Auto merge of #77117 - davidtwco:issue-34651-split-dwarf, r=nagisa

cg_llvm: split dwarf support

cc #34651

This PR adds initial support for Split DWARF to rustc, based on the implementation in Clang.

##### Current Status
This PR currently has functioning split-dwarf, running rustc with `-Zsplit-dwarf=split` when compiling a binary will produce a `dwp` alongside the binary, which contains the linked dwarf objects.

```shell-session
$ rustc -Cdebuginfo=2 -Zsplit-dwarf=split -C save-temps ./foo.rs
$ ls foo*
foo
foo.belfx9afw9cmv8.rcgu.dwo
foo.belfx9afw9cmv8.rcgu.o
foo.foo.7rcbfp3g-cgu.0.rcgu.dwo
foo.foo.7rcbfp3g-cgu.0.rcgu.o
foo.foo.7rcbfp3g-cgu.1.rcgu.dwo
foo.foo.7rcbfp3g-cgu.1.rcgu.o
foo.foo.7rcbfp3g-cgu.2.rcgu.dwo
foo.foo.7rcbfp3g-cgu.2.rcgu.o
foo.foo.7rcbfp3g-cgu.3.rcgu.dwo
foo.foo.7rcbfp3g-cgu.3.rcgu.o
foo.foo.7rcbfp3g-cgu.4.rcgu.dwo
foo.foo.7rcbfp3g-cgu.4.rcgu.o
foo.foo.7rcbfp3g-cgu.5.rcgu.dwo
foo.foo.7rcbfp3g-cgu.5.rcgu.o
foo.foo.7rcbfp3g-cgu.6.rcgu.dwo
foo.foo.7rcbfp3g-cgu.6.rcgu.o
foo.foo.7rcbfp3g-cgu.7.rcgu.dwo
foo.foo.7rcbfp3g-cgu.7.rcgu.o
foo.dwp
foo.rs
$ readelf -wi foo.foo.7rcbfp3g-cgu.0.rcgu.o
# ...
  Compilation Unit @ offset 0x90:
   Length:        0x2c (32-bit)
   Version:       4
   Abbrev Offset: 0x5b
   Pointer Size:  8
 <0><9b>: Abbrev Number: 1 (DW_TAG_compile_unit)
    <9c>   DW_AT_stmt_list   : 0xe8
    <a0>   DW_AT_comp_dir    : (indirect string, offset: 0x13b): /home/david/Projects/rust/rust0
    <a4>   DW_AT_GNU_dwo_name: (indirect string, offset: 0x15b): foo.foo.7rcbfp3g-cgu.0.rcgu.dwo
    <a8>   DW_AT_GNU_dwo_id  : 0x357472a2b032d7b9
    <b0>   DW_AT_low_pc      : 0x0
    <b8>   DW_AT_ranges      : 0x40
    <bc>   DW_AT_GNU_addr_base: 0x0
# ...
```

##### To-Do
I've opened this PR as a draft to get feedback and work out how we'd expect rustc to work when Split DWARF is requested. It might be easier to read the PR commit-by-commit.

- [ ] Add error when Split DWARF is requested on platforms where it doesn't make sense.
- [x] Determine whether or not there should be a single `dwo` output from rustc, or one per codegen-unit as exists currently.
- [x] Add tests.
- [x] Fix `single` mode - currently single mode doesn't change the invocation of `addPassesToEmitFile`, which is correct, but it also needs to change the split dwarf path provided to `createCompileUnit` and `createTargetMachine` so that it's just the final binary (currently it is still a non-existent `dwo` file).

r? `@nagisa`
cc `@michaelwoerister` `@eddyb` `@alexcrichton` `@rust-lang/wg-incr-comp`

3 files changed, 30 insertions, 12 deletions

diff --git a/src/bootstrap/compile.rs b/src/bootstrap/compile.rs
index cdad1cb4d49..fbebb26c746 100644
--- a/src/bootstrap/compile.rs
+++ b/src/bootstrap/compile.rs
@@ -969,15 +969,25 @@ impl Step for Assemble {
 
         copy_codegen_backends_to_sysroot(builder, build_compiler, target_compiler);
 
