llvm dev - Nov 2011 - [LLVMdev] AsmPrinter vs. MCAsmStreamer

I'm writing a backend using a mid-October svn snapshot of LLVM. I'm
having
a hard time figuring out the relationship between my XXXAsmPrinter and
MCAsmStreamer. Can someone explain what each is responsible for? Looking at
the existing targets, the XXXAsmPrinter implementations seem to implement
both the legacy "create a .s file" behavior, using
printInstruction/printOperand/etc as well as the newer "lower to
MCInst"
behavior (EmitInstruction). Is this just a remnant of the v2.x -> v3.x
transition?

AFAICT, the MCAsmStreamer should be the interface to create the .s file
going forward. Is that true? If true, how does it fit into registering the
asmprinter as a pass? That is, if the AsmPrinter pass is used to lower to
MCInst in the XXXAsmPrinter, then what? What's the target registration for
MCInst -> .s file?

Thanks,
Joe
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On Nov 8, 2011, at 4:23 PM, Joe Matarazzo wrote:
> I'm writing a backend using a mid-October svn snapshot of LLVM. I'm
having a hard time figuring out the relationship between my XXXAsmPrinter and
MCAsmStreamer. Can someone explain what each is responsible for? Looking at the
existing targets, the XXXAsmPrinter implementations seem to implement both the
legacy "create a .s file" behavior, using
printInstruction/printOperand/etc as well as the newer "lower to
MCInst" behavior (EmitInstruction). Is this just a remnant of the v2.x
-> v3.x transition?
> 
The old MachineInstr based AsmPrinter routines are legacy cruft. Not everything
has been moved over to the new way of doing things yet.
> AFAICT, the MCAsmStreamer should be the interface to create the .s file
going forward. Is that true? If true, how does it fit into registering the
asmprinter as a pass? That is, if the AsmPrinter pass is used to lower to MCInst
in the XXXAsmPrinter, then what? What's the target registration for MCInst
-> .s file?
> 
Yes, MCAsmStreamer is the correct path. You shouldn't need to do anything
special to register it. Just the usual LLVMInitializeXXXAsmPrinter() hook. See
the ARM or X86 target for examples.

-Jim