[PATCH] middle-end/100672 - fix bogus right shift folding

[Richard Biener]

This fixes the bogus use of TYPE_PRECISION on vector types
from optimizing -((int)x >> 31) into (unsigned)x >> 31.

Bootstrapped on x86_64-unknown-linux-gnu, testing in progress.

Richard.

2021-05-19  Richard Biener  <rguent...@suse.de>

        PR middle-end/100672
        * fold-const.c (fold_negate_expr_1): Use element_precision.
        (negate_expr_p): Likewise.

        * gcc.dg/torture/pr100672.c: New testcase.
---
 gcc/fold-const.c                        |  4 ++--
 gcc/testsuite/gcc.dg/torture/pr100672.c | 19 +++++++++++++++++++
 2 files changed, 21 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/torture/pr100672.c

diff --git a/gcc/fold-const.c b/gcc/fold-const.c
index 5a41524702b..3be9c15e6b2 100644
--- a/gcc/fold-const.c
+++ b/gcc/fold-const.c
@@ -512,7 +512,7 @@ negate_expr_p (tree t)
       if (TREE_CODE (TREE_OPERAND (t, 1)) == INTEGER_CST)
        {
          tree op1 = TREE_OPERAND (t, 1);
-         if (wi::to_wide (op1) == TYPE_PRECISION (type) - 1)
+         if (wi::to_wide (op1) == element_precision (type) - 1)
            return true;
        }
       break;
@@ -705,7 +705,7 @@ fold_negate_expr_1 (location_t loc, tree t)
       if (TREE_CODE (TREE_OPERAND (t, 1)) == INTEGER_CST)
        {
          tree op1 = TREE_OPERAND (t, 1);
-         if (wi::to_wide (op1) == TYPE_PRECISION (type) - 1)
+         if (wi::to_wide (op1) == element_precision (type) - 1)
            {
              tree ntype = TYPE_UNSIGNED (type)
                           ? signed_type_for (type)
diff --git a/gcc/testsuite/gcc.dg/torture/pr100672.c 
b/gcc/testsuite/gcc.dg/torture/pr100672.c
new file mode 100644
index 00000000000..cc62e71f9a3
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr100672.c
@@ -0,0 +1,19 @@
+/* { dg-do run } */
+/* { dg-additional-options "-w -Wno-psabi" } */
+
+typedef long long __attribute__((__vector_size__ (4 * sizeof (long long)))) V;
+
+V
+foo (V v)
+{
+  return -(v >> 1);
+}
+
+int
+main (void)
+{
+  V v = foo ((V) { -2, -4, -6, -8 });
+  if (v[0] != 1 || v[1] != 2 || v[2] != 3 || v[3] != 4)
+    __builtin_abort ();
+  return 0;
+}
-- 
2.26.2