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];
}
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
>>>
>
>
>
