incr.comp.: Hide concrete hash algorithm used for ICH

src/librustc/session/mod.rs

@@ -118,6 +118,8 @@ pub struct PerfStats {
     pub incr_comp_hashes_time: Cell<Duration>,
     // The number of incr. comp. hash computations performed
     pub incr_comp_hashes_count: Cell<u64>,
+    // The number of bytes hashed when computing ICH values
+    pub incr_comp_bytes_hashed: Cell<u64>,
     // The accumulated time spent on computing symbol hashes
     pub symbol_hash_time: Cell<Duration>,
 }
@@ -439,6 +441,11 @@ impl Session {
                  duration_to_secs_str(self.perf_stats.incr_comp_hashes_time.get()));
         println!("Total number of incr. comp. hashes computed:   {}",
                  self.perf_stats.incr_comp_hashes_count.get());
+        println!("Total number of bytes hashed for incr. comp.:  {}",
+                 self.perf_stats.incr_comp_bytes_hashed.get());
+        println!("Average bytes hashed per incr. comp. HIR node: {}",
+                 self.perf_stats.incr_comp_bytes_hashed.get() /
+                 self.perf_stats.incr_comp_hashes_count.get());
         println!("Total time spent computing symbol hashes:      {}",
                  duration_to_secs_str(self.perf_stats.symbol_hash_time.get()));
     }
@@ -571,6 +578,7 @@ pub fn build_session_(sopts: config::Options,
             svh_time: Cell::new(Duration::from_secs(0)),
             incr_comp_hashes_time: Cell::new(Duration::from_secs(0)),
             incr_comp_hashes_count: Cell::new(0),
+            incr_comp_bytes_hashed: Cell::new(0),
             symbol_hash_time: Cell::new(Duration::from_secs(0)),
         }
     };

src/librustc_incremental/calculate_svh/hasher.rs

@@ -0,0 +1,46 @@
+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use std::hash::Hasher;
+use std::collections::hash_map::DefaultHasher;
+
+#[derive(Debug)]
+pub struct IchHasher {
+    // FIXME: this should use SHA1, not DefaultHasher. DefaultHasher is not
+    // built to avoid collisions.
+    state: DefaultHasher,
+    bytes_hashed: u64,
+}
+
+impl IchHasher {
+    pub fn new() -> IchHasher {
+        IchHasher {
+            state: DefaultHasher::new(),
+            bytes_hashed: 0
+        }
+    }
+
+    pub fn bytes_hashed(&self) -> u64 {
+        self.bytes_hashed
+    }
+}
+
+impl Hasher for IchHasher {
+    #[inline]
+    fn finish(&self) -> u64 {
+        self.state.finish()
+    }
+
+    #[inline]
+    fn write(&mut self, bytes: &[u8]) {
+        self.state.write(bytes);
+        self.bytes_hashed += bytes.len() as u64;
+    }
+}

src/librustc_incremental/calculate_svh/mod.rs

@@ -30,7 +30,6 @@
 use syntax::ast;
 use std::cell::RefCell;
 use std::hash::{Hash, Hasher};
-use std::collections::hash_map::DefaultHasher;
 use rustc::dep_graph::DepNode;
 use rustc::hir;
 use rustc::hir::def_id::{CRATE_DEF_INDEX, DefId};
@@ -43,10 +42,12 @@ use rustc::session::config::DebugInfoLevel::NoDebugInfo;
 use self::def_path_hash::DefPathHashes;
 use self::svh_visitor::StrictVersionHashVisitor;
 use self::caching_codemap_view::CachingCodemapView;
+use self::hasher::IchHasher;
 
 mod def_path_hash;
 mod svh_visitor;
 mod caching_codemap_view;
+mod hasher;
 
 pub struct IncrementalHashesMap {
     hashes: FnvHashMap<DepNode<DefId>, u64>,
@@ -74,6 +75,10 @@ impl IncrementalHashesMap {
     pub fn iter<'a>(&'a self) -> ::std::collections::hash_map::Iter<'a, DepNode<DefId>, u64> {
         self.hashes.iter()
     }
+
+    pub fn len(&self) -> usize {
+        self.hashes.len()
+    }
 }
 
