Unify phony assignment into assignment

But now we have an "updating assignment" for the original concept
of an assignment

wgsl/index.bs

@@ -4829,19 +4829,29 @@ compound_statement
 
 ## Assignment Statement ## {#assignment}
 
-An <dfn noexport dfn-for="statement">assignment</dfn> statement replaces the contents of a variable,
-or a portion of a variable, with a new value.
+An <dfn noexport dfn-for="statement">assignment</dfn> evaluates an expression,
+and optionally stores it in memory (thus updating the contents of a variable).
 
-The
-expression to the left of the equals token is the <dfn noexport>left-hand side</dfn>,
+<pre class='def'>
+assignment_statement
+  : (unary_expression | UNDERSCORE) EQUAL short_circuit_or_expression
+</pre>
+
+
+The text to the left of the equals token is the <dfn noexport>left-hand side</dfn>,
 and the
 expression to the right of the equals token is the <dfn noexport>right-hand side</dfn>.
 
+### Updating Assignment ### {#updating-assignment-section}
+
+When the [=left-hand side=] of an assignment is an expression, the assignment is an <dfn noexport>updating assignment</dfn>:
+The value of the right-hand side is written to the memory referenced by the left-hand side.
+
 <table class='data'>
   <thead>
     <tr><th style="width:40%">Precondition<th>Statement<th>Description
   </thead>
-  <tr algorithm="assignment">
+  <tr algorithm="updating assignment">
     <td>|r|: ref<|SC|,|T|,|A|>,<br>
         |A| is [=access/write=] or [=access/read_write=]<br>
         |e|: |T|,<br>
@@ -4858,8 +4868,8 @@ expression to the right of the equals token is the <dfn noexport>right-hand side
         (OpStore)
 </table>
 
-In the simplest case, the left hand side of the assignment statement is the
-name of a variable.  See [[#forming-references-and-pointers]] for other cases.
+In the simplest case, the left hand side is the name of a variable.
+See [[#forming-references-and-pointers]] for other cases.
 
     <div class='example wgsl' heading='Assignments'>
       <xmp highlight='rust'>
@@ -4888,18 +4898,11 @@ name of a variable.  See [[#forming-references-and-pointers]] for other cases.
       </xmp>
     </div>
 
-<pre class='def'>
-assignment_statement
-  : unary_expression EQUAL short_circuit_or_expression
-      If unary_expression is a variable, this maps to OpStore to the variable.
-      Otherwise, unary expression is a pointer expression in an Assigning (L-value) context
-      which maps to OpAccessChain followed by OpStore
-</pre>
+### Phony Assignment ### {#phony-assignment-section}
 
-## Phony-Assignment Statement ## {#phony-assignment-statement}
-
-A <dfn dfn-for="statement" noexport>phony-assignment</dfn> statement evaluates an expression,
-and does nothing with the resulting value.
+When the [=left-hand side=] of an assignment is an underscore token,
+the assignment is an <dfn noexport>phony assignment</dfn>:
+The right-hand side is evaluated, and then ignored.
 
 <table class='data'>
   <thead>
@@ -4918,7 +4921,8 @@ and does nothing with the resulting value.
 A phony-assignment is useful for:
 * Calling a function that returns a value, but clearly expressing that the resulting value
     is not needed.
-* Establishing a particular variable as part of the [=resource interface of a shader|shader's resource interface=].
+* [=statically accessed|Statically accessing=] a variable, thus establishing it as a part of
+    the [=resource interface of a shader|shader's resource interface=].
 
     Note: A variable's store type may not be constructible, e.g. it contains an atomic type, or a runtime-sized array.
     In these cases, use a pointer to the variable's contents instead.
@@ -4963,12 +4967,6 @@ A phony-assignment is useful for:
   </xmp>
 </div>
 
-<pre class='def'>
-phony_assignment_statement
-  : UNDERSCORE EQUAL short_circuit_or_expression
-</pre>
-
-
 ## Control flow TODO ## {#control-flow}
 
 ### Sequence TODO ### {#sequence-statement}
@@ -5162,9 +5160,9 @@ for_statement
   : FOR PAREN_LEFT for_header PAREN_RIGHT compound_statement
 
 for_header
-  : (variable_statement | assignment_statement | phony_assignment_statement | func_call_statement)? SEMICOLON
+  : (variable_statement | assignment_statement | func_call_statement)? SEMICOLON
      short_circuit_or_expression? SEMICOLON
-     (assignment_statement | phony_assignment_statement | func_call_statement)?
+     (assignment_statement | func_call_statement)?
 </pre>
 
 The <dfn dfn-for="statement">for</dfn> statement takes the form
@@ -5453,7 +5451,6 @@ statement
   | continue_statement SEMICOLON
   | DISCARD SEMICOLON
   | assignment_statement SEMICOLON
-  | phony_assignment_statement SEMICOLON
   | compound_statement
 </pre>