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? > > > + 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.