agree that the current isel output is bad. Your help in cleaning that up would be appreciated.

/jakob