On Wed, May 19, 2021 at 9:05 PM H.J. Lu <hjl.to...@gmail.com> wrote:
>
> On Wed, May 19, 2021 at 6:27 AM Bernd Edlinger
> <bernd.edlin...@hotmail.de> wrote:
> >
> > On 5/19/21 3:22 PM, H.J. Lu wrote:
> > > On Wed, May 19, 2021 at 2:33 AM Richard Biener
> > > <richard.guent...@gmail.com> wrote:
> > >>
> > >> On Tue, May 18, 2021 at 9:16 PM H.J. Lu <hjl.to...@gmail.com> wrote:
> > >>>
> > >>> When expanding a constant constructor, don't call expand_constructor if
> > >>> it is more efficient to load the data from the memory via move by
> > >>> pieces.
> > >>>
> > >>> gcc/
> > >>>
> > >>> PR middle-end/90773
> > >>> * expr.c (expand_expr_real_1): Don't call expand_constructor if
> > >>> it is more efficient to load the data from the memory.
> > >>>
> > >>> gcc/testsuite/
> > >>>
> > >>> PR middle-end/90773
> > >>> * gcc.target/i386/pr90773-24.c: New test.
> > >>> * gcc.target/i386/pr90773-25.c: Likewise.
> > >>> ---
> > >>> gcc/expr.c | 10 ++++++++++
> > >>> gcc/testsuite/gcc.target/i386/pr90773-24.c | 22 ++++++++++++++++++++++
> > >>> gcc/testsuite/gcc.target/i386/pr90773-25.c | 20 ++++++++++++++++++++
> > >>> 3 files changed, 52 insertions(+)
> > >>> create mode 100644 gcc/testsuite/gcc.target/i386/pr90773-24.c
> > >>> create mode 100644 gcc/testsuite/gcc.target/i386/pr90773-25.c
> > >>>
> > >>> diff --git a/gcc/expr.c b/gcc/expr.c
> > >>> index d09ee42e262..80e01ea1cbe 100644
> > >>> --- a/gcc/expr.c
> > >>> +++ b/gcc/expr.c
> > >>> @@ -10886,6 +10886,16 @@ expand_expr_real_1 (tree exp, rtx target,
> > >>> machine_mode tmode,
> > >>> unsigned HOST_WIDE_INT ix;
> > >>> tree field, value;
> > >>>
> > >>> + /* Check if it is more efficient to load the data from
> > >>> + the memory directly. FIXME: How many stores do we
> > >>> + need here if not moved by pieces? */
> > >>> + unsigned HOST_WIDE_INT bytes
> > >>> + = tree_to_uhwi (TYPE_SIZE_UNIT (type));
> > >>
> > >> that's prone to fail - it could be a VLA.
> > >
> > > What do you mean by fail? Is it ICE or missed optimization?
> > > Do you have a testcase?
> > >
> >
> > I think for a VLA the TYPE_SIZE_UNIT may be unknown (NULL), or something
> > like "x".
> >
> > for instance something like
> >
> > int test (int x)
> > {
> > int vla[x];
> >
> > vla[x-1] = 0;
> > return vla[x-1];
> > }
>
> My patch changes the CONSTRUCTOR code path. I couldn't find a CONSTRUCTOR
> testcase with VLA.
nevertheless it doens't hurt to check tree_fits_uhwi (TYPE_SIZE_UNIT (type)),
there's also int_size_in_bytes () returning a signed HOST_WIDE_INT and -1
on "failure" that would work well in your case.
> >
> > Bernd.
> >
> > >>
> > >>> + if ((bytes / UNITS_PER_WORD) > 2
> > >>> + && MOVE_MAX_PIECES > UNITS_PER_WORD
> > >>> + && can_move_by_pieces (bytes, TYPE_ALIGN (type)))
> > >>> + goto normal_inner_ref;
> > >>> +
> > >>
> > >> It looks like you're concerned about aggregate copies but this also
> > >> handles
> > >> non-aggregates (which on GIMPLE might already be optimized of course).
> > >
> > > Here I check if we copy more than 2 words and we can move more than
> > > a word in a single instruction.
