Rollup merge of #51982 - michaelwoerister:hash-modules-properly, r=nikomatsakis

incr.comp.: Take names of children into account when computing the ICH of a module's HIR.

Fixes #40876. Red-green tracking does not make this a problem anymore. We should verify this via a perf-run though.

r? @nikomatsakis

src/librustc/hir/map/definitions.rs

@@ -23,6 +23,7 @@ use rustc_data_structures::indexed_vec::{IndexVec};
 use rustc_data_structures::stable_hasher::StableHasher;
 use serialize::{Encodable, Decodable, Encoder, Decoder};
 use session::CrateDisambiguator;
+use std::borrow::Borrow;
 use std::fmt::Write;
 use std::hash::Hash;
 use syntax::ast;
@@ -389,6 +390,13 @@ pub struct DefPathHash(pub Fingerprint);
 
 impl_stable_hash_for!(tuple_struct DefPathHash { fingerprint });
 
+impl Borrow<Fingerprint> for DefPathHash {
+    #[inline]
+    fn borrow(&self) -> &Fingerprint {
+        &self.0
+    }
+}
+
 impl Definitions {
     /// Create new empty definition map.
     pub fn new() -> Definitions {

src/librustc/ich/fingerprint.rs

@@ -45,6 +45,18 @@ impl Fingerprint {
         )
     }
 
+    // Combines two hashes in an order independent way. Make sure this is what
+    // you want.
+    #[inline]
+    pub fn combine_commutative(self, other: Fingerprint) -> Fingerprint {
+        let a = (self.1 as u128) << 64 | self.0 as u128;
+        let b = (other.1 as u128) << 64 | other.0 as u128;
+
+        let c = a.wrapping_add(b);
+
+        Fingerprint((c >> 64) as u64, c as u64)
+    }
+
     pub fn to_hex(&self) -> String {
         format!("{:x}{:x}", self.0, self.1)
     }

src/librustc/ich/impls_hir.rs

@@ -14,7 +14,7 @@
 use hir;
 use hir::map::DefPathHash;
 use hir::def_id::{DefId, LocalDefId, CrateNum, CRATE_DEF_INDEX};
-use ich::{StableHashingContext, NodeIdHashingMode};
+use ich::{StableHashingContext, NodeIdHashingMode, Fingerprint};
 use rustc_data_structures::stable_hasher::{HashStable, ToStableHashKey,
                                            StableHasher, StableHasherResult};
 use std::mem;
@@ -755,13 +755,34 @@ impl_stable_hash_for!(enum hir::ImplPolarity {
     Negative
 });
 
-impl_stable_hash_for!(struct hir::Mod {
-    inner,
-    // We are not hashing the IDs of the items contained in the module.
-    // This is harmless and matches the current behavior but it's not
-    // actually correct. See issue #40876.
-    item_ids -> _,
-});
+impl<'a> HashStable<StableHashingContext<'a>> for hir::Mod {
+    fn hash_stable<W: StableHasherResult>(&self,
+                                          hcx: &mut StableHashingContext<'a>,
+                                          hasher: &mut StableHasher<W>) {
+        let hir::Mod {
+            inner: ref inner_span,
+            ref item_ids,
+        } = *self;
+
+        inner_span.hash_stable(hcx, hasher);
+
+        // Combining the DefPathHashes directly is faster than feeding them
+        // into the hasher. Because we use a commutative combine, we also don't
+        // have to sort the array.
+        let item_ids_hash = item_ids
+            .iter()
+            .map(|id| {
+                let (def_path_hash, local_id) = id.id.to_stable_hash_key(hcx);
+                debug_assert_eq!(local_id, hir::ItemLocalId(0));
+                def_path_hash.0
+            }).fold(Fingerprint::ZERO, |a, b| {
+                a.combine_commutative(b)
+            });
+
+        item_ids.len().hash_stable(hcx, hasher);
+        item_ids_hash.hash_stable(hcx, hasher);
+    }
+}
 
 impl_stable_hash_for!(struct hir::ForeignMod {
     abi,

src/librustc_codegen_llvm/mono_item.rs

@@ -25,11 +25,10 @@ use monomorphize::Instance;
 use type_of::LayoutLlvmExt;
 use rustc::hir;
 use rustc::hir::def::Def;
-use rustc::hir::def_id::DefId;
+use rustc::hir::def_id::{DefId, LOCAL_CRATE};
 use rustc::mir::mono::{Linkage, Visibility};
 use rustc::ty::TypeFoldable;
 use rustc::ty::layout::LayoutOf;
-use syntax::attr;
 use std::fmt;
 
 pub use rustc::mir::mono::MonoItem;
@@ -173,7 +172,7 @@ fn predefine_fn<'a, 'tcx>(cx: &CodegenCx<'a, 'tcx>,
     // visibility as we're going to link this object all over the place but
     // don't want the symbols to get exported.
     if linkage != Linkage::Internal && linkage != Linkage::Private &&
-       attr::contains_name(cx.tcx.hir.krate_attrs(), "compiler_builtins") {
+       cx.tcx.is_compiler_builtins(LOCAL_CRATE) {
         unsafe {
             llvm::LLVMRustSetVisibility(lldecl, llvm::Visibility::Hidden);
         }