1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
use proc_macro::TokenStream;
use proc_macro2::Span;
use quote::{format_ident, quote};
use std::borrow::BorrowMut;
use std::collections::BTreeSet;
use syn::export::ToTokens;
use syn::visit_mut::VisitMut;
use syn::{Block, Expr, Pat, PatIdent, PatType, Stmt};
mod attr_parser;
#[proc_macro_attribute]
pub fn hoist_temporaries(attr: TokenStream, item: TokenStream) -> TokenStream {
if !attr.is_empty() {
panic!("Invalid attribute - hoist_temporaries takes no arguments.");
}
let mut idents = BTreeSet::new();
let stripped_item = attr_parser::parse(item, &mut idents)
.map_err(|err| {
panic!(
"Failed to parse function marked with #[hoist_temporaries::hoist_temporaries]: {}",
err
)
})
.unwrap();
let mut f = syn::parse::<syn::ItemFn>(stripped_item)
.map_err(|err| panic!("Failed to parse function: {}", err))
.unwrap();
for ident in idents {
let mut rewrite_visitor = RewriteAssignmentVisitor {
ident: ident.to_string(),
did_rewrite: false,
};
rewrite_visitor.visit_item_fn_mut(&mut f);
if rewrite_visitor.did_rewrite {
CreateBackingVisitor {
ident: ident.to_string(),
}
.visit_item_fn_mut(&mut f);
} else {
eprintln!("warning: hoist_temporaries was enabled for variable `{}` on function `{}` but no temporaries were hoisted.", ident, f.sig.ident);
}
}
f.into_token_stream().into()
}
fn backing_ident(ident: &str) -> proc_macro2::Ident {
format_ident!("__hoist_temporaries_backing_variable_{}", ident)
}
struct CreateBackingVisitor {
ident: String,
}
impl VisitMut for CreateBackingVisitor {
fn visit_block_mut(&mut self, block: &mut Block) {
self.create_backing_variable(block);
syn::visit_mut::visit_block_mut(self, block)
}
}
impl CreateBackingVisitor {
fn create_backing_variable(&self, block: &mut Block) {
let pos = block.stmts.iter().position(|stmt| {
if let Stmt::Local(local) = stmt {
if let Pat::Ident(PatIdent { ident, .. }) = &local.pat {
return *ident == self.ident;
} else if let Pat::Type(PatType { pat, .. }) = &local.pat {
if let Pat::Ident(PatIdent { ident, .. }) = pat.as_ref() {
return *ident == self.ident;
}
}
}
false
});
if let Some(pos) = pos {
let backing_ident = backing_ident(&self.ident);
block.stmts.insert(
pos,
syn::parse2::<syn::Stmt>(quote! { let mut #backing_ident; })
.expect("Could not parse code generated by the procedural macro"),
);
}
}
}
struct RewriteAssignmentVisitor {
ident: String,
did_rewrite: bool,
}
impl VisitMut for RewriteAssignmentVisitor {
fn visit_block_mut(&mut self, block: &mut Block) {
self.rewrite_assignments(block);
syn::visit_mut::visit_block_mut(self, block)
}
}
impl RewriteAssignmentVisitor {
fn rewrite_assignments(&mut self, block: &mut Block) {
let stmts = std::mem::replace(&mut block.stmts, vec![]);
block.stmts = stmts
.into_iter()
.flat_map(|mut stmt| {
if let Stmt::Semi(Expr::Assign(assign), _) = &mut stmt {
if let Expr::Path(path) = assign.left.borrow_mut() {
if let Some(ident) = path.path.get_ident() {
if *ident == self.ident {
if let Expr::Reference(rhs) = assign.right.borrow_mut() {
self.did_rewrite = true;
let backing_ident = backing_ident(&self.ident);
assign.left = Box::new(Expr::Path(
syn::parse2::<syn::ExprPath>(quote! { #backing_ident })
.expect("Could not parse code generated by the procedural macro"),
));
assign.right = rhs.expr.clone();
let ident =
proc_macro2::Ident::new(&self.ident, Span::call_site());
let new_stmt = syn::parse2::<syn::Stmt>(
quote! { #ident = &#backing_ident;},
)
.expect("Could not parse code generated by the procedural macro");
return vec![stmt, new_stmt];
}
}
}
}
}
vec![stmt]
})
.collect();
}
}