add check for noinline attribute

Author: Shourya742

Diff for: compiler/rustc_codegen_llvm/src/attributes.rs

@@ -28,6 +28,10 @@ pub(crate) fn apply_to_callsite(callsite: &Value, idx: AttributePlace, attrs: &[
     }
 }
 
+pub(crate) fn has_attr(llfn: &Value, idx: AttributePlace, attr: &Attribute) -> bool {
+    llvm::HasAttributeAtIndex(llfn, idx, attr)
+}
+
 /// Get LLVM attribute for the provided inline heuristic.
 #[inline]
 fn inline_attr<'ll>(cx: &CodegenCx<'ll, '_>, inline: InlineAttr) -> Option<&'ll Attribute> {

Diff for: compiler/rustc_codegen_llvm/src/back/lto.rs

@@ -673,6 +673,14 @@ pub(crate) fn run_pass_manager(
             let name = std::str::from_utf8(name).unwrap();
 
             if name.starts_with("__enzyme") {
+                // Ensure `noinline` is present before replacing it.
+                // This is not strictly necessary for correctness, but serves as a sanity check
+                // in case the autodiff pass stops injecting `noinline` in the future.
+                assert!(
+                    attributes::has_attr(function, llvm::AttributeKind::NoInline, Function),
+                    "Expected __enzyme function to have 'noinline' before adding 'alwaysinline'"
+                );
+
                 let attr = llvm::AttributeKind::AlwaysInline.create_attr(cx.llcx);
                 attributes::apply_to_llfn(function, Function, &[attr]);
             }

Diff for: compiler/rustc_codegen_llvm/src/llvm/mod.rs

@@ -41,6 +41,14 @@ pub(crate) fn AddFunctionAttributes<'ll>(
     }
 }
 
+pub(crate) fn HasAttributeAtIndex<'ll>(
+    llfn: &'ll Value,
+    idx: AttributePlace,
+    attr: &'ll Attribute,
+) -> bool {
+    unsafe { LLVMRustHasAttributeAtIndex(llfn, idx.as_uint(), attrs.as_ptr()) }
+}
+
 pub(crate) fn AddCallSiteAttributes<'ll>(
     callsite: &'ll Value,
     idx: AttributePlace,