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dataflow -- do not consider the interprocedural case
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@nikomatsakis
nikomatsakis committed Feb 11, 2014
1 parent 6b8b751 commit 1bd7b18
Showing 1 changed file with 23 additions and 120 deletions.
143 changes: 23 additions & 120 deletions src/librustc/middle/dataflow.rs
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Expand Up @@ -17,7 +17,6 @@
*/


use std::cast;
use std::io;
use std::uint;
use std::vec;
Expand Down Expand Up @@ -72,9 +71,6 @@ pub trait DataFlowOperator {

/// Joins two predecessor bits together, typically either `|` or `&`
fn join(&self, succ: uint, pred: uint) -> uint;

/// True if we should propagate through closures
fn walk_closures(&self) -> bool;
}

struct PropagationContext<'a, O> {
Expand Down Expand Up @@ -373,8 +369,8 @@ impl<'a, O:DataFlowOperator> PropagationContext<'a, O> {
blk: &ast::Block,
in_out: &mut [uint],
loop_scopes: &mut ~[LoopScope]) {
debug!("DataFlowContext::walk_block(blk.id={:?}, in_out={})",
blk.id, bits_to_str(reslice(in_out)));
debug!("DataFlowContext::walk_block(blk.id={}, in_out={})",
blk.id, bits_to_str(in_out));

self.merge_with_entry_set(blk.id, in_out);

Expand Down Expand Up @@ -425,99 +421,12 @@ impl<'a, O:DataFlowOperator> PropagationContext<'a, O> {
in_out: &mut [uint],
loop_scopes: &mut ~[LoopScope]) {
debug!("DataFlowContext::walk_expr(expr={}, in_out={})",
expr.repr(self.dfcx.tcx), bits_to_str(reslice(in_out)));
expr.repr(self.dfcx.tcx), bits_to_str(in_out));

self.merge_with_entry_set(expr.id, in_out);

match expr.node {
ast::ExprFnBlock(ref decl, body) |
ast::ExprProc(ref decl, body) => {
if self.dfcx.oper.walk_closures() {
// In the absence of once fns, we must assume that
// every function body will execute more than
// once. Thus we treat every function body like a
// loop.
//
// What is subtle and a bit tricky, also, is how
// to deal with the "output" bits---that is, what
// do we consider to be the successor of a
// function body, given that it could be called
// from any point within its lifetime? What we do
// is to add their effects immediately as of the
// point of creation. Of course we have to ensure
// that this is sound for the analyses which make
// use of dataflow.
//
// In the case of the initedness checker (which
// does not currently use dataflow, but I hope to
// convert at some point), we will simply not walk
// closures at all, so it's a moot point.
//
// In the case of the borrow checker, this means
// the loans which would be created by calling a
// function come into effect immediately when the
// function is created. This is guaranteed to be
// earlier than the point at which the loan
// actually comes into scope (which is the point
// at which the closure is *called*). Because
// loans persist until the scope of the loans is
// exited, it is always a safe approximation to
// have a loan begin earlier than it actually will
// at runtime, so this should be sound.
//
// We stil have to be careful in the region
// checker and borrow checker to treat function
// bodies like loops, which implies some
// limitations. For example, a closure cannot root
// a managed box for longer than its body.
//
// General control flow looks like this:
//
// +- (expr) <----------+
// | | |
// | v |
// | (body) -----------+--> (exit)
// | | |
// | + (break/loop) -+
// | |
// +--------------------+
//
// This is a bit more conservative than a loop.
// Note that we must assume that even after a
// `break` occurs (e.g., in a `for` loop) that the
// closure may be reinvoked.
//
// One difference from other loops is that `loop`
// and `break` statements which target a closure
// both simply add to the `break_bits`.

