Fix issue #110087

Three tasks have been implemented here.

Add a new `download-ci-llvm = if-unchange` option and enable if by
default for `profile = codegen`.

Include all build artifacts by traversing the llvm-project build output,
Keep the downloadable llvm the same state as if you have just run a full
source build.

After selecting the codegen profile during ./x.py setup, the submodule
will be automatically downloaded.

config.example.toml

@@ -30,7 +30,7 @@
 #
 # If `change-id` does not match the version that is currently running,
 # `x.py` will prompt you to update it and check the related PR for more details.
-change-id = 117435
+change-id = 116881
 
 # =============================================================================
 # Tweaking how LLVM is compiled
@@ -42,11 +42,15 @@ change-id = 117435
 # Unless you're developing for a target where Rust CI doesn't build a compiler
 # toolchain or changing LLVM locally, you probably want to leave this enabled.
 #
-# All tier 1 targets are currently supported; set this to `"if-available"` if
-# you are not sure whether you're on a tier 1 target.
+# Set this to `"if-available"` if you are not sure whether you're on a tier 1 
+# target. All tier 1 targets are currently supported;
 #
 # We also currently only support this when building LLVM for the build triple.
 #
+# Set this to `"if-unchanged"` to only download if the llvm-project have not 
+# been modified. (If there are no changes or if built from tarball source, 
+# the logic is the same as "if-available")
+#
 # Note that many of the LLVM options are not currently supported for
 # downloading. Currently only the "assertions" option can be toggled.
 #download-ci-llvm = if rust.channel == "dev" { "if-available" } else { false }

src/bootstrap/defaults/config.codegen.toml

@@ -10,7 +10,7 @@ assertions = true
 # enable warnings during the llvm compilation
 enable-warnings = true
 # build llvm from source
-download-ci-llvm = false
+download-ci-llvm = "if-unchanged"
 
 [rust]
 # This enables `RUSTC_LOG=debug`, avoiding confusing situations

src/bootstrap/download-ci-llvm-stamp

@@ -1,4 +1,4 @@
 Change this file to make users of the `download-ci-llvm` configuration download
 a new version of LLVM from CI, even if the LLVM submodule hasn’t changed.
 
-Last change is for: https://github.com/rust-lang/rust/pull/113996
+Last change is for: https://github.com/rust-lang/rust/pull/116881

src/bootstrap/src/core/build_steps/dist.rs

@@ -2219,23 +2219,19 @@ impl Step for RustDev {
         builder.ensure(crate::core::build_steps::llvm::Lld { target });
 
         let src_bindir = builder.llvm_out(target).join("bin");
-        // If updating this list, you likely want to change
+        // If updating this, you likely want to change
         // src/bootstrap/download-ci-llvm-stamp as well, otherwise local users
         // will not pick up the extra file until LLVM gets bumped.
-        for bin in &[
-            "llvm-config",
-            "llvm-ar",
-            "llvm-objdump",
-            "llvm-profdata",
-            "llvm-bcanalyzer",
-            "llvm-cov",
-            "llvm-dwp",
-            "llvm-nm",
-            "llvm-dwarfdump",
-            "llvm-dis",
-            "llvm-tblgen",
-        ] {
-            tarball.add_file(src_bindir.join(exe(bin, target)), "bin", 0o755);
+        // We should include all the build artifacts obtained from a source build,
+        // so that you can use the downloadable LLVM as if you’ve just run a full source build.
+        if src_bindir.exists() {
+            for entry in walkdir::WalkDir::new(&src_bindir) {
+                let entry = t!(entry);
+                if entry.file_type().is_file() && !entry.path_is_symlink() {
+                    let name = entry.file_name().to_str().unwrap();
+                    tarball.add_file(src_bindir.join(name), "bin", 0o755);
+                }
+            }
         }
 
         // We don't build LLD on some platforms, so only add it if it exists

src/bootstrap/src/core/build_steps/setup.rs

@@ -147,6 +147,15 @@ impl Step for Profile {
     }
 
     fn run(self, builder: &Builder<'_>) {
+        // During ./x.py setup once you select the codegen profile.
+        // The submodule will be downloaded. It does not work in the
+        // tarball case since they don't include Git and submodules
+        // are already included.
+        if !builder.rust_info().is_from_tarball() {
+            if self == Profile::Codegen {
+                builder.update_submodule(&Path::new("src/llvm-project"));
+            }
+        }
         setup(&builder.build.config, self)
     }
 }

src/bootstrap/src/core/config/config.rs

@@ -19,6 +19,7 @@ use std::process::Command;
 use std::str::FromStr;
 
 use crate::core::build_steps::compile::CODEGEN_BACKEND_PREFIX;
+use crate::core::build_steps::llvm;
 use crate::core::config::flags::{Color, Flags, Warnings};
 use crate::utils::cache::{Interned, INTERNER};
 use crate::utils::channel::{self, GitInfo};
@@ -1530,17 +1531,7 @@ impl Config {
             config.llvm_build_config = llvm.build_config.clone().unwrap_or(Default::default());
 
