Auto merge of #122362 - Zoxc:rustc_driver_static_std, r=<try>

Link `std` statically in `rustc_driver`

This makes `rustc_driver` statically link to `std`. This is done by not passing `-C prefer-dynamic` when building `rustc_driver`. However building `rustc-main` won't work currently as it tries to dynamically link to both `rustc_driver` and `std` resulting in a crate graph with `std` duplicated. To fix that new command line option `-Z prefer_deps_of_dynamic` is added which prevents linking to a dylib if there's a static variant of it already statically linked into another dylib dependency.

The main motivation for this change is to enable `#[global_allocator]` to be used in `rustc_driver` allowing overriding the allocator used in rustc on all platforms.

compiler/rustc_interface/src/tests.rs

@@ -806,6 +806,7 @@ fn test_unstable_options_tracking_hash() {
     tracked!(plt, Some(true));
     tracked!(polonius, Polonius::Legacy);
     tracked!(precise_enum_drop_elaboration, false);
+    tracked!(prefer_deps_of_dynamic, true);
     tracked!(print_fuel, Some("abc".to_string()));
     tracked!(profile, true);
     tracked!(profile_emit, Some(PathBuf::from("abc")));

compiler/rustc_metadata/src/dependency_format.rs

@@ -57,7 +57,7 @@ use crate::errors::{
     RequiredPanicStrategy, RlibRequired, RustcLibRequired, TwoPanicRuntimes,
 };
 
-use rustc_data_structures::fx::FxHashMap;
+use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_hir::def_id::CrateNum;
 use rustc_middle::middle::dependency_format::{Dependencies, DependencyList, Linkage};
 use rustc_middle::ty::TyCtxt;
@@ -156,25 +156,46 @@ fn calculate_type(tcx: TyCtxt<'_>, ty: CrateType) -> DependencyList {
         Linkage::Dynamic | Linkage::IncludedFromDylib => {}
     }
 
+    let all_dylibs = || {
+        tcx.crates(()).iter().filter(|&&cnum| {
+            !tcx.dep_kind(cnum).macros_only() && tcx.used_crate_source(cnum).dylib.is_some()
+        })
+    };
+
+    let mut upstream_in_dylibs = FxHashSet::default();
+
+    if sess.opts.unstable_opts.prefer_deps_of_dynamic || tcx.features().rustc_private {
+        // Find all libraries statically linked to upstream dylibs.
+        for &cnum in all_dylibs() {
+            let deps = tcx.dylib_dependency_formats(cnum);
+            for &(depnum, style) in deps.iter() {
+                if let RequireStatic = style {
+                    upstream_in_dylibs.insert(depnum);
+                }
+            }
+        }
+    }
+
     let mut formats = FxHashMap::default();
 
     // Sweep all crates for found dylibs. Add all dylibs, as well as their
     // dependencies, ensuring there are no conflicts. The only valid case for a
     // dependency to be relied upon twice is for both cases to rely on a dylib.
-    for &cnum in tcx.crates(()).iter() {
-        if tcx.dep_kind(cnum).macros_only() {
+    for &cnum in all_dylibs() {
+        if upstream_in_dylibs.contains(&cnum) {
+            info!("skipping dylib: {}", tcx.crate_name(cnum));
+            // If this dylib is also available statically linked to another dylib
+            // we try to use that instead.
             continue;
         }
+
         let name = tcx.crate_name(cnum);
-        let src = tcx.used_crate_source(cnum);
-        if src.dylib.is_some() {
-            info!("adding dylib: {}", name);
-            add_library(tcx, cnum, RequireDynamic, &mut formats);
-            let deps = tcx.dylib_dependency_formats(cnum);
-            for &(depnum, style) in deps.iter() {
-                info!("adding {:?}: {}", style, tcx.crate_name(depnum));
-                add_library(tcx, depnum, style, &mut formats);
-            }
+        info!("adding dylib: {}", name);
+        add_library(tcx, cnum, RequireDynamic, &mut formats);
+        let deps = tcx.dylib_dependency_formats(cnum);
+        for &(depnum, style) in deps.iter() {
+            info!("adding {:?}: {}", style, tcx.crate_name(depnum));
+            add_library(tcx, depnum, style, &mut formats);
         }
     }
 

