match_scratch causing pattern mismatch

[Paul Shortis]

Of course, the answer is to

         emit_insn( gen_comparesi3( op0, op1 ));

which generates the required match_scratch

instead of ...

   cmpmode = SELECT_CC_MODE( branchCode, op0, op1 );
   flags = gen_rtx_REG ( cmpmode, CC_REGNUM );

   compare = gen_rtx_COMPARE ( cmpmode, op0, op1 );
   emit_insn( gen_rtx_SET( VOIDmode, flags, compare ));

Sorry for the bother...

On 31/07/15 08:39, Paul Shortis wrote:
> in a GCC port to a 16 bit cpu that uses CC flags for branching, I'm 
> experimenting with using a 32 bit subtract for compare instead of 
> multiple 16 bit compares and branches.
>
> my cbranch<mode>4 expander produces a compare and conditional branch 
> patterns...
>
>   cmpmode = SELECT_CC_MODE( branchCode, op0, op1 );
>   flags = gen_rtx_REG ( cmpmode, CC_REGNUM );
>
>   compare = gen_rtx_COMPARE ( cmpmode, op0, op1 );
>   emit_insn( gen_rtx_SET( VOIDmode, flags, compare ));
>
> To implement compare using a subtract I need a HI mode scratch 
> register, so I used a match_scratch
>
> (define_insn "comparesi3"
>   [ (set (reg:CC CC_REGNUM)
>             (compare:CC (match_operand:SI 0 "register_operand" "r,r")
>                                   (match_operand:SI 1 "rhs_operand" 
> "r,i")))
>    (clobber(match_scratch:HI 2 "=r,r"))
>   ]
>   ""
>
>
> When I do this, the compare no longer matches and I get failures like 
> this in the vregs pass...
>
> ../../../libgcc/unwind-dw2.c:1224:1: error: unrecognizable insn:
>  }
>  ^
> (insn 69 68 70 7 (set (reg:CC 16 flags)
>         (compare:CC (reg:SI 44 [ D.5851 ])
>             (reg:SI 169))) ../../../libgcc/unwind-dw2.c:972 -1
>      (nil))
>
> when I remove the match_scratch these errors disappear, but of course 
> I don't have the scratch register needed to implement the proper 
> assembler instructions
>
> I'm aware that it's the combiner that understands clobbers etc. So, in 
> the .md file I tried to add a dummy comparesi3 pattern that doesn't 
> have the match_scratch... after the pattern containing the 
> match_scratch. This sometimes works, however on occasion the dummy 
> pattern is selected by the combiner instead of the match_scratch 
> pattern .
>
> Any insight appreciated...
>
> Cheers, Paul
>