On Wed, Sep 2, 2015 at 11:14 PM, Bill Schmidt
<wschm...@linux.vnet.ibm.com> wrote:
>
> On Wed, 2015-09-02 at 14:44 +0200, Richard Biener wrote:
>> On Tue, Sep 1, 2015 at 5:53 PM, Bill Schmidt
>> <wschm...@linux.vnet.ibm.com> wrote:
>> > On Tue, 2015-09-01 at 11:01 +0200, Richard Biener wrote:
>> >> On Mon, Aug 31, 2015 at 10:28 PM, Bill Schmidt
>> >> <wschm...@linux.vnet.ibm.com> wrote:
>> >> > Hi,
>> >> >
>> >> > The following simple test fails when attempting to convert a vector
>> >> > shift-by-scalar into a vector shift-by-vector.
>> >> >
>> >> > typedef unsigned char v16ui __attribute__((vector_size(16)));
>> >> >
>> >> > v16ui vslb(v16ui v, unsigned char i)
>> >> > {
>> >> > return v << i;
>> >> > }
>> >> >
>> >> > When this code is gimplified, the shift amount gets expanded to an
>> >> > unsigned int:
>> >> >
>> >> > vslb (v16ui v, unsigned char i)
>> >> > {
>> >> > v16ui D.2300;
>> >> > unsigned int D.2301;
>> >> >
>> >> > D.2301 = (unsigned int) i;
>> >> > D.2300 = v << D.2301;
>> >> > return D.2300;
>> >> > }
>> >> >
>> >> > In expand_binop, the shift-by-scalar is converted into a shift-by-vector
>> >> > using expand_vector_broadcast, which produces the following rtx to be
>> >> > used to initialize a V16QI vector:
>> >> >
>> >> > (parallel:V16QI [
>> >> > (subreg/s/v:SI (reg:DI 155) 0)
>> >> > (subreg/s/v:SI (reg:DI 155) 0)
>> >> > (subreg/s/v:SI (reg:DI 155) 0)
>> >> > (subreg/s/v:SI (reg:DI 155) 0)
>> >> > (subreg/s/v:SI (reg:DI 155) 0)
>> >> > (subreg/s/v:SI (reg:DI 155) 0)
>> >> > (subreg/s/v:SI (reg:DI 155) 0)
>> >> > (subreg/s/v:SI (reg:DI 155) 0)
>> >> > (subreg/s/v:SI (reg:DI 155) 0)
>> >> > (subreg/s/v:SI (reg:DI 155) 0)
>> >> > (subreg/s/v:SI (reg:DI 155) 0)
>> >> > (subreg/s/v:SI (reg:DI 155) 0)
>> >> > (subreg/s/v:SI (reg:DI 155) 0)
>> >> > (subreg/s/v:SI (reg:DI 155) 0)
>> >> > (subreg/s/v:SI (reg:DI 155) 0)
>> >> > (subreg/s/v:SI (reg:DI 155) 0)
>> >> > ])
>> >> >
>> >> > The back end eventually chokes trying to generate a copy of the SImode
>> >> > expression into a QImode memory slot.
>> >> >
>> >> > This patch fixes this problem by ensuring that the shift amount is
>> >> > truncated to the inner mode of the vector when necessary. I've added a
>> >> > test case verifying correct PowerPC code generation in this case.
>> >> >
>> >> > Bootstrapped and tested on powerpc64le-unknown-linux-gnu with no
>> >> > regressions. Is this ok for trunk?
>> >> >
>> >> > Thanks,
>> >> > Bill
>> >> >
>> >> >
>> >> > [gcc]
>> >> >
>> >> > 2015-08-31 Bill Schmidt <wschm...@linux.vnet.ibm.com>
>> >> >
>> >> > * optabs.c (expand_binop): Don't create a broadcast vector with
>> >> > a
>> >> > source element wider than the inner mode.
>> >> >
>> >> > [gcc/testsuite]
>> >> >
>> >> > 2015-08-31 Bill Schmidt <wschm...@linux.vnet.ibm.com>
>> >> >
>> >> > * gcc.target/powerpc/vec-shift.c: New test.
