diff --git a/compiler/rustc_codegen_llvm/src/back/lto.rs b/compiler/rustc_codegen_llvm/src/back/lto.rs
index cf5badf7b99c1..f28af4ba49bad 100644
--- a/compiler/rustc_codegen_llvm/src/back/lto.rs
+++ b/compiler/rustc_codegen_llvm/src/back/lto.rs
@@ -616,7 +616,9 @@ pub(crate) fn run_pass_manager(
         }
         let opt_stage = if thin { llvm::OptStage::ThinLTO } else { llvm::OptStage::FatLTO };
         let opt_level = config.opt_level.unwrap_or(config::OptLevel::No);
-        write::llvm_optimize(cgcx, dcx, module, config, opt_level, opt_stage)?;
+        // We will run this again with different values in the context of automatic differentiation.
+        let first_run = true;
+        write::llvm_optimize(cgcx, dcx, module, config, opt_level, opt_stage, first_run)?;
     }
     debug!("lto done");
     Ok(())
diff --git a/compiler/rustc_codegen_llvm/src/back/write.rs b/compiler/rustc_codegen_llvm/src/back/write.rs
index 2bbe1f03f91d8..e09aec69ec44c 100644
--- a/compiler/rustc_codegen_llvm/src/back/write.rs
+++ b/compiler/rustc_codegen_llvm/src/back/write.rs
@@ -549,6 +549,7 @@ pub(crate) unsafe fn llvm_optimize(
     config: &ModuleConfig,
     opt_level: config::OptLevel,
     opt_stage: llvm::OptStage,
+    first_run: bool,
 ) -> Result<(), FatalError> {
     // Enzyme:
     // We want to simplify / optimize functions before AD.
@@ -556,16 +557,23 @@ pub(crate) unsafe fn llvm_optimize(
     // tend to reduce AD performance. Therefore activate them first, then differentiate the code
     // and finally re-optimize the module, now with all optimizations available.
     // RIP compile time.
-    // let unroll_loops =
-    //     opt_level != config::OptLevel::Size && opt_level != config::OptLevel::SizeMin;
 
+    let unroll_loops;
+    let vectorize_slp;
+    let vectorize_loop;
 
-
-    let _unroll_loops =
+    if first_run {
+        unroll_loops = false;
+        vectorize_slp = false;
+        vectorize_loop = false;
+    } else {
+        unroll_loops =
         opt_level != config::OptLevel::Size && opt_level != config::OptLevel::SizeMin;
-    let unroll_loops = false;
-    let vectorize_slp = false;
-    let vectorize_loop = false;
+        vectorize_slp = config.vectorize_slp;
+        vectorize_loop = config.vectorize_loop;
+        dbg!("Enzyme: Running with unroll_loops: {}, vectorize_slp: {}, vectorize_loop: {}", unroll_loops, vectorize_slp, vectorize_loop);
+    }
+
     let using_thin_buffers = opt_stage == llvm::OptStage::PreLinkThinLTO || config.bitcode_needed();
     let pgo_gen_path = get_pgo_gen_path(config);
     let pgo_use_path = get_pgo_use_path(config);
@@ -987,11 +995,13 @@ pub(crate) unsafe fn enzyme_ad(
         item.inputs.into_iter().map(|x| to_enzyme_typetree(x, llvm_data_layout, llcx)).collect();
     let output_tt = to_enzyme_typetree(item.output, llvm_data_layout, llcx);
 
-    let mut opt = 1;
-    if std::env::var("ENZYME_DISABLE_OPTS").is_ok() {
-        opt = 0;
+    let mut fnc_opt = false;
+    if std::env::var("ENZYME_ENABLE_FNC_OPT").is_ok() {
+        dbg!("Disabling optimizations for Enzyme");
+        fnc_opt = true;
     }
-    let logic_ref: EnzymeLogicRef = CreateEnzymeLogic(opt as u8);
+
+    let logic_ref: EnzymeLogicRef = CreateEnzymeLogic(fnc_opt as u8);
     let type_analysis: EnzymeTypeAnalysisRef =
         CreateTypeAnalysis(logic_ref, std::ptr::null_mut(), std::ptr::null_mut(), 0);
 
@@ -1051,7 +1061,7 @@ pub(crate) unsafe fn differentiate(
     cgcx: &CodegenContext<LlvmCodegenBackend>,
     diff_items: Vec<AutoDiffItem>,
     _typetrees: FxHashMap<String, DiffTypeTree>,
-    _config: &ModuleConfig,
+    config: &ModuleConfig,
 ) -> Result<(), FatalError> {
     for item in &diff_items {
         trace!("{}", item);
@@ -1086,6 +1096,7 @@ pub(crate) unsafe fn differentiate(
         llvm::set_max_type_offset(width);
     }
 
+    let differentiate = !diff_items.is_empty();
     for item in diff_items {
         let res = enzyme_ad(llmod, llcx, &diag_handler, item);
         assert!(res.is_ok());
@@ -1126,6 +1137,23 @@ pub(crate) unsafe fn differentiate(
         }
     }
 
+
+    if std::env::var("ENZYME_NO_MOD_OPT_AFTER").is_ok() || !differentiate {
+        trace!("Skipping module optimization after automatic differentiation");
+    } else {
+        if let Some(opt_level) = config.opt_level {
+            let opt_stage = match cgcx.lto {
+                Lto::Fat => llvm::OptStage::PreLinkFatLTO,
+                Lto::Thin | Lto::ThinLocal => llvm::OptStage::PreLinkThinLTO,
+                _ if cgcx.opts.cg.linker_plugin_lto.enabled() => llvm::OptStage::PreLinkThinLTO,
+                _ => llvm::OptStage::PreLinkNoLTO,
+            };
+            let first_run = false;
+            dbg!("Running Module Optimization after differentiation");
+            llvm_optimize(cgcx, &diag_handler, module, config, opt_level, opt_stage, first_run)?;
+        }
+    }
+
     Ok(())
 }
 
@@ -1198,7 +1226,9 @@ pub(crate) unsafe fn optimize(
             _ if cgcx.opts.cg.linker_plugin_lto.enabled() => llvm::OptStage::PreLinkThinLTO,
             _ => llvm::OptStage::PreLinkNoLTO,
         };
-        return llvm_optimize(cgcx, dcx, module, config, opt_level, opt_stage);
+        // Second run only relevant for AD
+        let first_run = true;
+        return llvm_optimize(cgcx, dcx, module, config, opt_level, opt_stage, first_run);
     }
     Ok(())
 }