// func_bits represents the state when the function
// returns
let mut func_bits = reslice(in_out).to_owned();

loop_scopes.push(LoopScope {
loop_id: expr.id,
break_bits: reslice(in_out).to_owned()
});
for input in decl.inputs.iter() {
self.walk_pat(input.pat, func_bits, loop_scopes);
}
self.walk_block(body, func_bits, loop_scopes);

// add the bits from any early return via `break`,
// `continue`, or `return` into `func_bits`
let loop_scope = loop_scopes.pop().unwrap();
join_bits(&self.dfcx.oper, loop_scope.break_bits, func_bits);

// add `func_bits` to the entry bits for `expr`,
// since we must assume the function may be called
// more than once
self.add_to_entry_set(expr.id, reslice(func_bits));

// the final exit bits include whatever was present
// in the original, joined with the bits from the function
join_bits(&self.dfcx.oper, func_bits, in_out);
}
ast::ExprFnBlock(..) | ast::ExprProc(..) => {
}

ast::ExprIf(cond, then, els) => {
Expand All @@ -536,7 +445,7 @@ impl<'a, O:DataFlowOperator> PropagationContext<'a, O> {
//
self.walk_expr(cond, in_out, loop_scopes);

let mut then_bits = reslice(in_out).to_owned();
let mut then_bits = in_out.to_owned();
self.walk_block(then, then_bits, loop_scopes);

self.walk_opt_expr(els, in_out, loop_scopes);
Expand All @@ -558,10 +467,10 @@ impl<'a, O:DataFlowOperator> PropagationContext<'a, O> {

self.walk_expr(cond, in_out, loop_scopes);

let mut body_bits = reslice(in_out).to_owned();
let mut body_bits = in_out.to_owned();
loop_scopes.push(LoopScope {
loop_id: expr.id,
break_bits: reslice(in_out).to_owned()
break_bits: in_out.to_owned()
});
self.walk_block(blk, body_bits, loop_scopes);
self.add_to_entry_set(expr.id, body_bits);
Expand All @@ -581,11 +490,11 @@ impl<'a, O:DataFlowOperator> PropagationContext<'a, O> {
// <--+ (break)
//

let mut body_bits = reslice(in_out).to_owned();
let mut body_bits = in_out.to_owned();
self.reset(in_out);
loop_scopes.push(LoopScope {
loop_id: expr.id,
break_bits: reslice(in_out).to_owned()
break_bits: in_out.to_owned()
});
self.walk_block(blk, body_bits, loop_scopes);
self.add_to_entry_set(expr.id, body_bits);
Expand All @@ -609,7 +518,7 @@ impl<'a, O:DataFlowOperator> PropagationContext<'a, O> {
//
self.walk_expr(discr, in_out, loop_scopes);

let mut guards = reslice(in_out).to_owned();
let mut guards = in_out.to_owned();

// We know that exactly one arm will be taken, so we
// can start out with a blank slate and just union
Expand All @@ -622,7 +531,7 @@ impl<'a, O:DataFlowOperator> PropagationContext<'a, O> {

// determine the bits for the body and then union
// them into `in_out`, which reflects all bodies to date
let mut body = reslice(guards).to_owned();
let mut body = guards.to_owned();
self.walk_pat_alternatives(arm.pats, body, loop_scopes);
self.walk_block(arm.body, body, loop_scopes);
join_bits(&self.dfcx.oper, body, in_out);
Expand All @@ -643,7 +552,7 @@ impl<'a, O:DataFlowOperator> PropagationContext<'a, O> {
ast::ExprAgain(label) => {
let scope = self.find_scope(expr, label, loop_scopes);
self.pop_scopes(expr, scope, in_out);
self.add_to_entry_set(scope.loop_id, reslice(in_out));
self.add_to_entry_set(scope.loop_id, in_out);
self.reset(in_out);
}

