fold-const: Fix up fold_read_from_vector [PR100887]

The callers of fold_read_from_vector expect that the index they pass is
an index of an element in the vector and the function does that most of the
time.  But we allow CONSTRUCTORs with VECTOR_TYPE to have VECTOR_TYPE
elements and in that case every CONSTRUCTOR element represents not just one
index (with the exception of V1 vectors), but multiple.
So returning zero vector if i >= CONSTRUCTOR_NELTS or returning some
CONSTRUCTOR_ELT's value might not be what the callers expect.

Fixed by punting if the first element has vector type.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

In theory we could instead recurse (and assert that for CONSTRUCTORs of
vector elements we have always all elements specified like tree-cfg.c
verifies?) after adjusting the index appropriately.

2021-06-07  Jakub Jelinek  <jakub@redhat.com>

	PR target/100887
	* fold-const.c (fold_read_from_vector): Return NULL if trying to
	read from a CONSTRUCTOR with vector type elements.

	* gcc.dg/pr100887.c: New test.

diff --git a/gcc/fold-const.c b/gcc/fold-const.c
index 33d64bf..6e5835a 100644 (file)
--- a/gcc/fold-const.c
+++ b/gcc/fold-const.c
@@ -15471,6 +15471,9 @@ fold_read_from_vector (tree arg, poly_uint64 idx)
        return VECTOR_CST_ELT (arg, i);
       else if (TREE_CODE (arg) == CONSTRUCTOR)
        {
+         if (CONSTRUCTOR_NELTS (arg)
+             && VECTOR_TYPE_P (TREE_TYPE (CONSTRUCTOR_ELT (arg, 0)->value)))
+           return NULL_TREE;
          if (i >= CONSTRUCTOR_NELTS (arg))
            return build_zero_cst (TREE_TYPE (TREE_TYPE (arg)));
          return CONSTRUCTOR_ELT (arg, i)->value;

diff --git a/gcc/testsuite/gcc.dg/pr100887.c b/gcc/testsuite/gcc.dg/pr100887.c
new file mode 100644 (file)
index 0000000..de6b3ef
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr100887.c
@@ -0,0 +1,14 @@
+/* PR target/100887 */
+/* { dg-do compile } */
+/* { dg-options "" } */
+/* { dg-additional-options "-mavx512f" { target { i?86-*-* x86_64-*-* } } } */
+
+typedef unsigned long long __attribute__((__vector_size__ (2 * sizeof (long long)))) U;
+typedef unsigned long long __attribute__((__vector_size__ (4 * sizeof (long long)))) V;
+typedef unsigned long long __attribute__((__vector_size__ (8 * sizeof (long long)))) W;
+
+U
+foo (V v)
+{
+  return __builtin_shufflevector ((W){}, v, 0, 8);
+}