* [PATCH] ifcombine: fold two bit tests with different polarity
@ 2022-11-09 23:08 Philipp Tomsich
2022-11-10 7:02 ` Richard Biener
0 siblings, 1 reply; 2+ messages in thread
From: Philipp Tomsich @ 2022-11-09 23:08 UTC (permalink / raw)
To: gcc-patches
Cc: Christoph Muellner, Tamar Christina, Jiang-Ning Liu,
Richard Biener, Jeff Law, Philipp Tomsich
Our ifcombine pass combines 2 single-bit tests into a single test of
the form "(a & T) == T", requiring the same polarity (i.e., tests for
bit set/cleared) for both bit-tests. However some applications test
against two bits expecting one set and the other cleared.
This adds support for the case "(a & T) == C" where T is a constant
with 2 bits set and C has only one of those bits set.
gcc/ChangeLog:
* tree-ssa-ifcombine.cc (ifcombine_ifandif): Add support for
combining two bit-tests that test for bits of different
polarity.
gcc/testsuite/ChangeLog:
* gcc.dg/tree-ssa/ssa-ifcombine-15.c: New test.
Signed-off-by: Philipp Tomsich <philipp.tomsich@vrull.eu>
---
.../gcc.dg/tree-ssa/ssa-ifcombine-15.c | 14 +++++
gcc/tree-ssa-ifcombine.cc | 56 +++++++++++++++++++
2 files changed, 70 insertions(+)
create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/ssa-ifcombine-15.c
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-ifcombine-15.c b/gcc/testsuite/gcc.dg/tree-ssa/ssa-ifcombine-15.c
new file mode 100644
index 00000000000..081faa39628
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-ifcombine-15.c
@@ -0,0 +1,14 @@
+/* { dg-do compile } */
+/* { dg-options "-O -fdump-tree-ifcombine-details-blocks" } */
+
+void sink();
+
+void reversed(unsigned char *a)
+{
+ if (*a & 0x60)
+ if (!(*a & 0x02))
+ g();
+}
+
+/* { dg-final { scan-tree-dump "optimizing double bit test" } } */
+
diff --git a/gcc/tree-ssa-ifcombine.cc b/gcc/tree-ssa-ifcombine.cc
index cd6331f84db..ea49cc2bff1 100644
--- a/gcc/tree-ssa-ifcombine.cc
+++ b/gcc/tree-ssa-ifcombine.cc
@@ -498,6 +498,62 @@ ifcombine_ifandif (basic_block inner_cond_bb, bool inner_inv,
return true;
}
+ /* See if we test polarity-reversed single bits of the same name in
+ both tests. In that case remove the outer test, merging both
+ else edges, and change the inner one to test for
+ name & (bit1 | bit2) == (bit2). */
+ else if ((recognize_single_bit_test (inner_cond, &name1, &bit1, !inner_inv)
+ && recognize_single_bit_test (outer_cond, &name2, &bit2, outer_inv)
+ && name1 == name2)
+ || (recognize_single_bit_test (inner_cond, &name2, &bit2, inner_inv)
+ && recognize_single_bit_test (outer_cond, &name1, &bit1, !outer_inv)
+ && name1 == name2))
+ {
+ tree t, t2, t3;
+
+ /* Do it. */
+ gsi = gsi_for_stmt (inner_cond);
+ t = fold_build2 (LSHIFT_EXPR, TREE_TYPE (name1),