 impl<'a> ::std::ops::Index<&'a DepNode<DefId>> for IncrementalHashesMap {
@@ -102,6 +107,9 @@ pub fn compute_incremental_hashes_map<'a, 'tcx: 'a>(tcx: TyCtxt<'a, 'tcx, 'tcx>)
                                  |v| visit::walk_crate(v, krate));
         krate.visit_all_items(&mut visitor);
     });
+
+    tcx.sess.perf_stats.incr_comp_hashes_count.set(visitor.hashes.len() as u64);
+
     record_time(&tcx.sess.perf_stats.svh_time, || visitor.compute_crate_hash());
     visitor.hashes
 }
@@ -127,9 +135,7 @@ impl<'a, 'tcx> HashItemsVisitor<'a, 'tcx> {
     {
         assert!(def_id.is_local());
         debug!("HashItemsVisitor::calculate(def_id={:?})", def_id);
-        // FIXME: this should use SHA1, not DefaultHasher. DefaultHasher is not
-        // built to avoid collisions.
-        let mut state = DefaultHasher::new();
+        let mut state = IchHasher::new();
         walk_op(&mut StrictVersionHashVisitor::new(&mut state,
                                                    self.tcx,
                                                    &mut self.def_path_hashes,
@@ -138,12 +144,16 @@ impl<'a, 'tcx> HashItemsVisitor<'a, 'tcx> {
         let item_hash = state.finish();
         self.hashes.insert(DepNode::Hir(def_id), item_hash);
         debug!("calculate_item_hash: def_id={:?} hash={:?}", def_id, item_hash);
+
+        let bytes_hashed = self.tcx.sess.perf_stats.incr_comp_bytes_hashed.get() +
+                           state.bytes_hashed();
+        self.tcx.sess.perf_stats.incr_comp_bytes_hashed.set(bytes_hashed);
     }
 
     fn compute_crate_hash(&mut self) {
         let krate = self.tcx.map.krate();
 
-        let mut crate_state = DefaultHasher::new();
+        let mut crate_state = IchHasher::new();
 
         let crate_disambiguator = self.tcx.sess.local_crate_disambiguator();
         "crate_disambiguator".hash(&mut crate_state);

src/librustc_incremental/calculate_svh/svh_visitor.rs

@@ -31,10 +31,10 @@ use rustc::hir::intravisit as visit;
 use rustc::ty::TyCtxt;
 use rustc_data_structures::fnv;
 use std::hash::Hash;
-use std::collections::hash_map::DefaultHasher;
 
 use super::def_path_hash::DefPathHashes;
 use super::caching_codemap_view::CachingCodemapView;
+use super::hasher::IchHasher;
 
 const IGNORED_ATTRIBUTES: &'static [&'static str] = &[
     "cfg",
@@ -48,7 +48,7 @@ const IGNORED_ATTRIBUTES: &'static [&'static str] = &[
 
 pub struct StrictVersionHashVisitor<'a, 'hash: 'a, 'tcx: 'hash> {
     pub tcx: TyCtxt<'hash, 'tcx, 'tcx>,
-    pub st: &'a mut DefaultHasher,
+    pub st: &'a mut IchHasher,
     // collect a deterministic hash of def-ids that we have seen
     def_path_hashes: &'a mut DefPathHashes<'hash, 'tcx>,
     hash_spans: bool,
@@ -56,7 +56,7 @@ pub struct StrictVersionHashVisitor<'a, 'hash: 'a, 'tcx: 'hash> {
 }
 
 impl<'a, 'hash, 'tcx> StrictVersionHashVisitor<'a, 'hash, 'tcx> {
-    pub fn new(st: &'a mut DefaultHasher,
+    pub fn new(st: &'a mut IchHasher,
                tcx: TyCtxt<'hash, 'tcx, 'tcx>,
                def_path_hashes: &'a mut DefPathHashes<'hash, 'tcx>,
                codemap: &'a mut CachingCodemapView<'tcx>,