Rollup merge of #122632 - onur-ozkan:fix-llvm-caching-bug, r=albertlarsan68

fetch submodule before checking llvm stamp

Previously, we were checking the LLVM stamp before fetching the submodule which leads to not being able to compile llvm on submodule updates.

Fixes #122612
Fixes #122787

src/bootstrap/src/core/build_steps/llvm.rs

@@ -76,6 +76,9 @@ pub fn prebuilt_llvm_config(
     builder: &Builder<'_>,
     target: TargetSelection,
 ) -> Result<LlvmResult, Meta> {
+    // If we have llvm submodule initialized already, sync it.
+    builder.update_existing_submodule(&Path::new("src").join("llvm-project"));
+
     builder.config.maybe_download_ci_llvm();
 
     // If we're using a custom LLVM bail out here, but we can only use a
@@ -94,6 +97,9 @@ pub fn prebuilt_llvm_config(
         }
     }
 
+    // Initialize the llvm submodule if not initialized already.
+    builder.update_submodule(&Path::new("src").join("llvm-project"));
+
     let root = "src/llvm-project/llvm";
     let out_dir = builder.llvm_out(target);
 
@@ -280,7 +286,6 @@ fn run(self, builder: &Builder<'_>) -> LlvmResult {
             Err(m) => m,
         };
 
-        builder.update_submodule(&Path::new("src").join("llvm-project"));
         if builder.llvm_link_shared() && target.is_windows() {
             panic!("shared linking to LLVM is not currently supported on {}", target.triple);
         }

src/bootstrap/src/lib.rs

@@ -630,6 +630,18 @@ pub fn update_existing_submodules(&self) {
         }
     }
 
+    /// Updates the given submodule only if it's initialized already; nothing happens otherwise.
+    pub fn update_existing_submodule(&self, submodule: &Path) {
+        // Avoid running git when there isn't a git checkout.
+        if !self.config.submodules(self.rust_info()) {
+            return;
+        }
+
+        if GitInfo::new(false, submodule).is_managed_git_subrepository() {
+            self.update_submodule(submodule);
+        }
+    }
+
     /// Executes the entire build, as configured by the flags and configuration.
     pub fn build(&mut self) {
         unsafe {