Add op= assignments

Signed-off-by: Chris Dodd <[email protected]>

p4-16/spec/P4-16-spec.adoc

@@ -5498,6 +5498,15 @@ types (e.g. ``struct``s) are copied recursively, and all components
 of ``header``s are copied, including "validity" bits. Assignment is
 not defined for `extern` values.
 
+An assignment may also be written with a binary arithmetic or bit manipulation
+operator immediately before the `=` sign.  This performs the binary operator on
+the old value of the left sub-expression and the right sub-expression and assigns
+the result to the l-value.  Thus an assignment like `A += B` is equivalent
+to `A = A + B`, except that `A` is only evaluated once.  This means that
+any side-effects within this operand (eg, a function call inside an array index
+or slice expression) only occur once.  This is not valid
+for comparison operators, logical operators, concat, range, or mask operators.
+
 [#sec-empty-stmt]
 === Empty statement
 

p4-16/spec/grammar.adoc

@@ -736,7 +736,19 @@ typedefDeclaration
 assignmentOrMethodCallStatement
     : lvalue "(" argumentList ")" ";"
     | lvalue "<" typeArgumentList ">" "(" argumentList ")" ";"
-    | lvalue "="  expression ";"
+    | lvalue "=" expression ";"
+    | lvalue "*=" expression ";"
+    | lvalue "/=" expression ";"
+    | lvalue "%=" expression ";"
+    | lvalue "+=" expression ";"
+    | lvalue "-=" expression ";"
+    | lvalue "|+|=" expression ";"
+    | lvalue "|-|=" expression ";"
+    | lvalue "<<=" expression ";"
+    | lvalue ">>=" expression ";"
+    | lvalue "&=" expression ";"
+    | lvalue "|=" expression ";"
+    | lvalue "^=" expression ";"
     ;
 // end::assignmentOrMethodCallStatement[]