diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 95e24a3c47d42c448a337a29e119b213fc6ef6f5..bc704067bf063cf04f9c426dd04cda86a3293cf1 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,13 @@
+2017-08-30  Richard Sandiford  <richard.sandiford@linaro.org>
+	    Alan Hayward  <alan.hayward@arm.com>
+	    David Sherwood  <david.sherwood@arm.com>
+
+	* machmode.h (mode_for_vector): Take a scalar_mode instead
+	of a machine_mode.
+	* stor-layout.c (mode_for_vector): Likewise.
+	* explow.c (promote_mode): Use as_a <scalar_mode>.
+	* sdbout.c (sdbout_parms): Use is_a <scalar_mode>.
+
 2017-08-30  Richard Sandiford  <richard.sandiford@linaro.org>
 	    Alan Hayward  <alan.hayward@arm.com>
 	    David Sherwood  <david.sherwood@arm.com>
diff --git a/gcc/explow.c b/gcc/explow.c
index ee20969d23a52e642b39d188d380e2388635a76c..82380f31093c629e6d676b81521e56cb61d10ad3 100644
--- a/gcc/explow.c
+++ b/gcc/explow.c
@@ -787,6 +787,7 @@ promote_mode (const_tree type ATTRIBUTE_UNUSED, machine_mode mode,
 #ifdef PROMOTE_MODE
   enum tree_code code;
   int unsignedp;
+  scalar_mode smode;
 #endif
 
   /* For libcalls this is invoked without TYPE from the backends
@@ -806,9 +807,11 @@ promote_mode (const_tree type ATTRIBUTE_UNUSED, machine_mode mode,
     {
     case INTEGER_TYPE:   case ENUMERAL_TYPE:   case BOOLEAN_TYPE:
     case REAL_TYPE:      case OFFSET_TYPE:     case FIXED_POINT_TYPE:
-      PROMOTE_MODE (mode, unsignedp, type);
+      /* Values of these types always have scalar mode.  */
+      smode = as_a <scalar_mode> (mode);
+      PROMOTE_MODE (smode, unsignedp, type);
       *punsignedp = unsignedp;
-      return mode;
+      return smode;
 
 #ifdef POINTERS_EXTEND_UNSIGNED
     case REFERENCE_TYPE:
diff --git a/gcc/machmode.h b/gcc/machmode.h
index 5d84a2eca583ec7181bacfaecd2629f032cceef2..b3e79ca4df6850170269b1053e6cee82f099c394 100644
--- a/gcc/machmode.h
+++ b/gcc/machmode.h
@@ -650,7 +650,7 @@ extern machine_mode bitwise_mode_for_mode (machine_mode);
 /* Return a mode that is suitable for representing a vector,
    or BLKmode on failure.  */
 
-extern machine_mode mode_for_vector (machine_mode, unsigned);
+extern machine_mode mode_for_vector (scalar_mode, unsigned);
 
 /* A class for iterating through possible bitfield modes.  */
 class bit_field_mode_iterator
diff --git a/gcc/sdbout.c b/gcc/sdbout.c
index 8fcb97712172def20d28435e0df0501f7b738c71..acd25a3c7658eae14609fffabab9963da2d53965 100644
--- a/gcc/sdbout.c
+++ b/gcc/sdbout.c
@@ -1281,11 +1281,15 @@ sdbout_parms (tree parms)
 		   the parm with the variable's declared type, and adjust
 		   the address if the least significant bytes (which we are
 		   using) are not the first ones.  */
+		scalar_mode from_mode, to_mode;
 		if (BYTES_BIG_ENDIAN
-		    && TREE_TYPE (parms) != DECL_ARG_TYPE (parms))
-		  current_sym_value +=
-		    (GET_MODE_SIZE (TYPE_MODE (DECL_ARG_TYPE (parms)))
-		     - GET_MODE_SIZE (GET_MODE (DECL_RTL (parms))));
+		    && TREE_TYPE (parms) != DECL_ARG_TYPE (parms)
+		    && is_a <scalar_mode> (TYPE_MODE (DECL_ARG_TYPE (parms)),
+					   &from_mode)
+		    && is_a <scalar_mode> (GET_MODE (DECL_RTL (parms)),
+					   &to_mode))
+		  current_sym_value += (GET_MODE_SIZE (from_mode)
+					- GET_MODE_SIZE (to_mode));
 
 		if (MEM_P (DECL_RTL (parms))
 		    && GET_CODE (XEXP (DECL_RTL (parms), 0)) == PLUS
diff --git a/gcc/stor-layout.c b/gcc/stor-layout.c
index d6c1bb6e1f534278db164268b400156438521137..6414545d138aadb075385a595539c38aca444ea5 100644
--- a/gcc/stor-layout.c
+++ b/gcc/stor-layout.c
@@ -478,7 +478,7 @@ bitwise_type_for_mode (machine_mode mode)
    is no suitable mode.  */
 
 machine_mode
-mode_for_vector (machine_mode innermode, unsigned nunits)
+mode_for_vector (scalar_mode innermode, unsigned nunits)
 {
   machine_mode mode;