>> >> >
>> >> >
>> >> > Index: gcc/optabs.c
>> >> > ===================================================================
>> >> > --- gcc/optabs.c (revision 227353)
>> >> > +++ gcc/optabs.c (working copy)
>> >> > @@ -1608,6 +1608,13 @@ expand_binop (machine_mode mode, optab binoptab,
>> >> > r
>> >> >
>> >> > if (otheroptab && optab_handler (otheroptab, mode) !=
>> >> > CODE_FOR_nothing)
>> >> > {
>> >> > + /* The scalar may have been extended to be too wide. Truncate
>> >> > + it back to the proper size to fit in the broadcast vector.
>> >> > */
>> >> > + machine_mode inner_mode = GET_MODE_INNER (mode);
>> >> > + if (GET_MODE_BITSIZE (inner_mode)
>> >> > + < GET_MODE_BITSIZE (GET_MODE (op1)))
>> >>
>> >> Does that work for modeless constants? Btw, what do other targets do
>> >> here? Do they
>> >> also choke or do they cope with the wide operand?
>> >
>> > Good question. This works by serendipity more than by design. Because
>> > a constant has a mode of VOIDmode, its bitsize is 0 and the TRUNCATE
>> > won't be generated. It would be better for me to put in an explicit
>> > check for CONST_INT rather than relying on this, though. I'll fix that.
>> >
>> > I am not sure what other targets do here; I can check. However, do you
>> > think that's relevant? I'm concerned that
>> >
>> > (parallel:V16QI [
>> > (subreg/s/v:SI (reg:DI 155) 0)
>> > (subreg/s/v:SI (reg:DI 155) 0)
>> > (subreg/s/v:SI (reg:DI 155) 0)
>> > (subreg/s/v:SI (reg:DI 155) 0)
>> > (subreg/s/v:SI (reg:DI 155) 0)
>> > (subreg/s/v:SI (reg:DI 155) 0)
>> > (subreg/s/v:SI (reg:DI 155) 0)
>> > (subreg/s/v:SI (reg:DI 155) 0)
>> > (subreg/s/v:SI (reg:DI 155) 0)
>> > (subreg/s/v:SI (reg:DI 155) 0)
>> > (subreg/s/v:SI (reg:DI 155) 0)
>> > (subreg/s/v:SI (reg:DI 155) 0)
>> > (subreg/s/v:SI (reg:DI 155) 0)
>> > (subreg/s/v:SI (reg:DI 155) 0)
>> > (subreg/s/v:SI (reg:DI 155) 0)
>> > (subreg/s/v:SI (reg:DI 155) 0)
>> > ])
>> >
>> > is a nonsensical expression and shouldn't be produced by common code, in
>> > my view. It seems best to make this explicitly correct. Please let me
>> > know if that's off-base.
>>
>> No, the above indeed looks fishy though other backends vec_init_optab might
>> have just handle it fine.
>>
>> OTOH if a conversion is required it would be nice to CSE it, thus
>> force the result to a register (not sure if the targets handle invalid
>> RTL sharing in vec_init_optab).
>
> Agreed. I've fixed the modeless constant issue and added a force_reg on
> the conversion. New patch below, bootstrapped and tested on
> powerpc64le-unknown-linux-gnu with no regressions. Is this version ok?
Looks good to me.
Thanks,
Richard.
> Thanks!
