From: Kyrylo Tkachov <[email protected]>
A VECTOR_CST can encode a stepped series without storing every lane. The
fold-const negate_expr_p checks only the encoded elements. It can therefore
approve a signed vector whose implicit final lane is INT_MIN.
typedef int v4si __attribute__ ((vector_size (16)));
const v4si c = { 2147483645, 2147483646, 2147483647,
(-2147483647 - 1) };
v4si f (v4si x) { return (-x) - c; }
v4si g (v4si x) { return -(x + c); }
v4si h () { return -c; }
The old predicate lets f and g negate c. It represents -INT_MIN as INT_MIN,
which adds a false signed overflow for defined inputs. fold_negate_expr_1
can also negate the encoded elements of c directly. This removes the
required overflow diagnostic from h when overflow is instrumented.
aarch64 -O2 -fsanitize=signed-integer-overflow
-fsanitize-trap=signed-integer-overflow before:
h:
adrp x0, .LANCHOR0
ldr q0, [x0, #:lo12:.LANCHOR0]
ret
After:
h:
brk #1000
Reject a non-wrapping integral stepped vector in negate_expr_p. Also keep a
direct stepped integral negation when sanitizer instrumentation makes overflow
observable. Use vector-aware predicates directly. Keep the integral type
check before TYPE_OVERFLOW_WRAPS because fixed-point vectors can reach the
predicate, but TYPE_OVERFLOW_WRAPS does not accept them. The preceding patch
makes TYPE_OVERFLOW_SANITIZED accept integral vectors.
The two stepped checks have different conditions. negate_expr_p is a proof
for moving a negation. Moving an implicit INT_MIN negation can introduce
undefined overflow into f or g even when no overflow option is enabled, so
that predicate rejects every non-wrapping integral stepped constant.
fold_negate_expr_1 handles a direct source negation whose INT_MIN lane already
overflows. GCC normally folds that constant overflow, and -ftrapv does not
trap vector constant negation. Only sanitizer instrumentation makes the
missing operation observable, so the direct-fold check is conditional on
TYPE_OVERFLOW_SANITIZED.
The test checks that f and g do not report overflow for defined inputs. It
also checks that h reports its real INT_MIN negation.
Bootstrapped and tested on aarch64-none-linux-gnu and x86_64-pc-linux-gnu.
Ok for trunk?
Thanks,
Kyrill
gcc/ChangeLog:
* fold-const.cc (negate_expr_p): Reject non-wrapping stepped vector
constants.
(fold_negate_expr_1): Preserve sanitized stepped integral negations.
gcc/testsuite/ChangeLog:
* g++.dg/ubsan/fold-negate-vector-1.C: New test.
Signed-off-by: Kyrylo Tkachov <[email protected]>
---
gcc/fold-const.cc | 12 ++++-
.../g++.dg/ubsan/fold-negate-vector-1.C | 46 +++++++++++++++++++
2 files changed, 56 insertions(+), 2 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/ubsan/fold-negate-vector-1.C
diff --git a/gcc/fold-const.cc b/gcc/fold-const.cc
index 420e3185a2a..b2fc63ce5aa 100644
--- a/gcc/fold-const.cc
+++ b/gcc/fold-const.cc
@@ -406,10 +406,14 @@ negate_expr_p (tree t)
case VECTOR_CST:
{
- if (FLOAT_TYPE_P (TREE_TYPE (type)) || TYPE_OVERFLOW_WRAPS (type))
+ if (FLOAT_TYPE_P (type)
+ || (ANY_INTEGRAL_TYPE_P (type) && TYPE_OVERFLOW_WRAPS (type)))
return true;
- /* Steps don't prevent negation. */
+ /* An implicit element of a stepped vector can be the minimum
+ value. */
+ if (VECTOR_CST_STEPPED_P (t))
+ return false;
unsigned int count = vector_cst_encoded_nelts (t);
for (unsigned int i = 0; i < count; ++i)
if (!negate_expr_p (VECTOR_CST_ENCODED_ELT (t, i)))
@@ -566,6 +570,10 @@ fold_negate_expr_1 (location_t loc, tree t)
case VECTOR_CST:
{
+ if (VECTOR_CST_STEPPED_P (t)
+ && TYPE_OVERFLOW_SANITIZED (type))
+ return NULL_TREE;
+
tree_vector_builder elts;
elts.new_unary_operation (type, t, true);
unsigned int count = elts.encoded_nelts ();
diff --git a/gcc/testsuite/g++.dg/ubsan/fold-negate-vector-1.C
b/gcc/testsuite/g++.dg/ubsan/fold-negate-vector-1.C
new file mode 100644
index 00000000000..cda0fd9817f
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ubsan/fold-negate-vector-1.C
@@ -0,0 +1,46 @@
+// { dg-do run { target int32 } }
+// { dg-options "-O2 -Wno-psabi -fsanitize=signed-integer-overflow" }
+
+#define INT_MAX __INT_MAX__
+#define INT_MIN (-INT_MAX - 1)
+
+typedef int v4si __attribute__ ((vector_size (16)));
+
+const v4si c = { INT_MAX - 2, INT_MAX - 1, INT_MAX, INT_MIN };
+
+v4si __attribute__ ((noipa))
+f (v4si x)
+{
+ return (-x) - c;
+}
+
+v4si __attribute__ ((noipa))
+g (v4si x)
+{
+ return -(x + c);
+}
+
+v4si __attribute__ ((noipa))
+h ()
+{
+ return -c;
+}
+
+int
+main ()
+{
+ v4si x = { 0, 0, 0, 1 };
+ v4si y = f (x);
+ if (y[3] != INT_MAX)
+ __builtin_abort ();
+
+ y = g (x);
+ if (y[3] != INT_MAX)
+ __builtin_abort ();
+
+ volatile v4si z = h ();
+ if (z[3] != INT_MIN)
+ __builtin_abort ();
+}
+
+// { dg-output "negation of -2147483648 cannot be represented in type 'int';
cast to an unsigned type to negate this value to itself" }
--
2.50.1 (Apple Git-155)
