These 2 routines were adding and subtracting 1 to a range bound, and
checking for overflow.
Signed 1 bit values have a range of [-1, 0]. Adding or subtracting 1
cannot be properly represented resulting in the overflow being set.
This caused us to set UNDEFINED when we shouldn't.
This patch changes it such that signed values always have -1 added or
subtracted as appropriate, allowing for proper representation and
overflow setting.
Bootstrapped on x86_64-pc-linux-gnu with no regressions. Pushed.
Andrew
commit 84f7bab89279ca1234fef88929c74caeda8cb55e
Author: Andrew MacLeod <amacl...@redhat.com>
Date: Wed Jun 30 14:15:53 2021 -0400
Fix build_gt and build_lt for signed 1 bit values.
Signed 1 bit values have a range of [-1, 0] but neither (0 - 1) nor (-1 + 1)
can be represented. For signed values, add or subtract -1 as appropriate.
PR tree-optimization/101223
gcc/
* range-op.cc (build_lt): Add -1 for signed values.
(built_gt): Subtract -1 for signed values.
gcc/testsuite/
* gcc.dg/pr101223.c: New.
diff --git a/gcc/range-op.cc b/gcc/range-op.cc
index 97b9843e095..f8e4c6d4e49 100644
--- a/gcc/range-op.cc
+++ b/gcc/range-op.cc
@@ -687,7 +687,14 @@ static void
build_lt (irange &r, tree type, const wide_int &val)
{
wi::overflow_type ov;
- wide_int lim = wi::sub (val, 1, TYPE_SIGN (type), &ov);
+ wide_int lim;
+ signop sgn = TYPE_SIGN (type);
+
+ // Signed 1 bit cannot represent 1 for subtraction.
+ if (sgn == SIGNED)
+ lim = wi::add (val, -1, sgn, &ov);
+ else
+ lim = wi::sub (val, 1, sgn, &ov);
// If val - 1 underflows, check if X < MIN, which is an empty range.
if (ov)
@@ -710,7 +717,14 @@ static void
build_gt (irange &r, tree type, const wide_int &val)
{
wi::overflow_type ov;
- wide_int lim = wi::add (val, 1, TYPE_SIGN (type), &ov);
+ wide_int lim;
+ signop sgn = TYPE_SIGN (type);
+
+ // Signed 1 bit cannot represent 1 for addition.
+ if (sgn == SIGNED)
+ lim = wi::sub (val, -1, sgn, &ov);
+ else
+ lim = wi::add (val, 1, sgn, &ov);
// If val + 1 overflows, check is for X > MAX, which is an empty range.
if (ov)
r.set_undefined ();
diff --git a/gcc/testsuite/gcc.dg/pr101223.c b/gcc/testsuite/gcc.dg/pr101223.c
new file mode 100644
index 00000000000..6d5a247fa6c
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr101223.c
@@ -0,0 +1,44 @@
+/* PR tree-optimization/101223 */
+/* { dg-do run } */
+/* { dg-options "-O2 " } */
+
+struct {
+ int a : 1;
+} b;
+int c = 1, d;
+int foo1() {
+ for (; d < 2; d++) {
+ int e = ~c, f = 0, g;
+ if (e) {
+ f = c;
+ g = b.a;
+ b.a = f;
+ if (b.a >= g)
+ __builtin_abort();
+ }
+ c = f;
+ b.a = g;
+ }
+ return 0;
+}
+
+int foo2() {
+ for (; d < 2; d++) {
+ int e = ~c, f = 0, g;
+ if (e) {
+ f = c;
+ g = b.a;
+ b.a = f;
+ if (g <= b.a)
+ __builtin_abort();
+ }
+ c = f;
+ b.a = g;
+ }
+ return 0;
+}
+int main ()
+{
+ return foo1() + foo2();
+}
+