> Bill
>
>>
>> > Thanks,
>> > Bill
>> >
>> >>
>> >> > + op1 = simplify_gen_unary (TRUNCATE, inner_mode, op1,
>> >> > + GET_MODE (op1));
>> >> > rtx vop1 = expand_vector_broadcast (mode, op1);
>> >> > if (vop1)
>> >> > {
>> >> > Index: gcc/testsuite/gcc.target/powerpc/vec-shift.c
>> >> > ===================================================================
>> >> > --- gcc/testsuite/gcc.target/powerpc/vec-shift.c (revision 0)
>> >> > +++ gcc/testsuite/gcc.target/powerpc/vec-shift.c (working copy)
>> >> > @@ -0,0 +1,20 @@
>> >> > +/* { dg-do compile { target { powerpc*-*-* } } } */
>> >> > +/* { dg-require-effective-target powerpc_altivec_ok } */
>> >> > +/* { dg-skip-if "" { powerpc*-*-darwin* } { "*" } { "" } } */
>> >> > +/* { dg-skip-if "do not override -mcpu" { powerpc*-*-* } { "-mcpu=*" }
>> >> > { "-mcpu=power7" } } */
>> >> > +/* { dg-options "-mcpu=power7 -O2" } */
>> >> > +
>> >> > +/* This used to ICE. During gimplification, "i" is widened to an
>> >> > unsigned
>> >> > + int. We used to fail at expand time as we tried to cram an SImode
>> >> > item
>> >> > + into a QImode memory slot. This has been fixed to properly
>> >> > truncate the
>> >> > + shift amount when splatting it into a vector. */
>> >> > +
>> >> > +typedef unsigned char v16ui __attribute__((vector_size(16)));
>> >> > +
>> >> > +v16ui vslb(v16ui v, unsigned char i)
>> >> > +{
>> >> > + return v << i;
>> >> > +}
>> >> > +
>> >> > +/* { dg-final { scan-assembler "vspltb" } } */
>> >> > +/* { dg-final { scan-assembler "vslb" } } */
>> >> >
>
>
> New patch below:
>
> [gcc]
>
> 2015-09-02 Bill Schmidt <wschm...@linux.vnet.ibm.com>
>
> * optabs.c (expand_binop): Don't create a broadcast vector with a
> source element wider than the inner mode.
>
> [gcc/testsuite]
>
> 2015-09-02 Bill Schmidt <wschm...@linux.vnet.ibm.com>
>
> * gcc.target/powerpc/vec-shift.c: New test.
>
>
> Index: gcc/optabs.c
> ===================================================================
> --- gcc/optabs.c (revision 227416)
> +++ gcc/optabs.c (working copy)
> @@ -1608,6 +1608,15 @@ expand_binop (machine_mode mode, optab binoptab, r
>
> if (otheroptab && optab_handler (otheroptab, mode) != CODE_FOR_nothing)
> {
> + /* The scalar may have been extended to be too wide. Truncate
> + it back to the proper size to fit in the broadcast vector. */
> + machine_mode inner_mode = GET_MODE_INNER (mode);
> + if (!CONST_INT_P (op1)
> + && (GET_MODE_BITSIZE (inner_mode)
> + < GET_MODE_BITSIZE (GET_MODE (op1))))
> + op1 = force_reg (inner_mode,
> + simplify_gen_unary (TRUNCATE, inner_mode, op1,
> + GET_MODE (op1)));
> rtx vop1 = expand_vector_broadcast (mode, op1);
> if (vop1)
> {
> Index: gcc/testsuite/gcc.target/powerpc/vec-shift.c
> ===================================================================
> --- gcc/testsuite/gcc.target/powerpc/vec-shift.c (revision 0)
> +++ gcc/testsuite/gcc.target/powerpc/vec-shift.c (working copy)
> @@ -0,0 +1,20 @@
> +/* { dg-do compile { target { powerpc*-*-* } } } */
> +/* { dg-require-effective-target powerpc_altivec_ok } */
> +/* { dg-skip-if "" { powerpc*-*-darwin* } { "*" } { "" } } */
> +/* { dg-skip-if "do not override -mcpu" { powerpc*-*-* } { "-mcpu=*" } {
> "-mcpu=power7" } } */
> +/* { dg-options "-mcpu=power7 -O2" } */
> +
> +/* This used to ICE. During gimplification, "i" is widened to an unsigned
> + int. We used to fail at expand time as we tried to cram an SImode item
> + into a QImode memory slot. This has been fixed to properly truncate the
> + shift amount when splatting it into a vector. */
> +
> +typedef unsigned char v16ui __attribute__((vector_size(16)));
> +
> +v16ui vslb(v16ui v, unsigned char i)
> +{
> + return v << i;
> +}
> +
> +/* { dg-final { scan-assembler "vspltb" } } */
> +/* { dg-final { scan-assembler "vslb" } } */
>
>
>
>
