[PATCH] Improve gimplification of constructors with RANGE_EXPRs (PR c++/82294, PR c++/87436)
Richard Biener
rguenther@suse.de
Fri Dec 14 11:22:00 GMT 2018
On Fri, 14 Dec 2018, Jakub Jelinek wrote:
> On Fri, Dec 14, 2018 at 10:40:19AM +0100, Richard Biener wrote:
> > This looks OK to me - the only comment I have is on the two magic
> > constants (64 and 8) which are used twice in the patch. Can you
> > either see to hoist the common condition into sth like
> >
> > bool prefer_loop_initializer_p = ...
> >
> > or add #defines for those constants? I suppose the hoisting
> > might be tricky as int_size_in_bytes can return -1 and the
> > workarounds are different in both places right now (maybe that's
> > a bug as well...). OTOH using (unsigned)int_size_in_bytes
> > looks reasonable in general.
>
> So like this?
Yes.
Thanks,
Richard.
> Still need to wait for the FE patch if I want to commit the testcases, those
> depend on both patches.
> I've added size32plus effective target to the larger test, as 384MB is too
> much for 16 or 20 bit address targets.
> And, I'll gather statistics on how often this makes a difference during
> gimplification during my next bootstraps/regtests.
>
> 2018-12-14 Jakub Jelinek <jakub@redhat.com>
>
> PR c++/82294
> PR c++/87436
> * expr.h (categorize_ctor_elements): Add p_unique_nz_elts argument.
> * expr.c (categorize_ctor_elements_1): Likewise. Compute it like
> p_nz_elts, except don't multiply it by mult. Adjust recursive call.
> Fix up COMPLEX_CST handling.
> (categorize_ctor_elements): Add p_unique_nz_elts argument, initialize
> it and pass it through to categorize_ctor_elements_1.
> (mostly_zeros_p, all_zeros_p): Adjust categorize_ctor_elements callers.
> * gimplify.c (gimplify_init_constructor): Likewise. Don't force
> ctor into readonly data section if num_unique_nonzero_elements is
> smaller or equal to 1/8 of num_nonzero_elements and size is >= 64
> bytes.
>
> * g++.dg/tree-ssa/pr82294.C: New test.
> * g++.dg/tree-ssa/pr87436.C: New test.
>
> --- gcc/expr.h.jj 2018-12-13 18:00:10.527301479 +0100
> +++ gcc/expr.h 2018-12-14 11:52:31.941071185 +0100
> @@ -309,7 +309,8 @@ extern bool can_move_by_pieces (unsigned
> extern unsigned HOST_WIDE_INT highest_pow2_factor (const_tree);
>
> extern bool categorize_ctor_elements (const_tree, HOST_WIDE_INT *,
> - HOST_WIDE_INT *, bool *);
> + HOST_WIDE_INT *, HOST_WIDE_INT *,
> + bool *);
>
> extern void expand_operands (tree, tree, rtx, rtx*, rtx*,
> enum expand_modifier);
> --- gcc/expr.c.jj 2018-12-13 18:00:10.426303121 +0100
> +++ gcc/expr.c 2018-12-14 11:52:31.945071118 +0100
> @@ -5945,10 +5945,11 @@ count_type_elements (const_tree type, bo
>
> static bool
> categorize_ctor_elements_1 (const_tree ctor, HOST_WIDE_INT *p_nz_elts,
> + HOST_WIDE_INT *p_unique_nz_elts,
> HOST_WIDE_INT *p_init_elts, bool *p_complete)
> {
> unsigned HOST_WIDE_INT idx;
> - HOST_WIDE_INT nz_elts, init_elts, num_fields;
> + HOST_WIDE_INT nz_elts, unique_nz_elts, init_elts, num_fields;
> tree value, purpose, elt_type;
>
> /* Whether CTOR is a valid constant initializer, in accordance with what
> @@ -5958,6 +5959,7 @@ categorize_ctor_elements_1 (const_tree c
> bool const_p = const_from_elts_p ? true : TREE_STATIC (ctor);
>
> nz_elts = 0;
> + unique_nz_elts = 0;
> init_elts = 0;
> num_fields = 0;
> elt_type = NULL_TREE;
> @@ -5982,12 +5984,13 @@ categorize_ctor_elements_1 (const_tree c
> {
> case CONSTRUCTOR:
> {
> - HOST_WIDE_INT nz = 0, ic = 0;
> + HOST_WIDE_INT nz = 0, unz = 0, ic = 0;
>
> - bool const_elt_p = categorize_ctor_elements_1 (value, &nz, &ic,
> - p_complete);
> + bool const_elt_p = categorize_ctor_elements_1 (value, &nz, &unz,
> + &ic, p_complete);
>
> nz_elts += mult * nz;
> + unique_nz_elts += unz;
> init_elts += mult * ic;
>
> if (const_from_elts_p && const_p)
> @@ -5999,21 +6002,31 @@ categorize_ctor_elements_1 (const_tree c
> case REAL_CST:
> case FIXED_CST:
