* doc/rtl.texi (const_double): Document as sign-extending.
* expmed.c (expand_mult): Ensure we don't use shift
incorrectly.
* emit-rtl.c (immed_double_int_const): Refine to state the
value is signed.
* simplify-rtx.c (mode_signbit_p): Add a fixme for wider than
CONST_DOUBLE integers.
(simplify_const_unary_operation, UNSIGNED_FLOAT): Ensure no
negative values are converted. Fix conversions bigger than
HOST_BITS_PER_WIDE_INT.
(simplify_binary_operation_1): Ensure we don't use shift
incorrectly.
(simplify_immed_subreg): Sign-extend CONST_DOUBLEs.
* explow.c (plus_constant_mode): Add.
(plus_constant): Implement with plus_constant_mode.
* rtl.h (plus_constant_mode): Add.
From-SVN: r186147
