On Thu, 6 Dec 2018, Jakub Jelinek wrote:
> Hi!
>
> This is my proposal for fixing this PR, just a heuristics when optimizing
> successive divides might not be a good idea (first testcase), and includes
> Marc's testcases which showed cases where optimizing successive divides is a
> good idea even if the inner divide is not a single use.
>
> Unfortunately match.pd doesn't allow to capture the outermost expression, so
> I can't narrow it even more by checking if the outer divide is in the same
> bb as the modulo.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
+ if (!gimple_in_ssa_p (cfun) || TREE_CODE (inner_div) != SSA_NAME)
+ return false;
I think the latter is always true. The code handles the case of
missing immediate uses by performing the folding which is probably
OK but a general "issue" of using stmt operands or immediate uses
in GIMPLE folding patterns.
I think the patch is OK but I also hope we do not add too many
of these heuristics...
Richard.
> 2018-12-06 Jakub Jelinek <ja...@redhat.com>
>
> PR tree-optimization/85726
> * generic-match-head.c (optimize_successive_divisions_p): New function.
> * gimple-match-head.c (optimize_successive_divisions_p): Likewise.
> * match.pd: Don't combine successive divisions if they aren't exact
> and optimize_successive_divisions_p is false.
>
> * gcc.dg/tree-ssa/pr85726-1.c: New test.
> * gcc.dg/tree-ssa/pr85726-2.c: New test.
> * gcc.dg/tree-ssa/pr85726-3.c: New test.
> * gcc.dg/tree-ssa/pr85726-4.c: New test.
>
> --- gcc/generic-match-head.c.jj 2018-03-28 21:14:28.124743854 +0200
> +++ gcc/generic-match-head.c 2018-12-05 16:07:43.710801347 +0100
> @@ -77,3 +77,12 @@ canonicalize_math_after_vectorization_p
> {
> return false;
> }
> +
> +/* Return true if successive divisions can be optimized.
> + Defer to GIMPLE opts. */
> +
> +static inline bool
> +optimize_successive_divisions_p (tree, tree)
> +{
> + return false;
> +}
> --- gcc/gimple-match-head.c.jj 2018-10-10 10:50:55.812109572 +0200
> +++ gcc/gimple-match-head.c 2018-12-05 16:39:50.358122589 +0100
> @@ -1163,3 +1163,27 @@ optimize_pow_to_exp (tree arg0, tree arg
> return false;
> return true;
> }
> +
> +/* Return true if a division INNER_DIV / DIVISOR where INNER_DIV
> + is another division can be optimized. Don't optimize if INNER_DIV
> + is used in a TRUNC_MOD_EXPR with DIVISOR as second operand. */
> +
> +static bool
> +optimize_successive_divisions_p (tree divisor, tree inner_div)
> +{
> + if (!gimple_in_ssa_p (cfun) || TREE_CODE (inner_div) != SSA_NAME)
> + return false;
> +
> + imm_use_iterator imm_iter;
> + use_operand_p use_p;
> + FOR_EACH_IMM_USE_FAST (use_p, imm_iter, inner_div)
> + {
> + gimple *use_stmt = USE_STMT (use_p);
> + if (!is_gimple_assign (use_stmt)
> + || gimple_assign_rhs_code (use_stmt) != TRUNC_MOD_EXPR
> + || !operand_equal_p (gimple_assign_rhs2 (use_stmt), divisor, 0))
> + continue;
> + return false;
> + }
> + return true;
> +}
> --- gcc/match.pd.jj 2018-11-30 21:36:22.273762329 +0100
> +++ gcc/match.pd 2018-12-05 16:47:27.798596450 +0100
> @@ -312,17 +312,19 @@ (define_operator_list COND_TERNARY
> and floor_div is trickier and combining round_div even more so. */
> (for div (trunc_div exact_div)
> (simplify
> - (div (div @0 INTEGER_CST@1) INTEGER_CST@2)
