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WHEN EXPANSION
Goal:
reg r
wire w
when p1 :
w := b
r.init := x
when p2 :
w := c
r := d
r := e
==>
1. Remove last connect semantics
2. Remove conditional blocks
3. Eliminate concept of scoping
Exp | Value
--------------
r | e
w | mux(p1,mux(p2,c,b),null)
r.init | mux(p1,x,null)
==>
Symbolic Value - what can appear in value column
sv = e
| null
| svmux(e,sv1,sv2)
State:
{
r => void
r.init => p1
w => svmux(e,_,_)
}
==>
Build two tables, one mapping symbols to symbolic values, and another mapping symbols to declared types
if w is a wire:
merge {r=>x, w=>y} with {r=>x} under p : {r=>svmux(p,x,x), w=>y}
if s is a reg:
merge {r=>x,s=>y} with {r=>x} under p : {r=>svmux(p,x,x), s=>svmux(p,y,void)}
;this is to correctly calculate the ENABLE signal! when actually calculating the input, we will reduce it
;actually, since we will be doing the reducing anyways, we might as well not do anything different for wires,
; and instead do the reduction step separately
wire r {r=>VOID}
r := x {r=>x}
when p {r=>x}
reg s {r=>x,s=>VOID}
s := y {r=>x,s=>y}
wire w {r=>x,s=>y,w=>VOID}
else {r=>x}
reg s {r=>x,s=>VOID}
wire w {r=>x,s=>VOID,w=>VOID}
w := z {r=>x,s=>VOID,w=>z}
w := y {r=>x,s=>y,w=>y}
else
emptystmt {r=>x}
;merge table-c with table-a
;get unique keys of table-a + table-c
; (r,s,w)
{r=>(p?x:x),s=>(p?y:VOID),w=>(p?y:VOID)}
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