Expression-sizing
Calculate the widths and types of expressions.
Expression sizing and typing is possibly the most complex,
error-prone, and subtle aspect of processing Verilog expressions. One
reason for this is that the size and signedness of subexpressions depends upon
the other terms in the expressions that contain them. For instance, the result
of ((4'd14 + 4'd3) >> 4'd1) might be either 8 or 0, depending on where it
is being used. Another reason is just how elaborate the rules for sizing are,
and how many corner cases there are.
These issues mean that great care must be taken even when writing
simple-looking reductions like constant folding. Moreover, you really need to
understand how sizing works if you are going to safely write any code that
generates Verilog expressions.
I have put together a gentle expression-sizing-intro which describes
Verilog's basic algorithm for how sizes and types are determined. You may also
wish to familiarize yourself with the VL notion of well-typed expressions.
The expression-sizing transformation attempts to determine expression sizes
and types throughout a module. Prerequisite transformations:
BOZO follow-hids might also be a prerequisite when we add support for
HIDs.
It is valid to run this transformation any time after the above transforms
have been run. It is also "idempotent," so it is perfectly valid to run the
transform more than once on the same module (e.g., perhaps your subsequent
transformation wishes to add some assignment statements, and subsequently wants
to determine their sizes.
Subtopics
- Expression-sizing-minutia
- Specific issues and questions related to the expression sizing and
typing of expressions.
- Expression-sizing-intro
- Introduction to Verilog's expression sizing/typing algorithm.
- Vl-keyvalue-pattern-collect-array-replacements
- Vl-assignpattern-positional-replacement
- Return the list of type/expression pairs to concatenate together to
replace a positional assignment pattern.
- Vl-plainarg-exprsize
- Compute sizes and types of expressions throughout a vl-plainarg-p
- Vl-assignpattern-keyvalue-replacement
- Return the list of type/expression pairs to concatenate together to
replace a key/value assignment pattern.
- Vl-keyvalue-pattern-collect-struct-replacements
- Vl-modulelist-exprsize
- (vl-modulelist-exprsize x ss) maps vl-module-exprsize across a list.
- Vl-expr-assignpattern-extend/truncate
- Vl-structmemberlist->types
- (vl-structmemberlist->types x) maps vl-structmember->type across a list.
- Vl-expr-size
- Determine sizes for a top-level or self-determined expression.
- Vl-expr-selfdetermine-type
- Determine the (unpacked) type of an expression.
- Vl-assignpattern-multi-replacement
- Return the list of type/expression pairs to concatenate together to
replace a positional assignment pattern.
- Vl-parse-keyval-pattern-struct
- Vl-plainarglist-exprsize
- Compute sizes and types of expressions throughout a vl-plainarglist-p.
- Vl-parse-keyval-pattern-array
- Vl-warn-about-implicit-extension
- Lint-like warnings about right hand sides being extended.
- Vl-assigncontext-size
- Vl-arguments-exprsize
- Compute sizes and types of expressions throughout a vl-arguments-p
- Vl-assignpattern-replacement
- Vl-packeddimensionlist-exprsize
- Compute sizes and types of expressions throughout a vl-packeddimensionlist-p.
- Vl-namedparamvaluelist-exprsize
- Compute sizes and types of expressions throughout a vl-namedparamvaluelist-p.
- Vl-maybe-delayoreventcontrol-exprsize
- Compute sizes and types of expressions throughout a vl-maybe-delayoreventcontrol-p
- Vl-repeateventcontrol-exprsize
- Compute sizes and types of expressions throughout a vl-repeateventcontrol-p
- Vl-paramvaluelist-exprsize
- Compute sizes and types of expressions throughout a vl-paramvaluelist-p.
- Vl-maybe-packeddimension-exprsize
- Compute sizes and types of expressions throughout a vl-maybe-packeddimension-p
- Vl-delayoreventcontrol-exprsize
- Compute sizes and types of expressions throughout a vl-delayoreventcontrol-p
- Vl-namedparamvalue-exprsize
- Compute sizes and types of expressions throughout a vl-namedparamvalue-p
- Vl-namedarglist-exprsize
- Compute sizes and types of expressions throughout a vl-namedarglist-p.
- Vl-enumitemlist-exprsize
- Compute sizes and types of expressions throughout a vl-enumitemlist-p.
- Vl-packeddimension-exprsize
- Compute sizes and types of expressions throughout a vl-packeddimension-p
- Vl-maybe-paramvalue-exprsize
- Compute sizes and types of expressions throughout a vl-maybe-paramvalue-p
- Vl-evatomlist-exprsize
- Compute sizes and types of expressions throughout a vl-evatomlist-p.
- Vl-atom-selfdetermine-type
- Vl-rangelist-exprsize
- Compute sizes and types of expressions throughout a vl-rangelist-p.
