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Re: Bug in binop rotate ?
- From: Richard Guenther <richard dot guenther at gmail dot com>
- To: Andrew Hutchinson <andrewhutchinson at cox dot net>
- Cc: GCC Development <gcc at gcc dot gnu dot org>
- Date: Sat, 17 Oct 2009 16:14:38 +0200
- Subject: Re: Bug in binop rotate ?
- References: <4AD9CAE6.8070404@cox.net>
On Sat, Oct 17, 2009 at 3:47 PM, Andrew Hutchinson
<andrewhutchinson@cox.net> wrote:
> I have been adding rotate capability to AVR port and have come across what I
> think is bug in
> optabs.c: expand_binop()
>
> This occurs during a rotate expansion. For example
>
> target ?= op0 ?rotated by op1
>
> In the particular situation (code extract below) it tries a reverse rotate
> of (bits - op1). Where this expression is expanded as a simple integer,
> a negation or subtraction depending on type of op1 and target.
>
> The expansion of the subtraction is using the mode of the target - I believe
> it should be using the mode of op1.
> The mode of the rotation ?amount need not be the same as the target.
>
> target:DI = Op0:DI rotate op1:HI
>
> In my testcase it is not and I get ?asserts latter in simplfy_rtx.
>
> The negation mode looks equally wrong.
>
> Am I mistaken?
I think you are correct.
Richard.
>
> ?/* If we were trying to rotate, and that didn't work, try rotating
> ? ?the other direction before falling back to shifts and bitwise-or. ?*/
> ?if (((binoptab == rotl_optab
> ? && optab_handler (rotr_optab, mode)->insn_code != CODE_FOR_nothing)
> ? ? ?|| (binoptab == rotr_optab
> ? ? ?&& optab_handler (rotl_optab, mode)->insn_code != CODE_FOR_nothing))
> ? ? && mclass == MODE_INT)
> ? {
> ? ? optab otheroptab = (binoptab == rotl_optab ? rotr_optab : rotl_optab);
> ? ? rtx newop1;
> ? ? unsigned int bits = GET_MODE_BITSIZE (mode);
>
> ? ? if (CONST_INT_P (op1))
> ? newop1 = GEN_INT (bits - INTVAL (op1));
> ? ? else if (targetm.shift_truncation_mask (mode) == bits - 1)
> ? newop1 = negate_rtx (mode, op1);
> ? ? else
> ? newop1 = expand_binop (mode, sub_optab,
> ? ? ? ? ? ? ? ? ?GEN_INT (bits), op1,
> ? ? ? ? ? ? ? ? ?NULL_RTX, unsignedp, OPTAB_DIRECT);
>