On 25/11/2024 20:08, Christophe Lyon wrote:
> In this PR, we have to handle a case where MVE predicates are supplied
> as a const_int, where individual predicates have illegal boolean
> values (such as 0xc for a 4-bit boolean predicate). To avoid the ICE,
> fix the constant (any non-zero value is converted to all 1s) and emit
> a warning.
>
> On MVE, V8BI and V4BI multi-bit masks are interpreted byte-by-byte at
> instruction level, but end-users should describe lanes rather than
> bytes (so all bytes of a true-predicated lane should be '1'), see
> https://developer.arm.com/documentation/101028/0012/14--M-profile-Vector-Extension--MVE--intrinsics.
>
> Since gen_lowpart can ICE on a subreg, we force predicates in a subreg
> into a reg, after removing subreg of the same size as the target
> (HImode) which would be made redundant by gen_lowpart and confuse the
> DLSTP optimization.
>
> 2024-11-20 Christophe Lyon <[email protected]>
> Jakub Jelinek <[email protected]>
>
> PR target/114801
> gcc/
> * config/arm/arm-mve-builtins.cc
> (function_expander::add_input_operand): Handle CONST_INT
> predicates.
>
> gcc/testsuite/
> * gcc.target/arm/mve/pr108443.c: Update predicate constant.
> * gcc.target/arm/mve/pr114801.c: New test.
> ---
> gcc/config/arm/arm-mve-builtins.cc | 37 ++++++++++++++++++-
> gcc/testsuite/gcc.target/arm/mve/pr108443.c | 4 +--
> gcc/testsuite/gcc.target/arm/mve/pr114801.c | 39 +++++++++++++++++++++
> 3 files changed, 77 insertions(+), 3 deletions(-)
> create mode 100644 gcc/testsuite/gcc.target/arm/mve/pr114801.c
>
> diff --git a/gcc/config/arm/arm-mve-builtins.cc
> b/gcc/config/arm/arm-mve-builtins.cc
> index 255aed25600..5ff32ce06b7 100644
> --- a/gcc/config/arm/arm-mve-builtins.cc
> +++ b/gcc/config/arm/arm-mve-builtins.cc
> @@ -2352,7 +2352,42 @@ function_expander::add_input_operand (insn_code icode,
> rtx x)
> mode = GET_MODE (x);
> }
> else if (VALID_MVE_PRED_MODE (mode))
> - x = gen_lowpart (mode, x);
> + {
> + if (CONST_INT_P (x) && (mode == V8BImode || mode == V4BImode))
> + {
> + /* In V8BI or V4BI each element has 2 or 4 bits, if those bits aren't
> + all the same, gen_lowpart might ICE. Canonicalize all the 2 or 4
> + bits to all ones if any of them is non-zero. V8BI and V4BI
> + multi-bit masks are interpreted byte-by-byte at instruction level,
> + but such constants should describe lanes, rather than bytes. See
> +
> https://developer.arm.com/documentation/101028/0012/14--M-profile-Vector-Extension--MVE--intrinsics.
> */
Apart from being an overly long line, deep links like this are generally not
very stable. I suggest we just say something like "See the section on MVE
intrinsics in the Arm ACLE specification".
> + unsigned HOST_WIDE_INT xi = UINTVAL (x);
> + xi |= ((xi & 0x5555) << 1) | ((xi & 0xaaaa) >> 1);
> + if (mode == V4BImode)
> + xi |= ((xi & 0x3333) << 2) | ((xi & 0xcccc) >> 2);
> + if (xi != UINTVAL (x))
> + inform (location, "constant predicate argument %d (%wx) does"
> + " not map to %d lane numbers, converted to %wx",
> + opno, UINTVAL (x) & 0xffff, mode == V8BImode ? 8 : 4,
> + xi & 0xffff);
I think this should be a warning (so that werror can work with it). Otherwise
such messages can't be faulted.
> +
> + x = gen_int_mode (xi, HImode);
> + }
> + else if (SUBREG_P (x))
> + {
> + /* Already of the right size, drop the subreg which will be made
> + redundant by gen_lowpart below. */
> + if (GET_MODE_SIZE (GET_MODE (x)) == GET_MODE_SIZE (HImode)
> + || SUBREG_BYTE (x) == 0)
> + x = SUBREG_REG (x);
> +
> + /* gen_lowpart on a SUBREG can ICE. */
> + if (gen_lowpart_common (mode, x) == 0)
> + x = force_reg (GET_MODE (x), x);
> + }
> +
> + x = gen_lowpart (mode, x);
I wonder if this is overly complex. Wouldn't it be better to just write here:
else if (!REG_P (x))
x = force_reg (GET_MODE (x), x);
and then let the optimizers clean things up?
R.
> + }
>
> m_ops.safe_grow (m_ops.length () + 1, true);
> create_input_operand (&m_ops.last (), x, mode);
> diff --git a/gcc/testsuite/gcc.target/arm/mve/pr108443.c
> b/gcc/testsuite/gcc.target/arm/mve/pr108443.c
> index c5fbfa4a1bb..0c0e2dd6eb8 100644
> --- a/gcc/testsuite/gcc.target/arm/mve/pr108443.c
> +++ b/gcc/testsuite/gcc.target/arm/mve/pr108443.c
> @@ -7,8 +7,8 @@
> void
> __attribute__ ((noipa)) partial_write_cst (uint32_t *a, uint32x4_t v)
> {
> - vstrwq_p_u32 (a, v, 0x00CC);
> + vstrwq_p_u32 (a, v, 0x00FF);
> }
>
> -/* { dg-final { scan-assembler {mov\tr[0-9]+, #204} } } */
> +/* { dg-final { scan-assembler {mov\tr[0-9]+, #255} } } */
>
> diff --git a/gcc/testsuite/gcc.target/arm/mve/pr114801.c
> b/gcc/testsuite/gcc.target/arm/mve/pr114801.c
> new file mode 100644
> index 00000000000..d051e309d0b
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/arm/mve/pr114801.c
> @@ -0,0 +1,39 @@
> +/* { dg-do compile } */
> +/* { dg-require-effective-target arm_v8_1m_mve_ok } */
> +/* { dg-options "-O2" } */
> +/* { dg-add-options arm_v8_1m_mve } */
> +/* { dg-final { check-function-bodies "**" "" "" } } */
> +
> +#include <arm_mve.h>
> +
> +/*
> +** test_32:
> +**...
> +** mov r[0-9]+, #65295 @ movhi
> +**...
> +*/
> +uint32x4_t test_32() {
> + /* V4BI predicate converted to 0xff0f. */
> + return vdupq_m_n_u32(vdupq_n_u32(0xffffffff), 0, 0x4f02); /* { dg-note
> {constant predicate argument 3 \(0x4f02\) does not map to 4 lane numbers,
> converted to 0xff0f} } */
> +}
> +
> +/*
> +** test_16:
> +**...
> +** mov r[0-9]+, #12339 @ movhi
> +**...
> +*/
> +uint16x8_t test_16() {
> + /* V8BI predicate converted to 0x3033. */
> + return vdupq_m_n_u16(vdupq_n_u16(0xffff), 0, 0x3021); /* { dg-note
> {constant predicate argument 3 \(0x3021\) does not map to 8 lane numbers,
> converted to 0x3033} } */
> +}
> +
> +/*
> +** test_8:
> +**...
> +** mov r[0-9]+, #23055 @ movhi
> +**...
> +*/
> +uint8x16_t test_8() {
> + return vdupq_m_n_u8(vdupq_n_u8(0xff), 0, 0x5a0f);
> +}
