llvm dev - Jun 2008 - [LLVMdev] Implementing llvm.atomic.cmp.swap.i32 on PowerPC

Hi all,

I'm trying to figure out how to add the instructions required for
llvm.atomic.cmp.swap.i32 on PowerPC.  I figured out LWARX (patch
attached) but the other two (CMP_UNRESw and STWCX) require multiple
instructions:

  let Defs = [CR0] in {
  def STWCX : Pseudo<(outs), (ins GPRC:$rS, memrr:$dst, i32imm:$label),
                    "stwcx. $rS, $dst\n\tbne-
La${label}_entry\nLa${label}_exit:",
                     [(PPCstcx GPRC:$rS, xoaddr:$dst, imm:$label)]>;
  
  def CMP_UNRESw : Pseudo<(outs), (ins GPRC:$rA, GPRC:$rB, i32imm:$label),
                           "cmpw $rA, $rB\n\tbne- La${label}_exit",
                           [(PPCcmp_unres GPRC:$rA, GPRC:$rB, imm:$label)]>;
  }

...and I can't figure out the syntax for that.  Any suggestions?

Cheers,
Gary

-- 
http://gbenson.net/
-------------- next part --------------
Index: lib/Target/PowerPC/PPCInstrInfo.td
==================================================================---
lib/Target/PowerPC/PPCInstrInfo.td	(revision 52823)
+++ lib/Target/PowerPC/PPCInstrInfo.td	(working copy)
@@ -531,8 +531,8 @@
                       PPC970_DGroup_Single;
 
 // Atomic operations.
-def LWARX : Pseudo<(outs GPRC:$rD), (ins memrr:$ptr, i32imm:$label),
-                   "\nLa${label}_entry:\n\tlwarx $rD, $ptr",
+def LWARX : XForm_1<31,  20, (outs GPRC:$rD), (ins memrr:$ptr,
i32imm:$label),
+                   "\nLa${label}_entry:\n\tlwarx $rD, $ptr",
LdStLWARX,
                    [(set GPRC:$rD, (PPClarx xoaddr:$ptr, imm:$label))]>;
 
 let Defs = [CR0] in {

On Jun 27, 2008, at 8:27 AM, Gary Benson wrote:
>  def CMP_UNRESw : Pseudo<(outs), (ins GPRC:$rA, GPRC:$rB, i32imm: 
> $label),
>                           "cmpw $rA, $rB\n\tbne-
La${label}_exit",
>                           [(PPCcmp_unres GPRC:$rA, GPRC:$rB, imm: 
> $label)]>;
>  }
>
> ...and I can't figure out the syntax for that.  Any suggestions?
Hi Gary,

You have to write custom encoding logic in C++ for this.  This should  
go in PPCCodeEmitter::emitBasicBlock.  I admit this isn't very  
elegant.  A better solution would be to fix the lowering to produce  
two instructions instead of this pseudo instruction.

-Chris

Chris Lattner wrote:
> On Jun 27, 2008, at 8:27 AM, Gary Benson wrote:
> >  def CMP_UNRESw : Pseudo<(outs), (ins GPRC:$rA, GPRC:$rB, i32imm: 
> > $label),
> >                           "cmpw $rA, $rB\n\tbne-
La${label}_exit",
> >                           [(PPCcmp_unres GPRC:$rA, GPRC:$rB, imm: 
> > $label)]>;
> >  }
> >
> > ...and I can't figure out the syntax for that.  Any suggestions?
> 
> You have to write custom encoding logic in C++ for this.  This
> should go in PPCCodeEmitter::emitBasicBlock.  I admit this isn't
> very elegant.  A better solution would be to fix the lowering to
> produce two instructions instead of this pseudo instruction.
Hi Chris,

I'd prefer to fix the lowering if possible; the pseudo instructions
are only used in three places, so it shouldn't be a huge change.
I need to generate labels in PPCTargetLowering::LowerAtomicCMP_SWAP
however: how do I do that?  FWIW the code it needs to emit is:

  ; inputs: ptr, oldval, newval
  loop:
        lwarx $tmp, 0, $ptr
        cmpw $oldval, $tmp
        bne- exit
        stwcx. $newval, 0, $ptr
        bne- loop
  exit:
        ...


Cheers,
Gary

-- 
http://gbenson.net/