Auto merge of #64850 - Mark-Simulacrum:dedup-dep-node, r=<try>

Remove duplicate DepNode::new

Locally this shaves off about 3 seconds of compile time for librustc, which while not much, is something for a simple PR like this.

Code is merely duplicated up from the main `DepNode::new` body.

Across 3 runs for each branch I obtained these times for compiling librustc:
master: 286.244, 285.208, 303.577
this branch: 282.175, 281.891, 282.968

r? @michaelwoerister

src/librustc/dep_graph/dep_node.rs

@@ -198,6 +198,46 @@ macro_rules! define_dep_nodes {
         }
 
         impl DepNode {
+            pub fn new_compile_codegen_unit(tcx: TyCtxt<'tcx>, s: InternedString) -> DepNode {
+                let hash = DepNodeParams::to_fingerprint(&s, tcx);
+                let dep_node = DepNode {
+                    kind: DepKind::CompileCodegenUnit,
+                    hash
+                };
+
+                if cfg!(debug_assertions) &&
+                    !dep_node.kind.can_reconstruct_query_key() &&
+                    (tcx.sess.opts.debugging_opts.incremental_info ||
+                     tcx.sess.opts.debugging_opts.query_dep_graph)
+                {
+                    tcx.dep_graph.register_dep_node_debug_str(dep_node, || {
+                        s.to_debug_str(tcx)
+                    });
+                }
+
+                dep_node
+            }
+
+            pub fn new_crate_metadata(tcx: TyCtxt<'tcx>, cnum: CrateNum) -> DepNode {
+                let hash = DepNodeParams::to_fingerprint(&cnum, tcx);
+                let dep_node = DepNode {
+                    kind: DepKind::CrateMetadata,
+                    hash
+                };
+
+                if cfg!(debug_assertions) &&
+                    !dep_node.kind.can_reconstruct_query_key() &&
+                    (tcx.sess.opts.debugging_opts.incremental_info ||
+                     tcx.sess.opts.debugging_opts.query_dep_graph)
+                {
+                    tcx.dep_graph.register_dep_node_debug_str(dep_node, || {
+                        cnum.to_debug_str(tcx)
+                    });
+                }
+
+                dep_node
+            }
+
             #[allow(unreachable_code, non_snake_case)]
             #[inline(always)]
             pub fn new<'tcx>(tcx: TyCtxt<'tcx>,

src/librustc/mir/mono.rs

@@ -6,7 +6,7 @@ use syntax::source_map::Span;
 use crate::ty::{Instance, InstanceDef, TyCtxt, SymbolName, subst::InternalSubsts};
 use crate::util::nodemap::FxHashMap;
 use crate::ty::print::obsolete::DefPathBasedNames;
-use crate::dep_graph::{WorkProductId, DepNode, WorkProduct, DepConstructor};
+use crate::dep_graph::{WorkProductId, DepNode, WorkProduct};
 use rustc_data_structures::base_n;
 use rustc_data_structures::stable_hasher::{HashStable, StableHasherResult,
                                            StableHasher};
@@ -414,7 +414,8 @@ impl<'tcx> CodegenUnit<'tcx> {
     }
 
     pub fn codegen_dep_node(&self, tcx: TyCtxt<'tcx>) -> DepNode {
-        DepNode::new(tcx, DepConstructor::CompileCodegenUnit(self.name().clone()))
+        // N.B. don't use DepNode::new here as we then inline an enormous function
+        DepNode::new_compile_codegen_unit(tcx, self.name().clone())
     }
 }
 

src/librustc/ty/context.rs

@@ -2,7 +2,7 @@
 
 use crate::arena::Arena;
 use crate::dep_graph::DepGraph;
-use crate::dep_graph::{self, DepNode, DepConstructor};
+use crate::dep_graph::{self, DepNode};
 use crate::session::Session;
 use crate::session::config::{BorrowckMode, OutputFilenames};
 use crate::session::config::CrateType;
@@ -1416,7 +1416,8 @@ impl<'tcx> TyCtxt<'tcx> {
         // We cannot use the query versions of crates() and crate_hash(), since
         // those would need the DepNodes that we are allocating here.
         for cnum in self.cstore.crates_untracked() {
-            let dep_node = DepNode::new(self, DepConstructor::CrateMetadata(cnum));
+            // N.B. don't use DepNode::new here as we then inline an enormous function
+            let dep_node = DepNode::new_crate_metadata(self, cnum);
             let crate_hash = self.cstore.crate_hash_untracked(cnum);
             self.dep_graph.with_task(dep_node,
                                      self,