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* [PATCH] tree-optimization: [PR102622]: wrong code due to signed one bit integer and "a?-1:0"
@ 2021-10-10  5:42 apinski
  2021-10-10  8:03 ` Richard Biener
  2021-10-11 13:07 ` Michael Matz
  0 siblings, 2 replies; 3+ messages in thread
From: apinski @ 2021-10-10  5:42 UTC (permalink / raw)
  To: gcc-patches; +Cc: Andrew Pinski

From: Andrew Pinski <apinski@marvell.com>

So it turns out this is kinda of a latent bug but not really latent.
In GCC 9 and 10, phi-opt would transform a?-1:0 (even for signed 1-bit integer)
to -(type)a but the type is an one bit integer which means the negation is
undefined. GCC 11 fixed the problem by checking for a?pow2cst:0 transformation
before a?-1:0 transformation.

When I added the transformations to match.pd, I had swapped the order not paying
attention and I didn't expect anything of it. Because there was no testcase failing
due to this.
Anyways this fixes the problem on the trunk by swapping the order in match.pd and
adding a comment of why the order is this way.

I will try to come up with a patch for GCC 9 and 10 series later on which fixes
the problem there too.

Note I didn't include the original testcase which requires the vectorizer and AVX-512f
as I can't figure out the right dg options to restrict it to avx-512f but I did come up
with a testcase which shows the problem and even more shows the problem with the 9/10
series as mentioned.

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

	PR tree-optimization/102622

gcc/ChangeLog:

	* match.pd: Swap the order of a?pow2cst:0 and a?-1:0 transformations.
	Swap the order of a?0:pow2cst and a?0:-1 transformations.

gcc/testsuite/ChangeLog:

	* gcc.c-torture/execute/bitfld-10.c: New test.
---
 gcc/match.pd                                  | 26 ++++++++++++-------
 .../gcc.c-torture/execute/bitfld-10.c         | 24 +++++++++++++++++
 2 files changed, 41 insertions(+), 9 deletions(-)
 create mode 100644 gcc/testsuite/gcc.c-torture/execute/bitfld-10.c

diff --git a/gcc/match.pd b/gcc/match.pd
index 9d7c1ac637f..c153e9a6e98 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -3949,15 +3949,16 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
     /* a ? 1 : 0 -> a if 0 and 1 are integral types. */
     (if (integer_onep (@1))
      (convert (convert:boolean_type_node @0)))
-    /* a ? -1 : 0 -> -a. */
-    (if (INTEGRAL_TYPE_P (type) && integer_all_onesp (@1))
-     (negate (convert (convert:boolean_type_node @0))))
     /* a ? powerof2cst : 0 -> a << (log2(powerof2cst)) */
     (if (INTEGRAL_TYPE_P (type) && integer_pow2p (@1))
      (with {
        tree shift = build_int_cst (integer_type_node, tree_log2 (@1));
       }
-      (lshift (convert (convert:boolean_type_node @0)) { shift; })))))
+      (lshift (convert (convert:boolean_type_node @0)) { shift; })))
+    /* a ? -1 : 0 -> -a.  No need to check the TYPE_PRECISION not being 1
+       here as the powerof2cst case above will handle that case correctly.  */
+    (if (INTEGRAL_TYPE_P (type) && integer_all_onesp (@1))
+     (negate (convert (convert:boolean_type_node @0))))))
   (if (integer_zerop (@1))
    (with {
       tree booltrue = constant_boolean_node (true, boolean_type_node);
@@ -3966,16 +3967,23 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
      /* a ? 0 : 1 -> !a. */
      (if (integer_onep (@2))
       (convert (bit_xor (convert:boolean_type_node @0) { booltrue; } )))
-     /* a ? -1 : 0 -> -(!a). */
-     (if (INTEGRAL_TYPE_P (type) && integer_all_onesp (@2))
-      (negate (convert (bit_xor (convert:boolean_type_node @0) { booltrue; } ))))
      /* a ? powerof2cst : 0 -> (!a) << (log2(powerof2cst)) */
-     (if (INTEGRAL_TYPE_P (type) &&  integer_pow2p (@2))
+     (if (INTEGRAL_TYPE_P (type) &&  integer_pow2p (@2)
+         && TYPE_PRECISION (type) != 1)
       (with {
 	tree shift = build_int_cst (integer_type_node, tree_log2 (@2));
        }
        (lshift (convert (bit_xor (convert:boolean_type_node @0) { booltrue; } ))
-        { shift; }))))))))
+        { shift; })))
+     /* a ? -1 : 0 -> -(!a).  No need to check the TYPE_PRECISION not being 1
+       here as the powerof2cst case above will handle that case correctly.  */
+     (if (INTEGRAL_TYPE_P (type) && integer_all_onesp (@2))
+      (negate (convert (bit_xor (convert:boolean_type_node @0) { booltrue; } ))))
+    )
+   )
+  )
+ )
+)
 #endif
 
 /* Simplification moved from fold_cond_expr_with_comparison.  It may also
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 00000000000..bdbf5733ce7
--- /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;
+}
-- 
2.17.1


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2021-10-10  5:42 [PATCH] tree-optimization: [PR102622]: wrong code due to signed one bit integer and "a?-1:0" apinski
2021-10-10  8:03 ` Richard Biener
2021-10-11 13:07 ` Michael Matz

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