testsuite: Add a test case for negating FP vectors containing zeros

Recently I've fixed two wrong FP vector negate implementation which
caused wrong sign bits in zeros in targets (r14-8786 and r14-8801).  To
prevent a similar issue from happening again, add a test case.

Tested on x86_64 (with SSE2, AVX, AVX2, and AVX512F), AArch64, MIPS
(with MSA), LoongArch (with LSX and LASX).

gcc/testsuite:

	* gcc.dg/vect/vect-neg-zero.c: New test.

1 files changed, 38 insertions, 0 deletions

diff --git a/gcc/testsuite/gcc.dg/vect/vect-neg-zero.c b/gcc/testsuite/gcc.dg/vect/vect-neg-zero.c
new file mode 100644
index 0000000..21fa00c
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-neg-zero.c
@@ -0,0 +1,38 @@
+/* { dg-add-options ieee } */
+/* { dg-additional-options "-fno-associative-math -fsigned-zeros" } */
+
+double x[4] = {-0.0, 0.0, -0.0, 0.0};
+float y[8] = {-0.0, 0.0, -0.0, 0.0, -0.0, -0.0, 0.0, 0.0};
+
+static __attribute__ ((always_inline)) inline void
+test (int factor)
+{
+  double a[4];
+  float b[8];
+
+  asm ("" ::: "memory");
+
+  for (int i = 0; i < 2 * factor; i++)
+    a[i] = -x[i];
+
+  for (int i = 0; i < 4 * factor; i++)
+    b[i] = -y[i];
+
+#pragma GCC novector
+  for (int i = 0; i < 2 * factor; i++)
+    if (__builtin_signbit (a[i]) == __builtin_signbit (x[i]))
+      __builtin_abort ();
+
+#pragma GCC novector
+  for (int i = 0; i < 4 * factor; i++)
+    if (__builtin_signbit (b[i]) == __builtin_signbit (y[i]))
+      __builtin_abort ();
+}
+
+int
+main (void)
+{
+  test (1);
+  test (2);
+  return 0;
+}