+ build_int_cst (TREE_TYPE (name1), 1), bit1);
+ t2 = fold_build2 (LSHIFT_EXPR, TREE_TYPE (name1),
+ build_int_cst (TREE_TYPE (name1), 1), bit2);
+ t = fold_build2 (BIT_IOR_EXPR, TREE_TYPE (name1), t, t2);
+ t = force_gimple_operand_gsi (&gsi, t, true, NULL_TREE,
+ true, GSI_SAME_STMT);
+ t3 = fold_build2 (BIT_AND_EXPR, TREE_TYPE (name1), name1, t);
+ t3 = force_gimple_operand_gsi (&gsi, t3, true, NULL_TREE,
+ true, GSI_SAME_STMT);
+ t = fold_build2 (result_inv ? NE_EXPR : EQ_EXPR,
+ boolean_type_node, t2, t3);
+ t = canonicalize_cond_expr_cond (t);
+ if (!t)
+ return false;
+ gimple_cond_set_condition_from_tree (inner_cond, t);
+ update_stmt (inner_cond);
+
+ /* Leave CFG optimization to cfg_cleanup. */
+ gimple_cond_set_condition_from_tree (outer_cond,
+ outer_inv ? boolean_false_node : boolean_true_node);
+ update_stmt (outer_cond);
+
+ update_profile_after_ifcombine (inner_cond_bb, outer_cond_bb);
+
+ if (dump_file)
+ {
+ fprintf (dump_file, "optimizing double bit test to ");
+ print_generic_expr (dump_file, name1);
+ fprintf (dump_file, " & T == C\nwith temporary T = (1 << ");
+ print_generic_expr (dump_file, bit1);
+ fprintf (dump_file, ") | (1 << ");
+ print_generic_expr (dump_file, bit2);
+ fprintf (dump_file, ")\nand temporary C = (1 << ");
+ print_generic_expr (dump_file, bit2);
+ fprintf (dump_file, ")\n");
+ }
+
+ return true;
+ }
+
/* See if we have two bit tests of the same name in both tests.
In that case remove the outer test and change the inner one to
test for name & (bits1 | bits2) != 0. */
--
2.34.1
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [PATCH] ifcombine: fold two bit tests with different polarity
2022-11-09 23:08 [PATCH] ifcombine: fold two bit tests with different polarity Philipp Tomsich
@ 2022-11-10 7:02 ` Richard Biener
0 siblings, 0 replies; 2+ messages in thread
From: Richard Biener @ 2022-11-10 7:02 UTC (permalink / raw)
To: Philipp Tomsich
Cc: gcc-patches, Christoph Muellner, Tamar Christina, Jiang-Ning Liu,
Jeff Law
On Thu, 10 Nov 2022, Philipp Tomsich wrote:
> Our ifcombine pass combines 2 single-bit tests into a single test of
> the form "(a & T) == T", requiring the same polarity (i.e., tests for
> bit set/cleared) for both bit-tests. However some applications test
> against two bits expecting one set and the other cleared.
>
> This adds support for the case "(a & T) == C" where T is a constant
> with 2 bits set and C has only one of those bits set.
>
> gcc/ChangeLog:
>
> * tree-ssa-ifcombine.cc (ifcombine_ifandif): Add support for
> combining two bit-tests that test for bits of different
> polarity.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.dg/tree-ssa/ssa-ifcombine-15.c: New test.