Expand Down Expand Up @@ -693,7 +602,7 @@ impl<'a, O:DataFlowOperator> PropagationContext<'a, O> {

ast::ExprBinary(_, op, l, r) if ast_util::lazy_binop(op) => {
self.walk_expr(l, in_out, loop_scopes);
let temp = reslice(in_out).to_owned();
let temp = in_out.to_owned();
self.walk_expr(r, in_out, loop_scopes);
join_bits(&self.dfcx.oper, temp, in_out);
}
Expand Down Expand Up @@ -756,7 +665,7 @@ impl<'a, O:DataFlowOperator> PropagationContext<'a, O> {

debug!("pop_scopes(from_expr={}, to_scope={:?}, in_out={})",
from_expr.repr(tcx), to_scope.loop_id,
bits_to_str(reslice(in_out)));
bits_to_str(in_out));

let mut id = from_expr.id;
while id != to_scope.loop_id {
Expand All @@ -781,11 +690,11 @@ impl<'a, O:DataFlowOperator> PropagationContext<'a, O> {
in_out: &mut [uint]) {
self.pop_scopes(from_expr, to_scope, in_out);
self.dfcx.apply_kill(from_expr.id, in_out);
join_bits(&self.dfcx.oper, reslice(in_out), to_scope.break_bits);
debug!("break_from_to(from_expr={}, to_scope={:?}) final break_bits={}",
join_bits(&self.dfcx.oper, in_out, to_scope.break_bits);
debug!("break_from_to(from_expr={}, to_scope={}) final break_bits={}",
from_expr.repr(self.tcx()),
to_scope.loop_id,
bits_to_str(reslice(in_out)));
bits_to_str(in_out));
}

fn walk_exprs(&mut self,
Expand Down Expand Up @@ -830,10 +739,10 @@ impl<'a, O:DataFlowOperator> PropagationContext<'a, O> {
in_out: &mut [uint],
_loop_scopes: &mut ~[LoopScope]) {
debug!("DataFlowContext::walk_pat(pat={}, in_out={})",
pat.repr(self.dfcx.tcx), bits_to_str(reslice(in_out)));
pat.repr(self.dfcx.tcx), bits_to_str(in_out));

ast_util::walk_pat(pat, |p| {
debug!(" p.id={:?} in_out={}", p.id, bits_to_str(reslice(in_out)));
debug!(" p.id={} in_out={}", p.id, bits_to_str(in_out));
self.merge_with_entry_set(p.id, in_out);
self.dfcx.apply_gen_kill(p.id, in_out);
true
Expand All @@ -852,7 +761,7 @@ impl<'a, O:DataFlowOperator> PropagationContext<'a, O> {
// In the general case, the patterns in `pats` are
// alternatives, so we must treat this like an N-way select
// statement.
let initial_state = reslice(in_out).to_owned();
let initial_state = in_out.to_owned();
for &pat in pats.iter() {
let mut temp = initial_state.clone();
self.walk_pat(pat, temp, loop_scopes);
Expand Down Expand Up @@ -929,8 +838,8 @@ impl<'a, O:DataFlowOperator> PropagationContext<'a, O> {
let (start, end) = self.dfcx.compute_id_range(id);
let changed = { // FIXME(#5074) awkward construction
let on_entry = self.dfcx.on_entry.mut_slice(start, end);
let changed = join_bits(&self.dfcx.oper, reslice(pred_bits), on_entry);
copy_bits(reslice(on_entry), pred_bits);
let changed = join_bits(&self.dfcx.oper, pred_bits, on_entry);
copy_bits(on_entry, pred_bits);
changed
};
if changed {
Expand All @@ -942,7 +851,7 @@ impl<'a, O:DataFlowOperator> PropagationContext<'a, O> {
}

fn mut_bits_to_str(words: &mut [uint]) -> ~str {
bits_to_str(reslice(words))
bits_to_str(words)
}

fn bits_to_str(words: &[uint]) -> ~str {
Expand Down Expand Up @@ -1007,9 +916,3 @@ fn bit_str(bit: uint) -> ~str {
format!("[{}:{}-{:02x}]", bit, byte, lobits)
}

fn reslice<'a>(v: &'a mut [uint]) -> &'a [uint] {
// bFIXME(#5074) this function should not be necessary at all
unsafe {
cast::transmute(v)
}
}

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