> Pengxuan Zheng <quic_pzh...@quicinc.com> writes:
> > We can still use SVE's INDEX instruction to construct vectors even if
> > not all elements are constants. For example, { 0, x, 2, 3 } can be
> > constructed by first using "INDEX #0, #1" to generate { 0, 1, 2, 3 },
> > and then set the elements which are non-constants separately.
> >
> > PR target/113328
> >
> > gcc/ChangeLog:
> >
> > * config/aarch64/aarch64.cc (aarch64_expand_vector_init_fallback):
> > Improve part-variable vector generation with SVE's INDEX if
> TARGET_SVE
> > is available.
> >
> > gcc/testsuite/ChangeLog:
> >
> > * gcc.target/aarch64/sve/acle/general/dupq_1.c: Update test to use
> > check-function-bodies.
> > * gcc.target/aarch64/sve/acle/general/dupq_2.c: Likewise.
> > * gcc.target/aarch64/sve/acle/general/dupq_3.c: Likewise.
> > * gcc.target/aarch64/sve/acle/general/dupq_4.c: Likewise.
> > * gcc.target/aarch64/sve/vec_init_4.c: New test.
> > * gcc.target/aarch64/sve/vec_init_5.c: New test.
> >
> > Signed-off-by: Pengxuan Zheng <quic_pzh...@quicinc.com>
> > ---
> > gcc/config/aarch64/aarch64.cc | 81 ++++++++++++++++++-
> > .../aarch64/sve/acle/general/dupq_1.c | 18 ++++-
> > .../aarch64/sve/acle/general/dupq_2.c | 18 ++++-
> > .../aarch64/sve/acle/general/dupq_3.c | 18 ++++-
> > .../aarch64/sve/acle/general/dupq_4.c | 18 ++++-
> > .../gcc.target/aarch64/sve/vec_init_4.c | 47 +++++++++++
> > .../gcc.target/aarch64/sve/vec_init_5.c | 12 +++
> > 7 files changed, 199 insertions(+), 13 deletions(-) create mode
> > 100644 gcc/testsuite/gcc.target/aarch64/sve/vec_init_4.c
> > create mode 100644 gcc/testsuite/gcc.target/aarch64/sve/vec_init_5.c
> >
> > diff --git a/gcc/config/aarch64/aarch64.cc
> > b/gcc/config/aarch64/aarch64.cc index 6b3ca57d0eb..7305a5c6375 100644
> > --- a/gcc/config/aarch64/aarch64.cc
> > +++ b/gcc/config/aarch64/aarch64.cc
> > @@ -23942,12 +23942,91 @@ aarch64_expand_vector_init_fallback (rtx
> target, rtx vals)
> > if (n_var != n_elts)
> > {
> > rtx copy = copy_rtx (vals);
> > + bool is_index_seq = false;
> > +
> > + /* If at least half of the elements of the vector are constants and
> > all
> > + these constant elements form a linear sequence of the form { B, B +
> S,
> > + B + 2 * S, B + 3 * S, ... }, we can generate the vector with SVE's
> > + INDEX instruction if SVE is available and then set the elements which
> > + are not constant separately. More precisely, each constant element I
> > + has to be B + I * S where B and S must be valid immediate operand
> for
> > + an SVE INDEX instruction.
> > +
> > + For example, { X, 1, 2, 3} is a vector satisfying these conditions and
> > + we can generate a vector of all constants (i.e., { 0, 1, 2, 3 }) first
> > + and then set the first element of the vector to X. */
> > +
> > + if (TARGET_SVE && GET_MODE_CLASS (mode) == MODE_VECTOR_INT
> > + && n_var <= n_elts / 2)
> > + {
> > + int const_idx = -1;
> > + HOST_WIDE_INT const_val = 0;
> > + int base = 16;
> > + int step = 16;
> > +
> > + for (int i = 0; i < n_elts; ++i)
> > + {
> > + rtx x = XVECEXP (vals, 0, i);
> > +
> > + if (!CONST_INT_P (x))
> > + continue;
> > +
> > + if (const_idx == -1)
> > + {
> > + const_idx = i;
> > + const_val = INTVAL (x);
> > + }
> > + else
> > + {
> > + if ((INTVAL (x) - const_val) % (i - const_idx) == 0)
> > + {
> > + HOST_WIDE_INT s
> > + = (INTVAL (x) - const_val) / (i - const_idx);
> > + if (s >= -16 && s <= 15)
> > + {
> > + int b = const_val - s * const_idx;
> > + if (b >= -16 && b <= 15)
> > + {
> > + base = b;
> > + step = s;
> > + }
> > + }
> > + }
> > + break;
> > + }
> > + }
> > +
> > + if (base != 16
> > + && (!CONST_INT_P (v0)
> > + || (CONST_INT_P (v0) && INTVAL (v0) == base)))
> > + {
> > + if (!CONST_INT_P (v0))
> > + XVECEXP (copy, 0, 0) = GEN_INT (base);
> > +
> > + is_index_seq = true;
> > + for (int i = 1; i < n_elts; ++i)
> > + {
> > + rtx x = XVECEXP (copy, 0, i);
> > +
> > + if (CONST_INT_P (x))
> > + {
> > + if (INTVAL (x) != base + i * step)
> > + {
> > + is_index_seq = false;
> > + break;
> > + }
> > + }
> > + else
> > + XVECEXP (copy, 0, i) = GEN_INT (base + i * step);
> > + }
> > + }
> > + }
>
> This seems a bit more complex than I was hoping for, although the complexity
> is probably justified.
>
> Seeing how awkard it is to do this using current interfaces, I think I'd
> instead
> prefer to do something that I'd been vaguely hoping to do for a while: extend
> vector-builder.h to accept wildcard/don't care values.
> finalize () could then replace the wildcards with whatever gives the "nicest"
> encoding.
>
> That's also going to be relatively complex, but I think it'd be more general,
> and
> might help with the existing vec_init code as well.
> It would also be a step towards optimising -1 indices for
> __builtin_shufflevector. It might be a few weeks before I can post something
> though.
No problem, Richard.
I am also curious to see what this alternative implementation looks like.
Please kindly keep me posted when your patch is ready. Thank you!
>
> Pushing 1/2 without 2/2 has meant that the dupq tests will fail in the
> meantime, but that's ok. In general, though, it's better not to push
> individual
> patches from a series unless they've been tested in isolation and are known
> to give clean test results.
In fact, the dupq tests were not affected. Patch 1/2 already adjusted the
"scan-assembler" checks of the dupq tests based on the output of 1/2 alone.
Patch 2/2 just replaces the "scan-assembler" checks with
"check-function-bodies." So, the dupq tests still pass without 2/2.
Thanks,
Pengxuan
>
> Thanks,
> Richard
