As-applied.  From:

https://gcc.gnu.org/ml/gcc-patches/2014-10/msg02605.html

Linked from bug62231 comment 4 there

---
 gcc/config/rs6000/rs6000.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/gcc/config/rs6000/rs6000.c
+++ b/gcc/config/rs6000/rs6000.c
@@ -1677,7 +1677,7 @@
      SCmode so as to pass the value correctly in a pair of
      registers.  */
   else if (TARGET_E500_DOUBLE && FLOAT_MODE_P (mode) && mode != SCmode
-	   && !DECIMAL_FLOAT_MODE_P (mode))
+	   && !DECIMAL_FLOAT_MODE_P (mode) && SPE_SIMD_REGNO_P (regno))
     reg_size = UNITS_PER_FP_WORD;
 
   else