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?
> + 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" } } */
>
>
>
