Merge 2017-07 CWG Motion 1

Author: zygoloid

source/basic.tex

@@ -3564,7 +3564,10 @@
 \indextext{representation!value}%
 \defn{value representation}
 of an object is the set of bits that hold
-the value of type \tcode{T}. For trivially copyable types, the value representation is
+the value of type \tcode{T}.
+Bits in the object representation that are not part of the value representation
+are \defn{padding bits}.
+For trivially copyable types, the value representation is
 a set of bits in the object representation that determines a
 \defn{value}, which is one discrete element of an
 \impldef{values of a trivially copyable type} set of values.\footnote{The
@@ -3731,7 +3734,7 @@
 \begin{note}
 A bit-field of narrow character type whose length is larger than
 the number of bits in the object representation of that type has
-padding bits; see~\ref{class.bit}.
+padding bits; see~\ref{basic.types}.
 \end{note}
 For unsigned narrow
 character types, each possible bit pattern of the value representation

source/classes.tex

@@ -1306,8 +1306,7 @@
 value of the integral constant expression may
 be larger than the number of bits in the object
 representation~(\ref{basic.types}) of the bit-field's type; in such
-cases the extra bits are used as padding bits and do not participate in
-the value representation~(\ref{basic.types}) of the bit-field.
+cases the extra bits are padding bits~(\ref{basic.types}).
 \indextext{allocation!implementation-defined bit-field}%
 Allocation of bit-fields within a class object is
 \impldef{allocation of bit-fields within a class object}.

source/declarators.tex

@@ -2497,20 +2497,22 @@
 if
 \tcode{T}
 is a (possibly cv-qualified) non-union class type,
+its padding bits~(\ref{basic.types}) are initialized to zero bits and
 each non-static data member,
 each non-virtual base class subobject, and,
 if the object is not a base class subobject,
 each virtual base class subobject
-is zero-initialized and padding is initialized to zero bits;
+is zero-initialized;
 
 \item
 if
 \tcode{T}
 is a (possibly cv-qualified) union type,
+its padding bits~(\ref{basic.types}) are initialized to zero bits and
 the
 object's first non-static named
 data member
-is zero-initialized and padding is initialized to zero bits;
+is zero-initialized;
 
 \item
 if