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.
>
> 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.
