diff --git a/src/bootstrap/doc.rs b/src/bootstrap/doc.rs
index 5f16716a0fdaf..077a86af50b2e 100644
--- a/src/bootstrap/doc.rs
+++ b/src/bootstrap/doc.rs
@@ -7,7 +7,6 @@
 //! Everything here is basically just a shim around calling either `rustbook` or
 //! `rustdoc`.
 
-use std::collections::HashSet;
 use std::fs;
 use std::io;
 use std::path::{Path, PathBuf};
@@ -554,13 +553,9 @@ impl Step for Rustc {
         let paths = builder
             .paths
             .iter()
-            .map(components_simplified)
-            .filter_map(|path| {
-                if path.get(0) == Some(&"compiler") {
-                    path.get(1).map(|p| p.to_owned())
-                } else {
-                    None
-                }
+            .filter(|path| {
+                let components = components_simplified(path);
+                components.len() >= 2 && components[0] == "compiler"
             })
             .collect::<Vec<_>>();
 
@@ -608,38 +603,22 @@ impl Step for Rustc {
         cargo.rustdocflag("--extern-html-root-url");
         cargo.rustdocflag("ena=https://docs.rs/ena/latest/");
 
-        let mut compiler_crates = HashSet::new();
-
-        if paths.is_empty() {
-            // Find dependencies for top level crates.
-            for root_crate in &["rustc_driver", "rustc_codegen_llvm", "rustc_codegen_ssa"] {
-                compiler_crates.extend(
-                    builder
-                        .in_tree_crates(root_crate, Some(target))
-                        .into_iter()
-                        .map(|krate| krate.name),
-                );
-            }
+        let root_crates = if paths.is_empty() {
+            vec![
+                INTERNER.intern_str("rustc_driver"),
+                INTERNER.intern_str("rustc_codegen_llvm"),
+                INTERNER.intern_str("rustc_codegen_ssa"),
+            ]
         } else {
-            for root_crate in paths {
-                if !builder.src.join("compiler").join(&root_crate).exists() {
-                    builder.info(&format!(
-                        "\tskipping - compiler/{} (unknown compiler crate)",
-                        root_crate
-                    ));
-                } else {
-                    compiler_crates.extend(
-                        builder
-                            .in_tree_crates(root_crate, Some(target))
-                            .into_iter()
-                            .map(|krate| krate.name),
-                    );
-                }
-            }
-        }
+            paths.into_iter().map(|p| builder.crate_paths[p]).collect()
+        };
+        // Find dependencies for top level crates.
+        let compiler_crates = root_crates.iter().flat_map(|krate| {
+            builder.in_tree_crates(krate, Some(target)).into_iter().map(|krate| krate.name)
+        });
 
         let mut to_open = None;
-        for krate in &compiler_crates {
+        for krate in compiler_crates {
             // Create all crate output directories first to make sure rustdoc uses
             // relative links.
             // FIXME: Cargo should probably do this itself.
diff --git a/src/bootstrap/lib.rs b/src/bootstrap/lib.rs
index 570a61742bcf3..b93fc791820f4 100644
--- a/src/bootstrap/lib.rs
+++ b/src/bootstrap/lib.rs
@@ -302,7 +302,9 @@ pub struct Build {
     ar: HashMap<TargetSelection, PathBuf>,
     ranlib: HashMap<TargetSelection, PathBuf>,
     // Miscellaneous
+    // allow bidirectional lookups: both name -> path and path -> name
     crates: HashMap<Interned<String>, Crate>,
+    crate_paths: HashMap<PathBuf, Interned<String>>,
     is_sudo: bool,
     ci_env: CiEnv,
     delayed_failures: RefCell<Vec<String>>,
@@ -492,6 +494,7 @@ impl Build {
             ar: HashMap::new(),
             ranlib: HashMap::new(),
             crates: HashMap::new(),
+            crate_paths: HashMap::new(),
             is_sudo,
             ci_env: CiEnv::current(),
             delayed_failures: RefCell::new(Vec::new()),
diff --git a/src/bootstrap/metadata.rs b/src/bootstrap/metadata.rs
index 59dc50be47f06..e193e70a0c417 100644
--- a/src/bootstrap/metadata.rs
+++ b/src/bootstrap/metadata.rs
@@ -49,7 +49,11 @@ pub fn build(build: &mut Build) {
                 .filter(|dep| dep.source.is_none())
                 .map(|dep| INTERNER.intern_string(dep.name))
                 .collect();
-            build.crates.insert(name, Crate { name, deps, path });
+            let krate = Crate { name, deps, path };
+            let relative_path = krate.local_path(build);
+            build.crates.insert(name, krate);
+            let existing_path = build.crate_paths.insert(relative_path, name);
+            assert!(existing_path.is_none(), "multiple crates with the same path");
         }
     }
 }
diff --git a/src/bootstrap/test.rs b/src/bootstrap/test.rs
index 81200ba60b026..9d7ea09fc8259 100644
--- a/src/bootstrap/test.rs
+++ b/src/bootstrap/test.rs
@@ -21,7 +21,6 @@ use crate::native;
 use crate::tool::{self, SourceType, Tool};
 use crate::toolstate::ToolState;
 use crate::util::{self, add_link_lib_path, dylib_path, dylib_path_var, output, t};
-use crate::Crate as CargoCrate;
 use crate::{envify, CLang, DocTests, GitRepo, Mode};
 
 const ADB_TEST_DIR: &str = "/data/tmp/work";
@@ -1901,19 +1900,10 @@ impl Step for CrateLibrustc {
     fn make_run(run: RunConfig<'_>) {
         let builder = run.builder;
         let compiler = builder.compiler(builder.top_stage, run.build_triple());
+        let krate = builder.crate_paths[&run.path];
+        let test_kind = builder.kind.into();
 
-        for krate in builder.in_tree_crates("rustc-main", Some(run.target)) {
-            if krate.path.ends_with(&run.path) {
-                let test_kind = builder.kind.into();
-
-                builder.ensure(CrateLibrustc {
-                    compiler,
-                    target: run.target,
-                    test_kind,
-                    krate: krate.name,
-                });
-            }
-        }
+        builder.ensure(CrateLibrustc { compiler, target: run.target, test_kind, krate });
     }
 
     fn run(self, builder: &Builder<'_>) {
@@ -1947,24 +1937,10 @@ impl Step for Crate {
     fn make_run(run: RunConfig<'_>) {
         let builder = run.builder;
         let compiler = builder.compiler(builder.top_stage, run.build_triple());
+        let test_kind = builder.kind.into();
+        let krate = builder.crate_paths[&run.path];
 
-        let make = |mode: Mode, krate: &CargoCrate| {
-            let test_kind = builder.kind.into();
-
-            builder.ensure(Crate {
-                compiler,
-                target: run.target,
-                mode,
-                test_kind,
-                krate: krate.name,
-            });
-        };
-
-        for krate in builder.in_tree_crates("test", Some(run.target)) {
-            if krate.path.ends_with(&run.path) {
-                make(Mode::Std, krate);
-            }
-        }
+        builder.ensure(Crate { compiler, target: run.target, mode: Mode::Std, test_kind, krate });
     }
 
     /// Runs all unit tests plus documentation tests for a given crate defined