>
> Signed-off-by: Philipp Tomsich <philipp.tomsich@vrull.eu>
> ---
>
> .../gcc.dg/tree-ssa/ssa-ifcombine-15.c | 14 +++++
> gcc/tree-ssa-ifcombine.cc | 56 +++++++++++++++++++
> 2 files changed, 70 insertions(+)
> create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/ssa-ifcombine-15.c
>
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-ifcombine-15.c b/gcc/testsuite/gcc.dg/tree-ssa/ssa-ifcombine-15.c
> new file mode 100644
> index 00000000000..081faa39628
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-ifcombine-15.c
> @@ -0,0 +1,14 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O -fdump-tree-ifcombine-details-blocks" } */
> +
> +void sink();
> +
> +void reversed(unsigned char *a)
> +{
> + if (*a & 0x60)
> + if (!(*a & 0x02))
> + g();
> +}
> +
> +/* { dg-final { scan-tree-dump "optimizing double bit test" } } */
> +
> diff --git a/gcc/tree-ssa-ifcombine.cc b/gcc/tree-ssa-ifcombine.cc
> index cd6331f84db..ea49cc2bff1 100644
> --- a/gcc/tree-ssa-ifcombine.cc
> +++ b/gcc/tree-ssa-ifcombine.cc
> @@ -498,6 +498,62 @@ ifcombine_ifandif (basic_block inner_cond_bb, bool inner_inv,
> return true;
> }
>
> + /* See if we test polarity-reversed single bits of the same name in
> + both tests. In that case remove the outer test, merging both
> + else edges, and change the inner one to test for
> + name & (bit1 | bit2) == (bit2). */
> + else if ((recognize_single_bit_test (inner_cond, &name1, &bit1, !inner_inv)
> + && recognize_single_bit_test (outer_cond, &name2, &bit2, outer_inv)
> + && name1 == name2)
> + || (recognize_single_bit_test (inner_cond, &name2, &bit2, inner_inv)
> + && recognize_single_bit_test (outer_cond, &name1, &bit1, !outer_inv)
> + && name1 == name2))
Instead of explicitely testing for the combinations of !inv and inv can
you make recognize_single_bit_test output whether it recognizes a bit
set or bit clear pattern and then appropriately combine that with
inner_inv/outer_inv to the correct test? It seems we can handle all cases
just fine?
Thanks,
Richard.
> + {
> + tree t, t2, t3;
> +
> + /* Do it. */
> + gsi = gsi_for_stmt (inner_cond);
> + t = fold_build2 (LSHIFT_EXPR, TREE_TYPE (name1),
> + build_int_cst (TREE_TYPE (name1), 1), bit1);
> + t2 = fold_build2 (LSHIFT_EXPR, TREE_TYPE (name1),
> + build_int_cst (TREE_TYPE (name1), 1), bit2);
> + t = fold_build2 (BIT_IOR_EXPR, TREE_TYPE (name1), t, t2);
> + t = force_gimple_operand_gsi (&gsi, t, true, NULL_TREE,
> + true, GSI_SAME_STMT);
> + t3 = fold_build2 (BIT_AND_EXPR, TREE_TYPE (name1), name1, t);
> + t3 = force_gimple_operand_gsi (&gsi, t3, true, NULL_TREE,
> + true, GSI_SAME_STMT);
> + t = fold_build2 (result_inv ? NE_EXPR : EQ_EXPR,
> + boolean_type_node, t2, t3);
> + t = canonicalize_cond_expr_cond (t);
> + if (!t)
> + return false;
> + gimple_cond_set_condition_from_tree (inner_cond, t);
> + update_stmt (inner_cond);
> +
> + /* Leave CFG optimization to cfg_cleanup. */
> + gimple_cond_set_condition_from_tree (outer_cond,
> + outer_inv ? boolean_false_node : boolean_true_node);
> + update_stmt (outer_cond);
> +
> + update_profile_after_ifcombine (inner_cond_bb, outer_cond_bb);
> +
> + if (dump_file)
> + {
> + fprintf (dump_file, "optimizing double bit test to ");
> + print_generic_expr (dump_file, name1);
> + fprintf (dump_file, " & T == C\nwith temporary T = (1 << ");
> + print_generic_expr (dump_file, bit1);
> + fprintf (dump_file, ") | (1 << ");
> + print_generic_expr (dump_file, bit2);
> + fprintf (dump_file, ")\nand temporary C = (1 << ");
> + print_generic_expr (dump_file, bit2);
> + fprintf (dump_file, ")\n");
> + }
> +
> + return true;
> + }
> +
> /* See if we have two bit tests of the same name in both tests.
> In that case remove the outer test and change the inner one to
> test for name & (bits1 | bits2) != 0. */
>
--
Richard Biener <rguenther@suse.de>
SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg,
Germany; GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman;
HRB 36809 (AG Nuernberg)
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