- Vl-maybe-gatedelay-exprsize
- Compute sizes and types of expressions throughout a vl-maybe-gatedelay-p
- Vl-maybe-datatype-exprsize
- Compute sizes and types of expressions throughout a vl-maybe-datatype-p
- Vl-gatedelay-exprsize
- Compute sizes and types of expressions throughout a vl-gatedelay-p
- Vl-paramargs-exprsize
- Compute sizes and types of expressions throughout a vl-paramargs-p
- Vl-namedarg-exprsize
- Compute sizes and types of expressions throughout a vl-namedarg-p
- Vl-eventcontrol-exprsize
- Compute sizes and types of expressions throughout a vl-eventcontrol-p
- Vl-enumbasetype-exprsize
- Compute sizes and types of expressions throughout a vl-enumbasetype-p
- Vl-delaycontrol-exprsize
- Compute sizes and types of expressions throughout a vl-delaycontrol-p
- Vl-paramvalue-exprsize
- Compute sizes and types of expressions throughout a vl-paramvalue-p
- Vl-maybe-range-exprsize
- Compute sizes and types of expressions throughout a vl-maybe-range-p
- Vl-enumitem-exprsize
- Compute sizes and types of expressions throughout a vl-enumitem-p
- Vl-range-exprsize
- Compute sizes and types of expressions throughout a vl-range-p
- Vl-paramdecl-exprsize
- Compute sizes and types of expressions throughout a vl-paramdecl-p
- Vl-paramdecllist-exprsize
- Compute sizes and types of expressions throughout a vl-paramdecllist-p.
- Vl-maybe-expr-size
- Compute sizes and types of expressions throughout a vl-maybe-expr-p
- Vl-evatom-exprsize
- Compute sizes and types of expressions throughout a vl-evatom-p
- Vl-vardecllist-exprsize
- Compute sizes and types of expressions throughout a vl-vardecllist-p.
- Vl-portdecllist-exprsize
- Compute sizes and types of expressions throughout a vl-portdecllist-p.
- Vl-modinstlist-exprsize
- Compute sizes and types of expressions throughout a vl-modinstlist-p.
- Vl-initiallist-exprsize
- Compute sizes and types of expressions throughout a vl-initiallist-p.
- Vl-gateinstlist-exprsize
- Compute sizes and types of expressions throughout a vl-gateinstlist-p.
- Vl-fundecllist-exprsize
- Compute sizes and types of expressions throughout a vl-fundecllist-p.
- Vl-assign-exprsize
- Compute sizes and types of expressions throughout a vl-assign-p
- Vl-interfaceport-exprsize
- Compute sizes and types of expressions throughout a vl-interfaceport-p
- Vl-assignlist-exprsize
- Compute sizes and types of expressions throughout a vl-assignlist-p.
- Vl-alwayslist-exprsize
- Compute sizes and types of expressions throughout a vl-alwayslist-p.
- Vl-portlist-exprsize
- Compute sizes and types of expressions throughout a vl-portlist-p.
- Vl-modinst-exprsize
- Compute sizes and types of expressions throughout a vl-modinst-p
- Vl-gateinst-exprsize
- Compute sizes and types of expressions throughout a vl-gateinst-p
- Vl-fundecl-exprsize
- Compute sizes and types of expressions throughout a vl-fundecl-p
- Vl-vardecl-exprsize
- Compute sizes and types of expressions throughout a vl-vardecl-p
- Vl-regularport-exprsize
- Compute sizes and types of expressions throughout a vl-regularport-p
- Vl-portdecl-exprsize
- Compute sizes and types of expressions throughout a vl-portdecl-p
- Vl-initial-exprsize
- Compute sizes and types of expressions throughout a vl-initial-p
- Vl-always-exprsize
- Compute sizes and types of expressions throughout a vl-always-p
- Vl-port-exprsize
- Compute sizes and types of expressions throughout a vl-port-p
- Vl-lvalue-type
- Vl-classify-extension-warning-hook
- Configurable hook for classifying extension warnings.
- Welltyped
- Expressions whose sizes and types are sensible.
- Vl-castexpr->datatype
- Vl-expr-size-assigncontext
- Size and resolve assignment patterns in an expression, given the type of its LHS.
- Vl-type-expr-pairs-sum-datatype-sizes
- Vl-basictype->datatype
- Vl-expr-replace-assignpatterns
- Rewrite an expression to replace assignment patterns with concatenations.
- Vl-design-exprsize
- Top-level expression-sizing transform.
- Vl-op-simple-vector-p
- Vl-expr-val-alist-max-count
- Vl-expr-has-patterns
- Vl-exprlist-max-count
- Vl-unsigned-when-size-zero-lst
- Vl-type-expr-pairs
- An alist mapping vl-datatype-p to vl-expr-p.
- Append-n
- Vl-expr-val-alist
- An alist mapping anything to vl-expr-p.
- Vl-datatypelist
- A list of vl-datatype-p objects.