> if (!initializer_zerop (value))
> - nz_elts += mult;
> + {
> + nz_elts += mult;
> + unique_nz_elts++;
> + }
> init_elts += mult;
> break;
>
> case STRING_CST:
> nz_elts += mult * TREE_STRING_LENGTH (value);
> + unique_nz_elts += TREE_STRING_LENGTH (value);
> init_elts += mult * TREE_STRING_LENGTH (value);
> break;
>
> case COMPLEX_CST:
> if (!initializer_zerop (TREE_REALPART (value)))
> - nz_elts += mult;
> + {
> + nz_elts += mult;
> + unique_nz_elts++;
> + }
> if (!initializer_zerop (TREE_IMAGPART (value)))
> - nz_elts += mult;
> - init_elts += mult;
> + {
> + nz_elts += mult;
> + unique_nz_elts++;
> + }
> + init_elts += 2 * mult;
> break;
>
> case VECTOR_CST:
> @@ -6025,7 +6038,10 @@ categorize_ctor_elements_1 (const_tree c
> {
> tree v = VECTOR_CST_ELT (value, i);
> if (!initializer_zerop (v))
> - nz_elts += mult;
> + {
> + nz_elts += mult;
> + unique_nz_elts++;
> + }
> init_elts += mult;
> }
> }
> @@ -6035,6 +6051,7 @@ categorize_ctor_elements_1 (const_tree c
> {
> HOST_WIDE_INT tc = count_type_elements (elt_type, false);
> nz_elts += mult * tc;
> + unique_nz_elts += tc;
> init_elts += mult * tc;
>
> if (const_from_elts_p && const_p)
> @@ -6054,6 +6071,7 @@ categorize_ctor_elements_1 (const_tree c
> *p_complete = false;
>
> *p_nz_elts += nz_elts;
> + *p_unique_nz_elts += unique_nz_elts;
> *p_init_elts += init_elts;
>
> return const_p;
> @@ -6062,6 +6080,11 @@ categorize_ctor_elements_1 (const_tree c
> /* Examine CTOR to discover:
> * how many scalar fields are set to nonzero values,
> and place it in *P_NZ_ELTS;
> + * the same, but counting RANGE_EXPRs as multiplier of 1 instead of
> + high - low + 1 (this can be useful for callers to determine ctors
> + that could be cheaply initialized with - perhaps nested - loops
> + compared to copied from huge read-only data),
> + and place it in *P_UNIQUE_NZ_ELTS;
> * how many scalar fields in total are in CTOR,
> and place it in *P_ELT_COUNT.
> * whether the constructor is complete -- in the sense that every
> @@ -6073,13 +6096,16 @@ categorize_ctor_elements_1 (const_tree c
>
> bool
> categorize_ctor_elements (const_tree ctor, HOST_WIDE_INT *p_nz_elts,
> + HOST_WIDE_INT *p_unique_nz_elts,
> HOST_WIDE_INT *p_init_elts, bool *p_complete)
> {
> *p_nz_elts = 0;
> + *p_unique_nz_elts = 0;
> *p_init_elts = 0;
> *p_complete = true;
>
> - return categorize_ctor_elements_1 (ctor, p_nz_elts, p_init_elts, p_complete);
> + return categorize_ctor_elements_1 (ctor, p_nz_elts, p_unique_nz_elts,
> + p_init_elts, p_complete);
> }
>
> /* TYPE is initialized by a constructor with NUM_ELTS elements, the last
> @@ -6110,17 +6136,18 @@ complete_ctor_at_level_p (const_tree typ
> return count_type_elements (type, true) == num_elts;
> }
>
> -/* Return 1 if EXP contains mostly (3/4) zeros. */
> +/* Return 1 if EXP contains mostly (3/4) zeros. */
>
> static int
> mostly_zeros_p (const_tree exp)
> {
> if (TREE_CODE (exp) == CONSTRUCTOR)
> {
> - HOST_WIDE_INT nz_elts, init_elts;
> + HOST_WIDE_INT nz_elts, unz_elts, init_elts;
> bool complete_p;
>
> - categorize_ctor_elements (exp, &nz_elts, &init_elts, &complete_p);
> + categorize_ctor_elements (exp, &nz_elts, &unz_elts, &init_elts,
> + &complete_p);
> return !complete_p || nz_elts < init_elts / 4;
> }
>
> @@ -6134,10 +6161,11 @@ all_zeros_p (const_tree exp)
> {
> if (TREE_CODE (exp) == CONSTRUCTOR)
> {
> - HOST_WIDE_INT nz_elts, init_elts;
> + HOST_WIDE_INT nz_elts, unz_elts, init_elts;
> bool complete_p;
>
> - categorize_ctor_elements (exp, &nz_elts, &init_elts, &complete_p);
> + categorize_ctor_elements (exp, &nz_elts, &unz_elts, &init_elts,
> + &complete_p);
> return nz_elts == 0;
> }
>
> --- gcc/gimplify.c.jj 2018-12-13 18:00:10.597300341 +0100
> +++ gcc/gimplify.c 2018-12-14 12:01:17.491402703 +0100
> @@ -4778,7 +4778,15 @@ gimplify_init_constructor (tree *expr_p,
> {
> struct gimplify_init_ctor_preeval_data preeval_data;