compiler/rustc_session/src/options.rs

@@ -1810,6 +1810,8 @@ options! {
         "use a more precise version of drop elaboration for matches on enums (default: yes). \
         This results in better codegen, but has caused miscompilations on some tier 2 platforms. \
         See #77382 and #74551."),
+    prefer_deps_of_dynamic: bool = (false, parse_bool, [TRACKED],
+        "prefer linking to static dependencies of dynamic libraries over available dynamic libraries (default: no)"),
     #[rustc_lint_opt_deny_field_access("use `Session::print_codegen_stats` instead of this field")]
     print_codegen_stats: bool = (false, parse_bool, [UNTRACKED],
         "print codegen statistics (default: no)"),

src/bootstrap/src/bin/rustc.rs

@@ -91,6 +91,19 @@ fn main() {
         rustc_real
     };
 
+    // Get the name of the crate we're compiling, if any.
+    let crate_name = arg("--crate-name");
+
+    // We want everything statically linked into `rustc_driver`, so remove `-C prefer-dynamic`
+    if crate_name == Some("rustc_driver") && stage != "0" {
+        if let Some(i) = args.iter().enumerate().position(|(i, a)| {
+            a == "-C" && args.get(i + 1).map(|a| a == "prefer-dynamic").unwrap_or(false)
+        }) {
+            args.remove(i);
+            args.remove(i);
+        }
+    }
+
     let mut cmd = if let Some(wrapper) = env::var_os("RUSTC_WRAPPER_REAL") {
         let mut cmd = Command::new(wrapper);
         cmd.arg(rustc_driver);
@@ -100,9 +113,6 @@ fn main() {
     };
     cmd.args(&args).env(dylib_path_var(), env::join_paths(&dylib_path).unwrap());
 
-    // Get the name of the crate we're compiling, if any.
-    let crate_name = arg("--crate-name");
-
     if let Some(crate_name) = crate_name {
         if let Some(target) = env::var_os("RUSTC_TIME") {
             if target == "all"

src/bootstrap/src/core/build_steps/compile.rs

@@ -1788,7 +1788,12 @@ impl Step for Assemble {
         let src_libdir = builder.sysroot_libdir(build_compiler, host);
         for f in builder.read_dir(&src_libdir) {
             let filename = f.file_name().into_string().unwrap();
-            if (is_dylib(&filename) || is_debug_info(&filename)) && !proc_macros.contains(&filename)
+            let can_be_rustc_dep = filename.starts_with("rustc_driver-")
+                || filename.starts_with("librustc_driver-")
+                || build_compiler.stage == 0;
+            if can_be_rustc_dep
+                && (is_dylib(&filename) || is_debug_info(&filename))
+                && !proc_macros.contains(&filename)
             {
                 builder.copy(&f.path(), &rustc_libdir.join(&filename));
             }

src/bootstrap/src/core/builder.rs

@@ -2029,10 +2029,16 @@ impl<'a> Builder<'a> {
         // When we build Rust dylibs they're all intended for intermediate
         // usage, so make sure we pass the -Cprefer-dynamic flag instead of
         // linking all deps statically into the dylib.
-        if matches!(mode, Mode::Std | Mode::Rustc) {
+        if matches!(mode, Mode::Std) {
             rustflags.arg("-Cprefer-dynamic");
         }
 
+        // We need this to prevent users of `rustc_driver` from linking to dynamically to `std`
+        // which does not work as `std` is statically linked into `rustc_driver`.
+        if stage > 0 {
+            rustflags.arg("-Zprefer-deps-of-dynamic");
+        }
+
         // When building incrementally we default to a lower ThinLTO import limit
         // (unless explicitly specified otherwise). This will produce a somewhat
         // slower code but give way better compile times.