             let asserts = llvm_assertions.unwrap_or(false);
-            config.llvm_from_ci = match llvm.download_ci_llvm {
-                Some(StringOrBool::String(s)) => {
-                    assert_eq!(s, "if-available", "unknown option `{s}` for download-ci-llvm");
-                    crate::core::build_steps::llvm::is_ci_llvm_available(&config, asserts)
-                }
-                Some(StringOrBool::Bool(b)) => b,
-                None => {
-                    config.channel == "dev"
-                        && crate::core::build_steps::llvm::is_ci_llvm_available(&config, asserts)
-                }
-            };
+            config.llvm_from_ci = config.parse_download_ci_llvm(llvm.download_ci_llvm, asserts);
 
             if config.llvm_from_ci {
                 // None of the LLVM options, except assertions, are supported
@@ -2104,6 +2095,94 @@ impl Config {
 
         Some(commit.to_string())
     }
+
+    fn parse_download_ci_llvm(
+        &self,
+        download_ci_llvm: Option<StringOrBool>,
+        asserts: bool,
+    ) -> bool {
+        match download_ci_llvm {
+            None => self.channel == "dev" && llvm::is_ci_llvm_available(&self, asserts),
+            Some(StringOrBool::Bool(b)) => b,
+            Some(StringOrBool::String(s)) if s == "if-available" => {
+                llvm::is_ci_llvm_available(&self, asserts)
+            }
+            Some(StringOrBool::String(s)) if s == "if-unchanged" => {
+                // Git is needed to track modifications here, but tarball source is not available.
+                // If not modified here or built through tarball source, we maintain consistency
+                // with '"if available"'.
+                if !self.rust_info.is_from_tarball()
+                    && self
+                        .last_modified_commit(&["src/llvm-project"], "download-ci-llvm", true)
+                        .is_none()
+                {
+                    // there are some untracked changes in the the given paths.
+                    false
+                } else {
+                    llvm::is_ci_llvm_available(&self, asserts)
+                }
+            }
+            Some(StringOrBool::String(other)) => {
+                panic!("unrecognized option for download-ci-llvm: {:?}", other)
+            }
+        }
+    }
+
+    /// Returns the last commit in which any of `modified_paths` were changed,
+    /// or `None` if there are untracked changes in the working directory and `if_unchanged` is true.
+    pub fn last_modified_commit(
+        &self,
+        modified_paths: &[&str],
+        option_name: &str,
+        if_unchanged: bool,
+    ) -> Option<String> {
+        // Handle running from a directory other than the top level
+        let top_level = output(self.git().args(&["rev-parse", "--show-toplevel"]));
+        let top_level = top_level.trim_end();
+
+        // Look for a version to compare to based on the current commit.
+        // Only commits merged by bors will have CI artifacts.
+        let merge_base = output(
+            self.git()
+                .arg("rev-list")
+                .arg(format!("--author={}", self.stage0_metadata.config.git_merge_commit_email))
+                .args(&["-n1", "--first-parent", "HEAD"]),
+        );
+        let commit = merge_base.trim_end();
+        if commit.is_empty() {
+            println!("error: could not find commit hash for downloading components from CI");
+            println!("help: maybe your repository history is too shallow?");
+            println!("help: consider disabling `{option_name}`");
+            println!("help: or fetch enough history to include one upstream commit");
+            crate::exit!(1);
+        }
+
+        // Warn if there were changes to the compiler or standard library since the ancestor commit.
+        let mut git = self.git();
+        git.args(&["diff-index", "--quiet", &commit, "--"]);
+
+        for path in modified_paths {
+            git.arg(format!("{top_level}/{path}"));
+        }
+
+        let has_changes = !t!(git.status()).success();
+        if has_changes {
+            if if_unchanged {
+                if self.verbose > 0 {
+                    println!(
+                        "warning: saw changes to one of {modified_paths:?} since {commit}; \
+                            ignoring `{option_name}`"
+                    );
+                }
+                return None;
+            }
+            println!(
+                "warning: `{option_name}` is enabled, but there are changes to one of {modified_paths:?}"
+            );
+        }
+
+        Some(commit.to_string())
+    }
 }
 
 fn set<T>(field: &mut T, val: Option<T>) {

src/bootstrap/src/lib.rs

@@ -77,7 +77,7 @@ const LLD_FILE_NAMES: &[&str] = &["ld.lld", "ld64.lld", "lld-link", "wasm-ld"];
 ///
 /// If you make any major changes (such as adding new values or changing default values), please
 /// ensure that the associated PR ID is added to the end of this list.
-pub const CONFIG_CHANGE_HISTORY: &[usize] = &[115898, 116998, 117435];
+pub const CONFIG_CHANGE_HISTORY: &[usize] = &[115898, 116998, 117435, 116881];
 
 /// Extra --check-cfg to add when building
 /// (Mode restriction, config name, config values (if any))