Our ifcombine pass combines 2 single-bit tests into a single test of
the form "(a & T) == T".
However, detection of the bit-tests does not work for sign-bits (of
any mode) as the RTL presented to the pass uses a cast to a
signed-type and an order-operator. E.g., the test for 'a & 0x80'
presents as:
_1 = *a_5(D);
_2 = (signed char) _1;
if (_2 < 0)
goto <bb 3>;
else
goto <bb 5>;
This adds detection logic to recognize_single_bit_test() for this case
and reports it as a single-bit test.
gcc/ChangeLog:
* tree-ssa-ifcombine.cc (recognize_single_bit_test): Add
detection for tests against the sign-bit of the relevant
type as a single-bit test.
gcc/testsuite/ChangeLog:
* gcc.dg/tree-ssa/ssa-ifcombine-14.c: New test.
Signed-off-by: Philipp Tomsich <[email protected]>
---
.../gcc.dg/tree-ssa/ssa-ifcombine-14.c | 14 +++++++++++++
gcc/tree-ssa-ifcombine.cc | 20 +++++++++++++++++++
2 files changed, 34 insertions(+)
create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/ssa-ifcombine-14.c
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-ifcombine-14.c
b/gcc/testsuite/gcc.dg/tree-ssa/ssa-ifcombine-14.c
new file mode 100644
index 00000000000..f9b1115a34a
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-ifcombine-14.c
@@ -0,0 +1,14 @@
+/* { dg-do compile } */
+/* { dg-options "-O -fdump-tree-ifcombine-details-blocks" } */
+
+void sink();
+
+void same(unsigned char *a)
+{
+ if (*a & 0x80)
+ if (*a & 0x40)
+ 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 80c41c45489..cd6331f84db 100644
--- a/gcc/tree-ssa-ifcombine.cc
+++ b/gcc/tree-ssa-ifcombine.cc
@@ -225,6 +225,26 @@ recognize_single_bit_test (gcond *cond, tree *name, tree
*bit, bool inv)
{
gimple *stmt;
+ /* Handle the test for a sign-bit:
+ unsigned charD.15 _1;
+ _2 = (signed char) _1;
+ if (_2 < 0) */
+ if (TREE_CODE (gimple_cond_lhs (cond)) == SSA_NAME
+ && !TYPE_UNSIGNED (TREE_TYPE (gimple_cond_lhs (cond)))
+ && gimple_cond_code (cond) == (inv ? GE_EXPR : LT_EXPR)
+ && integer_zerop (gimple_cond_rhs (cond)))
+ {
+ tree type = TREE_TYPE (gimple_cond_lhs (cond));
+
+ stmt = SSA_NAME_DEF_STMT (gimple_cond_lhs (cond));
+ if (!is_gimple_assign (stmt))
+ return false;
+ *name = gimple_assign_rhs1 (stmt);
+ *bit = build_int_cst (integer_type_node, TYPE_PRECISION (type) - 1);
+
+ return true;
+ }
+
/* Get at the definition of the result of the bit test. */
if (gimple_cond_code (cond) != (inv ? EQ_EXPR : NE_EXPR)
|| TREE_CODE (gimple_cond_lhs (cond)) != SSA_NAME
--
2.34.1
