[PATCH 9/14] Enforce whole-vector-shifts to always be by a whole number of elements

[Alan Lawrence <alan dot lawrence at arm dot com>]

The VEC_RSHIFT_EXPR is only ever used by the vectorizer in tree-vect-loop.c 
(vect_create_epilog_for_reduction), to shift the vector by a whole number of 
elements. The tree code allows more general shifts but only for integral types. 
This only causes pain and difficulty for backends (particularly for backends 
with different endiannesses), and enforcing that restriction for integral types 
too does no harm.

bootstrapped on aarch64-none-linux-gnu and x86-64-none-linux-gnu
check-gcc on aarch64-none-elf and x86_64-none-linux-gnu

gcc/ChangeLog:

	* tree-cfg.c (verify_gimple_assign_binary): for VEC_RSHIFT_EXPR (and
	VEC_LSHIFT_EXPR), require shifts to be by a whole number of elements
	for all types, rather than only non-integral types.

	* tree.def (VEC_LSHIFT_EXPR, VEC_RSHIFT_EXPR): Update comment.

	* doc/md.texi (vec_shl_m, vec_shr_m): Update comment.

diff --git a/gcc/doc/md.texi b/gcc/doc/md.texi
index 3f5fd6f0e3ac3fcc30f6c961e3e2709a35f4d413..a78aea2f3f6e35b0d89719a42d734e62a2f5bd65 100644
--- a/gcc/doc/md.texi
+++ b/gcc/doc/md.texi
@@ -4888,7 +4888,8 @@ of a wider mode.)
 @item @samp{vec_shl_@var{m}}, @samp{vec_shr_@var{m}}
 Whole vector left/right shift in bits.
 Operand 1 is a vector to be shifted.
-Operand 2 is an integer shift amount in bits.
+Operand 2 is an integer shift amount in bits, which must be a multiple of the
+element size.
 Operand 0 is where the resulting shifted vector is stored.
 The output and input vectors should have the same modes.
 
diff --git a/gcc/tree-cfg.c b/gcc/tree-cfg.c
index 49986cc40758bb5998e395c727142e75f7d6e9f4..1ea2e256b09b25331810a57a9c35e5cc875d0404 100644
--- a/gcc/tree-cfg.c
+++ b/gcc/tree-cfg.c
@@ -3667,14 +3667,11 @@ verify_gimple_assign_binary (gimple stmt)
 	    debug_generic_expr (rhs2_type);
 	    return true;
 	  }
-	/* For shifting a vector of non-integral components we
-	   only allow shifting by a constant multiple of the element size.  */
-	if (!INTEGRAL_TYPE_P (TREE_TYPE (rhs1_type))
-	    && (TREE_CODE (rhs2) != INTEGER_CST
-		|| !div_if_zero_remainder (rhs2,
-					   TYPE_SIZE (TREE_TYPE (rhs1_type)))))
+	/* All shifts must be by a constant multiple of the element size.  */
+	if (TREE_CODE (rhs2) != INTEGER_CST
+	    || !div_if_zero_remainder (rhs2, TYPE_SIZE (TREE_TYPE (rhs1_type))))
 	  {
-	    error ("non-element sized vector shift of floating point vector");
+	    error ("non-element sized vector shift");
 	    return true;
 	  }
 
diff --git a/gcc/tree.def b/gcc/tree.def
index e9af52e554babb100d49ea14f47c805cd5024949..5406ffe67c53ff3f12920ca8c965cf0740a079c2 100644
--- a/gcc/tree.def
+++ b/gcc/tree.def
@@ -1240,7 +1240,8 @@ DEFTREECODE (FMA_EXPR, "fma_expr", tcc_expression, 3)
 
 /* Whole vector left/right shift in bits.
    Operand 0 is a vector to be shifted.
-   Operand 1 is an integer shift amount in bits.  */
+   Operand 1 is an integer shift amount in bits, which must be a multiple of the
+   element size.  */
 DEFTREECODE (VEC_LSHIFT_EXPR, "vec_lshift_expr", tcc_binary, 2)
 DEFTREECODE (VEC_RSHIFT_EXPR, "vec_rshift_expr", tcc_binary, 2)