From: Kyrylo Tkachov <[email protected]>
The PR71636 fold turns
x & ((1U << b) - 1)
into
x & ~(~0U << b)
but only when the mask type is unsigned. Signed source and vector forms keep
the longer expression.
int f (int x, int b)
{
return x & ((1 << b) - 1);
}
aarch64 -O2 before:
f:
mov w2, 1
lsl w2, w2, w1
sub w2, w2, #1
and w0, w2, w0
ret
aarch64 -O2 after:
f:
mov w2, -1
lsl w2, w2, w1
bic w0, w0, w2
ret
Build a signed mask in the corresponding unsigned type and convert it back.
This makes the all-ones shift defined and exposes the shorter form. Accept
both the canonical addition of minus one and a direct subtraction so the rule
also handles vector expressions.
The signed form is not valid when the source subtraction can trap or is
instrumented for overflow. It can also remove the signed shift-base check for
the top-bit count. Keep these cases. After GIMPLE lowering, an explicit
shift sanitizer check remains visible, so the fold is safe again.
Bootstrapped and tested on aarch64-none-linux-gnu.
Ok for trunk?
Thanks,
Kyrill
gcc/ChangeLog:
* match.pd (x & ((1 << b) - 1)): Handle signed scalar and vector
types.
gcc/testsuite/ChangeLog:
* gcc.dg/tree-ssa/pr71636-signed-1.c: New test.
* gcc.dg/tree-ssa/pr71636-signed-vector-1.c: Likewise.
* gcc.dg/tree-ssa/pr71636-signed-trap-1.c: Likewise.
* gcc.dg/tree-ssa/pr71636-signed-ubsan-1.c: Likewise.
* gcc.dg/tree-ssa/pr71636-signed-shift-ubsan-1.c: Likewise.
Signed-off-by: Kyrylo Tkachov <[email protected]>
---
gcc/match.pd | 23 ++++++++++++++----
.../gcc.dg/tree-ssa/pr71636-signed-1.c | 24 +++++++++++++++++++
.../tree-ssa/pr71636-signed-shift-ubsan-1.c | 11 +++++++++
.../gcc.dg/tree-ssa/pr71636-signed-trap-1.c | 10 ++++++++
.../gcc.dg/tree-ssa/pr71636-signed-ubsan-1.c | 10 ++++++++
.../gcc.dg/tree-ssa/pr71636-signed-vector-1.c | 24 +++++++++++++++++++
6 files changed, 97 insertions(+), 5 deletions(-)
create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr71636-signed-1.c
create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr71636-signed-shift-ubsan-1.c
create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr71636-signed-trap-1.c
create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr71636-signed-ubsan-1.c
create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr71636-signed-vector-1.c
diff --git a/gcc/match.pd b/gcc/match.pd
index 02684d8a302..4ead7bc316c 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -1558,11 +1558,24 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
(convert @0)
(convert @1)))))
-/* PR71636: Transform x & ((1U << b) - 1) -> x & ~(~0U << b); */
-(simplify
- (bit_and:c @0 (plus:s (lshift:s integer_onep @1) integer_minus_onep))
- (if (TYPE_UNSIGNED (type))
- (bit_and @0 (bit_not (lshift { build_all_ones_cst (type); } @1)))))
+/* PR71636: Transform x & ((1U << b) - 1) -> x & ~(~0U << b). For signed
+ types, build the mask in the corresponding unsigned type, where shifting
+ all ones left is defined. Preserve signed overflow and shift checks. */
+(for sub (plus minus)
+ (simplify
+ (bit_and:c @0
+ (sub:s (lshift:s integer_onep @1) uniform_integer_cst_p@2))
+ (with { tree cst = uniform_integer_cst_p (@2);
+ tree etype = VECTOR_TYPE_P (type) ? TREE_TYPE (type) : type; }
+ (if ((sub == PLUS_EXPR ? integer_minus_onep (cst) : integer_onep (cst))
+ && INTEGRAL_TYPE_P (etype)
+ && (TYPE_UNSIGNED (etype)
+ || (!TYPE_OVERFLOW_TRAPS (etype)
+ && !TYPE_OVERFLOW_SANITIZED (etype)
+ && (GIMPLE || !sanitize_flags_p (SANITIZE_SHIFT_BASE)))))
