Rollup merge of rust-lang#79970 - bjorn3:no_unnecessary_llvm_checkout, r=Mark-Simulacrum

Misc rustbuild improvements when the LLVM backend isn't used

* Don't checkout llvm-project
* Don't require cmake and ninja

Fixes rust-lang#78564

Author: JohnTitor

src/bootstrap/bootstrap.py

@@ -897,13 +897,17 @@ def update_submodules(self):
         filtered_submodules = []
         submodules_names = []
         llvm_checked_out = os.path.exists(os.path.join(self.rust_root, "src/llvm-project/.git"))
+        external_llvm_provided = self.get_toml('llvm-config') or self.downloading_llvm()
+        llvm_needed = not self.get_toml('codegen-backends', 'rust') \
+            or "llvm" in self.get_toml('codegen-backends', 'rust')
         for module in submodules:
             if module.endswith("llvm-project"):
-                # Don't sync the llvm-project submodule either if an external LLVM
-                # was provided, or if we are downloading LLVM. Also, if the
-                # submodule has been initialized already, sync it anyways so that
-                # it doesn't mess up contributor pull requests.
-                if self.get_toml('llvm-config') or self.downloading_llvm():
+                # Don't sync the llvm-project submodule if an external LLVM was
+                # provided, if we are downloading LLVM or if the LLVM backend is
+                # not being built. Also, if the submodule has been initialized
+                # already, sync it anyways so that it doesn't mess up contributor
+                # pull requests.
+                if external_llvm_provided or not llvm_needed:
                     if self.get_toml('lld') != 'true' and not llvm_checked_out:
                         continue
             check = self.check_submodule(module, slow_submodules)

src/bootstrap/sanity.rs

@@ -17,6 +17,7 @@ use std::process::Command;
 
 use build_helper::{output, t};
 
+use crate::cache::INTERNER;
 use crate::config::Target;
 use crate::Build;
 
@@ -79,18 +80,19 @@ pub fn check(build: &mut Build) {
     }
 
     // We need cmake, but only if we're actually building LLVM or sanitizers.
-    let building_llvm = build
-        .hosts
-        .iter()
-        .map(|host| {
-            build
-                .config
-                .target_config
-                .get(host)
-                .map(|config| config.llvm_config.is_none())
-                .unwrap_or(true)
-        })
-        .any(|build_llvm_ourselves| build_llvm_ourselves);
+    let building_llvm = build.config.rust_codegen_backends.contains(&INTERNER.intern_str("llvm"))
+        && build
+            .hosts
+            .iter()
+            .map(|host| {
+                build
+                    .config
+                    .target_config
+                    .get(host)
+                    .map(|config| config.llvm_config.is_none())
+                    .unwrap_or(true)
+            })
+            .any(|build_llvm_ourselves| build_llvm_ourselves);
     if building_llvm || build.config.any_sanitizers_enabled() {
         cmd_finder.must_have("cmake");
     }
@@ -147,10 +149,12 @@ pub fn check(build: &mut Build) {
         }
     }
 
-    // Externally configured LLVM requires FileCheck to exist
-    let filecheck = build.llvm_filecheck(build.build);
-    if !filecheck.starts_with(&build.out) && !filecheck.exists() && build.config.codegen_tests {
-        panic!("FileCheck executable {:?} does not exist", filecheck);
+    if build.config.rust_codegen_backends.contains(&INTERNER.intern_str("llvm")) {
+        // Externally configured LLVM requires FileCheck to exist
+        let filecheck = build.llvm_filecheck(build.build);
+        if !filecheck.starts_with(&build.out) && !filecheck.exists() && build.config.codegen_tests {
+            panic!("FileCheck executable {:?} does not exist", filecheck);
+        }
     }
 
     for target in &build.targets {