[gcc r10-10261] middle-end/100672 - fix bogus right shift folding

[gcc r10-10261] middle-end/100672 - fix bogus right shift folding

[Richard Biener]

https://gcc.gnu.org/g:e8311f59c6e2fa1f5aacc3da5e95739886ebdee7

commit r10-10261-ge8311f59c6e2fa1f5aacc3da5e95739886ebdee7
Author: Richard Biener <rguenther@suse.de>
Date:   Wed May 19 13:35:07 2021 +0200

    middle-end/100672 - fix bogus right shift folding
    
    This fixes the bogus use of TYPE_PRECISION on vector types
    from optimizing -((int)x >> 31) into (unsigned)x >> 31.
    
    2021-05-19  Richard Biener  <rguenther@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.
    
    (cherry picked from commit 8d51039cb7c807ed84ff7df5416a1e3ba07a5e63)

Diff:
---
 gcc/fold-const.c                        |  4 ++--
 gcc/testsuite/gcc.dg/torture/pr100672.c | 19 +++++++++++++++++++
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/gcc/fold-const.c b/gcc/fold-const.c
index 6e635382fb4..7b4c9c0eb7f 100644
--- a/gcc/fold-const.c
+++ b/gcc/fold-const.c
@@ -511,7 +511,7 @@ 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;
@@ -704,7 +704,7 @@ 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;
+}