+        // We prepend this bin directory to the user PATH when linking Rust binaries. To
+        // avoid shadowing the system LLD we rename the LLD we provide to `rust-lld`.
         let libdir = builder.sysroot_libdir(target_compiler, target_compiler.host);
+        let libdir_bin = libdir.parent().unwrap().join("bin");
+        t!(fs::create_dir_all(&libdir_bin));
+
         if let Some(lld_install) = lld_install {
             let src_exe = exe("lld", target_compiler.host);
             let dst_exe = exe("rust-lld", target_compiler.host);
-            // we prepend this bin directory to the user PATH when linking Rust binaries. To
-            // avoid shadowing the system LLD we rename the LLD we provide to `rust-lld`.
-            let dst = libdir.parent().unwrap().join("bin");
-            t!(fs::create_dir_all(&dst));
-            builder.copy(&lld_install.join("bin").join(&src_exe), &dst.join(&dst_exe));
+            builder.copy(&lld_install.join("bin").join(&src_exe), &libdir_bin.join(&dst_exe));
+        }
+
+        // Similarly, copy `llvm-dwp` into libdir for Split DWARF.
+        {
+            let src_exe = exe("llvm-dwp", target_compiler.host);
+            let dst_exe = exe("rust-llvm-dwp", target_compiler.host);
+            let llvm_config_bin = builder.ensure(native::Llvm { target: target_compiler.host });
+            let llvm_bin_dir = llvm_config_bin.parent().unwrap();
+            builder.copy(&llvm_bin_dir.join(&src_exe), &libdir_bin.join(&dst_exe));
         }
 
         // Ensure that `libLLVM.so` ends up in the newly build compiler directory,
diff --git a/src/bootstrap/dist.rs b/src/bootstrap/dist.rs
index 360e51ed2bb..25905895116 100644
--- a/src/bootstrap/dist.rs
+++ b/src/bootstrap/dist.rs
@@ -523,17 +523,20 @@ impl Step for Rustc {
             // component for now.
             maybe_install_llvm_runtime(builder, host, image);
 
+            let src_dir = builder.sysroot_libdir(compiler, host).parent().unwrap().join("bin");
+            let dst_dir = image.join("lib/rustlib").join(&*host.triple).join("bin");
+            t!(fs::create_dir_all(&dst_dir));
+
             // Copy over lld if it's there
             if builder.config.lld_enabled {
                 let exe = exe("rust-lld", compiler.host);
-                let src =
-                    builder.sysroot_libdir(compiler, host).parent().unwrap().join("bin").join(&exe);
-                // for the rationale about this rename check `compile::copy_lld_to_sysroot`
-                let dst = image.join("lib/rustlib").join(&*host.triple).join("bin").join(&exe);
-                t!(fs::create_dir_all(&dst.parent().unwrap()));
-                builder.copy(&src, &dst);
+                builder.copy(&src_dir.join(&exe), &dst_dir.join(&exe));
             }
 
+            // Copy over llvm-dwp if it's there
+            let exe = exe("rust-llvm-dwp", compiler.host);
+            builder.copy(&src_dir.join(&exe), &dst_dir.join(&exe));
+
             // Man pages
             t!(fs::create_dir_all(image.join("share/man/man1")));
             let man_src = builder.src.join("src/doc/man");
diff --git a/src/bootstrap/test.rs b/src/bootstrap/test.rs
index 78b5de7897d..b99692e8ba5 100644
--- a/src/bootstrap/test.rs
+++ b/src/bootstrap/test.rs
@@ -897,7 +897,12 @@ default_test!(Incremental {
     suite: "incremental"
 });
 
-default_test!(Debuginfo { path: "src/test/debuginfo", mode: "debuginfo", suite: "debuginfo" });
+default_test_with_compare_mode!(Debuginfo {
+    path: "src/test/debuginfo",
+    mode: "debuginfo",
+    suite: "debuginfo",
+    compare_mode: "split-dwarf"
+});
 
 host_test!(UiFullDeps { path: "src/test/ui-fulldeps", mode: "ui", suite: "ui-fulldeps" });