+ (with { tree utype = unsigned_type_for (type); }
+ (bit_and @0 (convert
+ (bit_not (lshift { build_all_ones_cst (utype); } @1)))))))))
(for bitop (bit_and bit_ior)
cmp (eq ne)
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr71636-signed-1.c b/gcc/testsuite/gcc.dg/tree-ssa/pr71636-signed-1.c
new file mode 100644
index 00000000000..9db533fdf64
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr71636-signed-1.c
@@ -0,0 +1,24 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+
+int
+f_signed (int x, int b)
+{
+ return x & ((1 << b) - 1);
+}
+
+unsigned int
+f_unsigned (unsigned int x, int b)
+{
+ return x & ((1U << b) - 1U);
+}
+
+long
+f_long (long x, int b)
+{
+ return x & ((1L << b) - 1L);
+}
+
+/* { dg-final { scan-tree-dump-not "1 <<" "optimized" } } */
+/* { dg-final { scan-tree-dump-not " \\+ -1;" "optimized" } } */
+/* { dg-final { scan-tree-dump-times "= ~" 3 "optimized" } } */
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr71636-signed-shift-ubsan-1.c b/gcc/testsuite/gcc.dg/tree-ssa/pr71636-signed-shift-ubsan-1.c
new file mode 100644
index 00000000000..3abee74264c
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr71636-signed-shift-ubsan-1.c
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fsanitize=shift-base -fdump-tree-optimized" } */
+
+int
+f (int x, int b)
+{
+ return x & ((1 << b) - 1);
+}
+
+/* { dg-final { scan-tree-dump-times "__builtin___ubsan_handle_shift_out_of_bounds" 1 "optimized" } } */
+/* { dg-final { scan-tree-dump-times "= ~" 1 "optimized" } } */
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr71636-signed-trap-1.c b/gcc/testsuite/gcc.dg/tree-ssa/pr71636-signed-trap-1.c
new file mode 100644
index 00000000000..13a1a5b4cf2
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr71636-signed-trap-1.c
@@ -0,0 +1,10 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -ftrapv -fdump-tree-optimized" } */
+
+int
+f (int x, int b)
+{
+ return x & ((1 << b) - 1);
+}
+
+/* { dg-final { scan-tree-dump-times " \\+ -1;" 1 "optimized" } } */
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr71636-signed-ubsan-1.c b/gcc/testsuite/gcc.dg/tree-ssa/pr71636-signed-ubsan-1.c
new file mode 100644
index 00000000000..68c1b92f18b
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr71636-signed-ubsan-1.c
@@ -0,0 +1,10 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fsanitize=signed-integer-overflow -fdump-tree-optimized" } */
+
+int
+f (int x, int b)
+{
+ return x & ((1 << b) - 1);
+}
+
+/* { dg-final { scan-tree-dump-times "\\.UBSAN_CHECK_SUB" 1 "optimized" } } */
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr71636-signed-vector-1.c b/gcc/testsuite/gcc.dg/tree-ssa/pr71636-signed-vector-1.c
new file mode 100644
index 00000000000..51ba0b35334
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr71636-signed-vector-1.c
@@ -0,0 +1,24 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+/* { dg-require-effective-target vect_int } */
+/* { dg-require-effective-target vect_var_shift } */
+
+typedef int v4si __attribute__ ((vector_size (16)));
+typedef unsigned int v4ui __attribute__ ((vector_size (16)));
+
+v4si
+f_signed (v4si x, v4si b)
+{
+ v4si one = { 1, 1, 1, 1 };
+ return x & ((one << b) - one);
+}
+
+v4ui
+f_unsigned (v4ui x, v4ui b)
+{
+ v4ui one = { 1, 1, 1, 1 };
+ return x & ((one << b) - one);
+}
+
+/* { dg-final { scan-tree-dump-not "\\{ 1, 1, 1, 1 \\} <<" "optimized" } } */
+/* { dg-final { scan-tree-dump-times "= ~" 2 "optimized" } } */
--
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