> > >
> > >> Also you say "if it's cheaper" but I see no cost considerations. How do
> > >> we generally handle immed const vs. load from constant pool costs?
> > >
> > > This trades 2 (update to 8) stores with one load plus one store. Is there
> > > a way to check which one is faster?
> > >
> > >>> FOR_EACH_CONSTRUCTOR_ELT (CONSTRUCTOR_ELTS (init), ix,
> > >>> field, value)
> > >>> if (tree_int_cst_equal (field, index))
> > >>> diff --git a/gcc/testsuite/gcc.target/i386/pr90773-24.c
> > >>> b/gcc/testsuite/gcc.target/i386/pr90773-24.c
> > >>> new file mode 100644
> > >>> index 00000000000..4a4b62533dc
> > >>> --- /dev/null
> > >>> +++ b/gcc/testsuite/gcc.target/i386/pr90773-24.c
> > >>> @@ -0,0 +1,22 @@
> > >>> +/* { dg-do compile } */
> > >>> +/* { dg-options "-O2 -march=x86-64" } */
> > >>> +
> > >>> +struct S
> > >>> +{
> > >>> + long long s1 __attribute__ ((aligned (8)));
> > >>> + unsigned s2, s3, s4, s5, s6, s7, s8, s9, s10, s11, s12, s13, s14;
> > >>> +};
> > >>> +
> > >>> +const struct S array[] = {
> > >>> + { 0, 60, 640, 2112543726, 39682, 48, 16, 33, 10, 96, 2, 0, 0, 4 }
> > >>> +};
> > >>> +
> > >>> +void
> > >>> +foo (struct S *x)
> > >>> +{
> > >>> + x[0] = array[0];
> > >>> +}
> > >>> +/* { dg-final { scan-assembler-times "movups\[\\t \]%xmm\[0-9\]+,
> > >>> \\(%\[\^,\]+\\)" 1 } } */
> > >>> +/* { dg-final { scan-assembler-times "movups\[\\t \]%xmm\[0-9\]+,
> > >>> 16\\(%\[\^,\]+\\)" 1 } } */
> > >>> +/* { dg-final { scan-assembler-times "movups\[\\t \]%xmm\[0-9\]+,
> > >>> 32\\(%\[\^,\]+\\)" 1 } } */
> > >>> +/* { dg-final { scan-assembler-times "movups\[\\t \]%xmm\[0-9\]+,
> > >>> 48\\(%\[\^,\]+\\)" 1 } } */
> > >>> diff --git a/gcc/testsuite/gcc.target/i386/pr90773-25.c
> > >>> b/gcc/testsuite/gcc.target/i386/pr90773-25.c
> > >>> new file mode 100644
> > >>> index 00000000000..2520b670989
> > >>> --- /dev/null
> > >>> +++ b/gcc/testsuite/gcc.target/i386/pr90773-25.c
> > >>> @@ -0,0 +1,20 @@
> > >>> +/* { dg-do compile } */
> > >>> +/* { dg-options "-O2 -march=skylake" } */
> > >>> +
> > >>> +struct S
> > >>> +{
> > >>> + long long s1 __attribute__ ((aligned (8)));
> > >>> + unsigned s2, s3, s4, s5, s6, s7, s8, s9, s10, s11, s12, s13, s14;
> > >>> +};
> > >>> +
> > >>> +const struct S array[] = {
> > >>> + { 0, 60, 640, 2112543726, 39682, 48, 16, 33, 10, 96, 2, 0, 0, 4 }
> > >>> +};
> > >>> +
> > >>> +void
> > >>> +foo (struct S *x)
> > >>> +{
> > >>> + x[0] = array[0];
> > >>> +}
> > >>> +/* { dg-final { scan-assembler-times "vmovdqu\[\\t \]%ymm\[0-9\]+,
> > >>> \\(%\[\^,\]+\\)" 1 } } */
> > >>> +/* { dg-final { scan-assembler-times "vmovdqu\[\\t \]%ymm\[0-9\]+,
> > >>> 32\\(%\[\^,\]+\\)" 1 } } */
> > >>> --
> > >>> 2.31.1
> > >>>
> > >
> > >
> > >
>
>
>
> --
> H.J.
