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Re: Extending constraints using register subclasses

----- Original Message ----
> From: Jamie Prescott <>
> To: Michael Meissner <>
> Cc:
> Sent: Thursday, May 14, 2009 4:22:13 PM
> Subject: Re: Extending constraints using register subclasses
> OK, I tried reordering the classes by putting smaller ones first. Did not work.
> As far as IRA_COVER_CLASS, this should be a new thing, isn't it? I'm currently
> on 4.3.3 and I found no mention of it anywhere.

OK, the problem is in reg_fits_class_p().

void dseek(unsigned int offset)
        asm volatile ("dsk r56\n\t":: "a2" (offset));

The r56 register is part of GENERAL_REGS (0..64) and 'a2' is 'r2', that is a subclass (R2_REG)
of GENERAL_REGS containing only one register.
In recog.c, in the 'default' switch handling, there's a call to the REG_CLASS_FROM_CONSTRAINT()
that I hooked, to return R2_REG upon 'a2'.
That code ends up calling reg_fits_class_p() with 'operand' being the r0 REG RTX, and 'cl' being R2_REG.
Such function tests if r0 is inside R2_REG, that obviously isn't, and fails.

- Jamie


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