improve LLVM submodule handling logic in llvm::prebuilt_llvm_config

Signed-off-by: onur-ozkan <work@onurozkan.dev>

Author: onur-ozkan

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

@@ -88,9 +88,6 @@ impl LdFlags {
 /// This will return the llvm-config if it can get it (but it will not build it
 /// if not).
 pub fn prebuilt_llvm_config(builder: &Builder<'_>, target: TargetSelection) -> LlvmBuildStatus {
-    // If we have llvm submodule initialized already, sync it.
-    builder.update_existing_submodule("src/llvm-project");
-
     builder.config.maybe_download_ci_llvm();
 
     // If we're using a custom LLVM bail out here, but we can only use a
@@ -109,9 +106,16 @@ pub fn prebuilt_llvm_config(builder: &Builder<'_>, target: TargetSelection) -> L
         }
     }
 
-    // Initialize the llvm submodule if not initialized already.
-    // If submodules are disabled, this does nothing.
-    builder.config.update_submodule("src/llvm-project");
+    // Although we check if we are using CI LLVM above, certain commands (like `x test mir-opt --bless`)
+    // may call this function with different targets, which could bypass the condition above. Therefore,
+    // we need to check again whether we are not using CI LLVM before fetching the LLVM submodule.
+    //
+    // Note: `Build::update_existing_submodule` is not used intentionally as we want to fetch the submodule
+    // for non-ci LLVM cases.
+    if !builder.config.llvm_from_ci {
+        // If submodules are disabled, this does nothing.
+        builder.config.update_submodule("src/llvm-project");
+    }
 
     let root = "src/llvm-project/llvm";
     let out_dir = builder.llvm_out(target);