On Wed, Dec 21, 2005 at 08:23:17PM +0200, Bernd Jendrissek wrote:
> I've been playing with my 16-bit ix86 port again,
I started coding one from scratch in about October or so. It has been
interesting.
[cut %bx as %bl and %bh in BASE_REGS]
> The simple solution was just to add %bh to BASE_REGS in
> REG_CLASS_CONTENTS; that seemed to take care of the BASE_REGS problem
> for me.
This is actually documented, but I too overlooked that.
> On to the next cluster of problems. I finally got around %cl
> vs %cx (for shift counts) by expanding the shift patterns first into,
> for example,
>
> (define_expand "ashlhi3"
> [(parallel [(set (match_operand:HI 0 "nonimmediate_operand" "")
> (ashift:HI (match_operand:HI 1 "general_operand" "")
> (match_operand:QI 2 "general_operand" "")))
> (clobber (reg:CC FLAGS_REG))])]
> ...
>
> first before recognizing them with define_insn'ed patterns; that seemed
> to do the trick of forcing GCC to "know" that the ix86 shift counts have
> no more than 8 bits of significance (less even, in fact).
I'm having success with a regular define_insn:
(define_insn "<optab_shift><mode>3"
[(set (match_operand:MO 0 "nonimmediate_operand" "=<r>m,<r>m")
(any_shift:MO (match_operand:MO 1 "nonimmediate_operand" "0,0")
(match_operand:QI 2 "nonmemory_operand" "K,CI")))
(clobber (reg:CC CC_REG))]
...
(It uses code and mode macros to get all shifts and rotates in both QImode
and HImode in just one pattern.)
"C" is my constraint letter for %cl. What exactly is the problem you were
having?
The only problem I see is that gcc only uses the HImode version, even when
given something like:
unsigned char a, b, c;
a = b << c;
I have not yet tried to find out why.
> Now I'm on the multiplication patterns, which are widening, for which I
> have:
[snip]
> The "a" register in SImode would in fact be the %dx:%ax pair. I
> suppose I could introduce *yet another* constraint letter and yet
> another class that would contain all of %ax and %dx, but would be used
> only for forcing (reg:SI 0 [ al ]).
That will work. I have "e" (think of %eax) for that purpose.
[snip patches]
> Of course these patches almost certainly only appear to fix my
> *immediate* problem. "The problem" being that I want to be able to tell
> GCC two different things: "I want %dx to be part of an SImode group in
> class AXDXREGS" and "but only %al is useable as an operand". Any ideas?
I don't think I understand what the problem is. If all you want is an SImode
register starting at %al, then simply specify SImode and the contraint letter
for AXDXREGS.
Best regards,
Rask Ingemann Lambertsen
