[PATCH] [GCC 10 branch] tree-optimization: [PR102622]: wrong code due to signed one bit integer and "a?-1:0"

[apinski--- via Gcc-patches]

From: Andrew Pinski <apin...@marvell.com>

So here is the GCC 10 branch version which fixes the wrong code.
The problem is we create a negation of an one bit signed integer type
which is undefined if the value was -1.
This is not needed for GCC 11 branch since the case is handled differently
there and has been fixed there (and the trunk has now been fixed too).
So for one bit types, there is no reason to create the negation so just
setting neg to false for them, just works.

OK? Bootstrapped and tested on x86_64-linux-gnu.

        PR tree-optimization/102622

gcc/ChangeLog:

        * tree-ssa-phiopt.c (conditional_replacement): Set neg
        to false for one bit signed types.

gcc/testsuite/ChangeLog:

        * gcc.c-torture/execute/bitfld-10.c: New test.
---
 gcc/testsuite/gcc.c-torture/execute/bitfld-10.c | 24 ++++++++++++++++++++++++
 gcc/tree-ssa-phiopt.c                           |  5 ++++-
 2 files changed, 28 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/gcc.c-torture/execute/bitfld-10.c

diff --git a/gcc/testsuite/gcc.c-torture/execute/bitfld-10.c 
b/gcc/testsuite/gcc.c-torture/execute/bitfld-10.c
new file mode 100644
index 0000000..bdbf573
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/execute/bitfld-10.c
@@ -0,0 +1,24 @@
+/* PR tree-optimization/102622 */
+/* Wrong code introduced due to phi-opt
+   introducing undefined signed interger overflow
+   with one bit signed integer negation. */
+
+struct f{signed t:1;};
+int g(struct f *a, int t) __attribute__((noipa));
+int g(struct f *a, int t)
+{
+    if (t)
+      a->t = -1;
+    else
+      a->t = 0;
+    int t1 = a->t;
+    if (t1) return 1;
+    return t1;
+}
+
+int main(void)
+{
+    struct f a;
+    if (!g(&a, 1))  __builtin_abort();
+    return 0;
+}
diff --git a/gcc/tree-ssa-phiopt.c b/gcc/tree-ssa-phiopt.c
index 9ed26a3..a6c197d 100644
--- a/gcc/tree-ssa-phiopt.c
+++ b/gcc/tree-ssa-phiopt.c
@@ -770,9 +770,12 @@ conditional_replacement (basic_block cond_bb, basic_block 
middle_bb,
   if ((integer_zerop (arg0) && integer_onep (arg1))
       || (integer_zerop (arg1) && integer_onep (arg0)))
     neg = false;
+  /* For signed one bit types, the negation is not needed and
+     should be avoided and is the same as 1 case for non-signed
+     one bit types.  */
   else if ((integer_zerop (arg0) && integer_all_onesp (arg1))
           || (integer_zerop (arg1) && integer_all_onesp (arg0)))
-    neg = true;
+    neg = TYPE_PRECISION (TREE_TYPE (arg0)) != 1;
   else
     return false;
 
-- 
1.8.3.1