> + (div (div@3 @0 INTEGER_CST@1) INTEGER_CST@2)
> (with {
> wi::overflow_type overflow;
> wide_int mul = wi::mul (wi::to_wide (@1), wi::to_wide (@2),
> TYPE_SIGN (type), &overflow);
> }
> - (if (!overflow)
> - (div @0 { wide_int_to_tree (type, mul); })
> - (if (TYPE_UNSIGNED (type)
> - || mul != wi::min_value (TYPE_PRECISION (type), SIGNED))
> - { build_zero_cst (type); })))))
> + (if (div == EXACT_DIV_EXPR
> + || optimize_successive_divisions_p (@2, @3))
> + (if (!overflow)
> + (div @0 { wide_int_to_tree (type, mul); })
> + (if (TYPE_UNSIGNED (type)
> + || mul != wi::min_value (TYPE_PRECISION (type), SIGNED))
> + { build_zero_cst (type); }))))))
>
> /* Combine successive multiplications. Similar to above, but handling
> overflow is different. */
> --- gcc/testsuite/gcc.dg/tree-ssa/pr85726-1.c.jj 2018-12-05
> 16:55:24.852680964 +0100
> +++ gcc/testsuite/gcc.dg/tree-ssa/pr85726-1.c 2018-12-05 16:50:14.489853926
> +0100
> @@ -0,0 +1,19 @@
> +/* PR tree-optimization/85726 */
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-tree-optimized" } */
> +/* { dg-final { scan-tree-dump " / 16;" "optimized" } } */
> +/* { dg-final { scan-tree-dump " / 3;" "optimized" } } */
> +/* { dg-final { scan-tree-dump " % 3;" "optimized" } } */
> +/* { dg-final { scan-tree-dump-not " / 48;" "optimized" } } */
> +
> +int ww, vv;
> +
> +int
> +foo (int y)
> +{
> + int z = y / 16;
> + int w = z / 3;
> + int v = z % 3;
> + ww = w;
> + return v;
> +}
> --- gcc/testsuite/gcc.dg/tree-ssa/pr85726-2.c.jj 2018-12-05
> 16:55:27.620634707 +0100
> +++ gcc/testsuite/gcc.dg/tree-ssa/pr85726-2.c 2018-12-05 16:51:25.636678886
> +0100
> @@ -0,0 +1,15 @@
> +/* PR tree-optimization/85726 */
> +/* { dg-do compile { target int32 } } */
> +/* { dg-options "-O2 -fdump-tree-optimized" } */
> +/* { dg-final { scan-tree-dump " / 3145728;" "optimized" } } */
> +/* { dg-final { scan-tree-dump "y = 0;" "optimized" } } */
> +
> +int x, y;
> +
> +void
> +foo (int n)
> +{
> + int c = 3 << 20;
> + x = n / c;
> + y = x / c;
> +}
> --- gcc/testsuite/gcc.dg/tree-ssa/pr85726-3.c.jj 2018-12-05
> 16:55:30.948579089 +0100
> +++ gcc/testsuite/gcc.dg/tree-ssa/pr85726-3.c 2018-12-05 16:52:57.350146115
> +0100
> @@ -0,0 +1,15 @@
> +/* PR tree-optimization/85726 */
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-tree-optimized" } */
> +/* { dg-final { scan-tree-dump-times " / 3;" 1 "optimized" } } */
> +/* { dg-final { scan-tree-dump-times " / 15;" 1 "optimized" } } */
> +
> +int x, y, z;
> +
> +void
> +foo (int n)
> +{
> + x = n / 3;
> + y = x / 5;
> + z = n / 15;
> +}
> --- gcc/testsuite/gcc.dg/tree-ssa/pr85726-4.c.jj 2018-12-05
> 16:55:34.588518255 +0100
> +++ gcc/testsuite/gcc.dg/tree-ssa/pr85726-4.c 2018-12-05 16:55:04.789016282
> +0100
> @@ -0,0 +1,15 @@
> +/* PR tree-optimization/85726 */
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-tree-optimized" } */
> +/* { dg-final { scan-tree-dump-times " / 4;" 1 "optimized" } } */
> +/* { dg-final { scan-tree-dump-times " / 16;" 1 "optimized" } } */
> +
> +int x, y, z;
> +
> +void
> +foo (int n)
> +{
> + x = n / 4;
> + y = x / 4;
> + z = y * 16 | 15;
> +}
>
> Jakub
>
>
--
Richard Biener <rguent...@suse.de>
SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB
21284 (AG Nuernberg)