> HOST_WIDE_INT num_ctor_elements, num_nonzero_elements;
> + HOST_WIDE_INT num_unique_nonzero_elements;
> bool cleared, complete_p, valid_const_initializer;
> + /* Use readonly data for initializers of this or smaller size
> + regardless of the num_nonzero_elements / num_unique_nonzero_elements
> + ratio. */
> + const HOST_WIDE_INT min_unique_size = 64;
> + /* If num_nonzero_elements / num_unique_nonzero_elements ratio
> + is smaller than this, use readonly data. */
> + const int unique_nonzero_ratio = 8;
>
> /* Aggregate types must lower constructors to initialization of
> individual elements. The exception is that a CONSTRUCTOR node
> @@ -4795,6 +4803,7 @@ gimplify_init_constructor (tree *expr_p,
> can only do so if it known to be a valid constant initializer. */
> valid_const_initializer
> = categorize_ctor_elements (ctor, &num_nonzero_elements,
> + &num_unique_nonzero_elements,
> &num_ctor_elements, &complete_p);
>
> /* If a const aggregate variable is being initialized, then it
> @@ -4803,7 +4812,15 @@ gimplify_init_constructor (tree *expr_p,
> && num_nonzero_elements > 1
> && TREE_READONLY (object)
> && VAR_P (object)
> - && (flag_merge_constants >= 2 || !TREE_ADDRESSABLE (object)))
> + && (flag_merge_constants >= 2 || !TREE_ADDRESSABLE (object))
> + /* For ctors that have many repeated nonzero elements
> + represented through RANGE_EXPRs, prefer initializing
> + those through runtime loops over copies of large amounts
> + of data from readonly data section. */
> + && (num_unique_nonzero_elements
> + > num_nonzero_elements / unique_nonzero_ratio
> + || ((unsigned HOST_WIDE_INT) int_size_in_bytes (type)
> + <= (unsigned HOST_WIDE_INT) min_unique_size)))
> {
> if (notify_temp_creation)
> return GS_ERROR;
> @@ -4896,6 +4913,13 @@ gimplify_init_constructor (tree *expr_p,
> is so large as to make individual moves inefficient. */
> if (size > 0
> && num_nonzero_elements > 1
> + /* For ctors that have many repeated nonzero elements
> + represented through RANGE_EXPRs, prefer initializing
> + those through runtime loops over copies of large amounts
> + of data from readonly data section. */
> + && (num_unique_nonzero_elements
> + > num_nonzero_elements / unique_nonzero_ratio
> + || size < min_unique_size)
> && (size < num_nonzero_elements
> || !can_move_by_pieces (size, align)))
> {
> --- gcc/testsuite/g++.dg/tree-ssa/pr82294.C.jj 2018-12-14 11:52:31.949071052 +0100
> +++ gcc/testsuite/g++.dg/tree-ssa/pr82294.C 2018-12-14 11:52:31.949071052 +0100
> @@ -0,0 +1,13 @@
> +// PR c++/82294
> +// { dg-do compile { target c++11 } }
> +// { dg-options "-O2 -fdump-tree-gimple" }
> +
> +// Verify we don't "optimize" the ctor as copying a 1KB .rodata
> +// object into the variable. It is better to initialize it through
> +// a loop.
> +// { dg-final { scan-tree-dump-not "this->arr = " "gimple" } }
> +
> +struct S { int x; explicit constexpr S (); };
> +constexpr S::S () : x{7} {}
> +struct T { S arr[256]; explicit T (); };
> +T::T () {}
> --- gcc/testsuite/g++.dg/tree-ssa/pr87436.C.jj 2018-12-14 11:52:31.949071052 +0100
> +++ gcc/testsuite/g++.dg/tree-ssa/pr87436.C 2018-12-14 11:52:31.949071052 +0100
> @@ -0,0 +1,25 @@
> +// PR c++/87436
> +// { dg-do compile { target { c++11 && size32plus } } }
> +// { dg-options "-O2 -fdump-tree-gimple" }
> +
> +// Verify we don't "optimize" the ctor as copying a 384MB .rodata
> +// object into the variable. It is better to initialize it through
> +// two nested loops.
> +// { dg-final { scan-tree-dump-not "this->arr = " "gimple" } }
> +
> +struct S {
> + int a = -1;
> + short b = 3;
> + int x = 0;
> + int y = 1;
> + int z = 42;
> + float f = 0.123f;
> +};
> +
> +struct T { S arr[4096][4096]; };
> +
> +T *
> +foo ()
> +{
> + return new T;
> +}
>
>
> Jakub
>
>
--
Richard Biener <rguenther@suse.de>
SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nuernberg)
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