From: Kyrylo Tkachov <[email protected]>
The conditional-compare expander accepts a plain boolean as a comparison
against zero. This is useful when a chain also contains an explicit
comparison. It is harmful when every leaf is a boolean. For example:
_Bool
f (_Bool x, _Bool y)
{
return x || y;
}
AArch64 emitted:
and w1, w1, 255
tst w0, 255
ccmp w1, 0, 0, eq
cset w0, ne
After this patch it emits one bitwise operation:
orr w0, w0, w1
Require at least one explicit comparison in a conditional-compare tree.
Mixed boolean and comparison chains remain accepted.
Bootstrapped and tested on aarch64-none-linux-gnu.
Ok for trunk?
Thanks,
Kyrill
gcc/
PR middle-end/109832
* ccmp.cc (ccmp_tree_has_comparison_p): New function.
(expand_ccmp_expr): Reject an all-boolean tree.
gcc/testsuite/
PR middle-end/109832
* gcc.target/aarch64/ccmp_7.c: New test.
Signed-off-by: Kyrylo Tkachov <[email protected]>
---
gcc/ccmp.cc | 24 ++++++++++++
gcc/testsuite/gcc.target/aarch64/ccmp_7.c | 46 +++++++++++++++++++++++
2 files changed, 70 insertions(+)
create mode 100644 gcc/testsuite/gcc.target/aarch64/ccmp_7.c
diff --git a/gcc/ccmp.cc b/gcc/ccmp.cc
index 1c540f641b2..9f7670bf58e 100644
--- a/gcc/ccmp.cc
+++ b/gcc/ccmp.cc
@@ -93,6 +93,25 @@ ccmp_tree_comparison_p (tree t, basic_block bb)
typedef hash_map<tree, bool> ccmp_uniform_cache;
+/* Return true if AND/IOR tree T contains a comparison in BB. */
+
+static bool
+ccmp_tree_has_comparison_p (tree t, basic_block bb)
+{
+ gimple *g = get_gimple_for_ssa_name (t);
+ if (!g || !is_gimple_assign (g))
+ return false;
+
+ tree_code code = gimple_assign_rhs_code (g);
+ if (TREE_CODE_CLASS (code) == tcc_comparison)
+ return gimple_bb (g) == bb;
+ if (code != BIT_AND_EXPR && code != BIT_IOR_EXPR)
+ return false;
+
+ return (ccmp_tree_has_comparison_p (gimple_assign_rhs1 (g), bb)
+ || ccmp_tree_has_comparison_p (gimple_assign_rhs2 (g), bb));
+}
+
/* Return true if T is a CODE tree in BB whose leaves are comparisons.
CACHE records results for logical SSA definitions. */
@@ -368,6 +387,11 @@ expand_ccmp_expr (gimple *g, machine_mode mode)
if (!ccmp_candidate_p (g, cache, true))
return NULL_RTX;
+ basic_block bb = gimple_bb (g);
+ if (!ccmp_tree_has_comparison_p (gimple_assign_rhs1 (g), bb)
+ && !ccmp_tree_has_comparison_p (gimple_assign_rhs2 (g), bb))
+ return NULL_RTX;
+
last = get_last_insn ();
rtx_insn *prep_seq = NULL, *gen_seq = NULL;
diff --git a/gcc/testsuite/gcc.target/aarch64/ccmp_7.c
b/gcc/testsuite/gcc.target/aarch64/ccmp_7.c
new file mode 100644
index 00000000000..29e269b854e
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/ccmp_7.c
@@ -0,0 +1,46 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+/* PR middle-end/109832 */
+
+/* A conditional compare folds a comparison into the flags. When the operands
+ are plain booleans there is no comparison to fold and the bitwise operation
+ is cheaper, so no conditional compare should be formed. */
+
+_Bool
+bool_ior (_Bool x, _Bool y)
+{
+ return x || y;
+}
+
+_Bool
+bool_and (_Bool x, _Bool y)
+{
+ return x && y;
+}
+
+extern _Bool t (void);
+
+_Bool
+bool_call_ior (void)
+{
+ _Bool x = t ();
+ _Bool y = t ();
+ return x | y;
+}
+
+_Bool
+bool_ior_tree (_Bool a, _Bool b, _Bool c, _Bool d)
+{
+ return (a | b) | (c | d);
+}
+
+/* One explicit comparison is enough to keep each chain profitable. */
+
+int
+bool_and_cmp_tree (_Bool a, _Bool b, _Bool c, int x, int y)
+{
+ return ((a & b) & c) & (x < y);
+}
+
+/* { dg-final { scan-assembler-times {\tccmp\t} 3 } } */
+/* { dg-final { scan-assembler-times {\torr\t} 5 } } */
--
2.50.1 (Apple Git-155)
