Remove llvm.skip-rebuild option

This was added to in 2019 to speed up rebuild times when LLVM was
modified. Now that download-ci-llvm exists, I don't think it makes sense
to support an unsound option like this that can lead to miscompiles; and
the code cleanup is nice too.

Author: jyn514

config.toml.example

@@ -46,12 +46,6 @@ changelog-seen = 2
 # Defaults to "if-available" when `channel = "dev"` and "false" otherwise.
 #download-ci-llvm = "if-available"
 
-# Indicates whether LLVM rebuild should be skipped when running bootstrap. If
-# this is `false` then the compiler's LLVM will be rebuilt whenever the built
-# version doesn't have the correct hash. If it is `true` then LLVM will never
-# be rebuilt. The default value is `false`.
-#skip-rebuild = false
-
 # Indicates whether the LLVM build is a Release or Debug build
 #optimize = true
 

src/bootstrap/config.rs

@@ -111,7 +111,6 @@ pub struct Config {
     pub backtrace_on_ice: bool,
 
     // llvm codegen options
-    pub llvm_skip_rebuild: bool,
     pub llvm_assertions: bool,
     pub llvm_tests: bool,
     pub llvm_plugins: bool,
@@ -664,7 +663,6 @@ define_config! {
 define_config! {
     /// TOML representation of how the LLVM build is configured.
     struct Llvm {
-        skip_rebuild: Option<bool> = "skip-rebuild",
         optimize: Option<bool> = "optimize",
         thin_lto: Option<bool> = "thin-lto",
         release_debuginfo: Option<bool> = "release-debuginfo",
@@ -1057,11 +1055,6 @@ impl Config {
             config.mandir = install.mandir.map(PathBuf::from);
         }
 
-        // We want the llvm-skip-rebuild flag to take precedence over the
-        // skip-rebuild config.toml option so we store it separately
-        // so that we can infer the right value
-        let mut llvm_skip_rebuild = flags.llvm_skip_rebuild;
-
         // Store off these values as options because if they're not provided
         // we'll infer default values for them later
         let mut llvm_assertions = None;
@@ -1166,7 +1159,6 @@ impl Config {
             llvm_assertions = llvm.assertions;
             llvm_tests = llvm.tests;
             llvm_plugins = llvm.plugins;
-            llvm_skip_rebuild = llvm_skip_rebuild.or(llvm.skip_rebuild);
             set(&mut config.llvm_optimize, llvm.optimize);
             set(&mut config.llvm_thin_lto, llvm.thin_lto);
             set(&mut config.llvm_release_debuginfo, llvm.release_debuginfo);
@@ -1329,7 +1321,6 @@ impl Config {
         // Now that we've reached the end of our configuration, infer the
         // default values for all options that we haven't otherwise stored yet.
 
-        config.llvm_skip_rebuild = llvm_skip_rebuild.unwrap_or(false);
         config.llvm_assertions = llvm_assertions.unwrap_or(false);
         config.llvm_tests = llvm_tests.unwrap_or(false);
         config.llvm_plugins = llvm_plugins.unwrap_or(false);

src/bootstrap/flags.rs

@@ -67,8 +67,6 @@ pub struct Flags {
     // true => deny, false => warn
     pub deny_warnings: Option<bool>,
 
-    pub llvm_skip_rebuild: Option<bool>,
-
     pub rust_profile_use: Option<String>,
     pub rust_profile_generate: Option<String>,
 
@@ -249,14 +247,6 @@ To learn more about a subcommand, run `./x.py <subcommand> -h`",
         opts.optopt("", "error-format", "rustc error format", "FORMAT");
         opts.optflag("", "json-output", "use message-format=json");
         opts.optopt("", "color", "whether to use color in cargo and rustc output", "STYLE");
-        opts.optopt(
-            "",
-            "llvm-skip-rebuild",
-            "whether rebuilding llvm should be skipped \
-             a VALUE of TRUE indicates that llvm will not be rebuilt \
-             VALUE overrides the skip-rebuild option in config.toml.",
-            "VALUE",
-        );
         opts.optopt(
             "",
             "rust-profile-generate",
@@ -707,9 +697,6 @@ Arguments:
                 .collect::<Vec<_>>(),
             include_default_paths: matches.opt_present("include-default-paths"),
             deny_warnings: parse_deny_warnings(&matches),
-            llvm_skip_rebuild: matches.opt_str("llvm-skip-rebuild").map(|s| s.to_lowercase()).map(
-                |s| s.parse::<bool>().expect("`llvm-skip-rebuild` should be either true or false"),
-            ),
             color: matches
                 .opt_get_default("color", Color::Auto)
                 .expect("`color` should be `always`, `never`, or `auto`"),

src/bootstrap/native.rs

@@ -109,15 +109,6 @@ pub fn prebuilt_llvm_config(
     let stamp = out_dir.join("llvm-finished-building");
     let stamp = HashStamp::new(stamp, builder.in_tree_llvm_info.sha());
 
-    if builder.config.llvm_skip_rebuild && stamp.path.exists() {
-        builder.info(
-            "Warning: \
-                Using a potentially stale build of LLVM; \
-                This may not behave well.",
-        );
-        return Ok(res);
-    }
-
     if stamp.is_done() {
         if stamp.hash.is_none() {
             builder.info(

src/doc/rustc/src/platform-support/armeb-unknown-linux-gnueabi.md

@@ -26,7 +26,6 @@ Therefore, you can build Rust with support for the target by adding it to the ta
 ```toml
 [llvm]
 download-ci-llvm = false
-skip-rebuild = true
 optimize = true
 ninja = true
 targets = "ARM;X86"