diff --git a/src/librustc_codegen_llvm/allocator.rs b/src/librustc_codegen_llvm/allocator.rs
index 0beb8a8844c..7c237407c8f 100644
--- a/src/librustc_codegen_llvm/allocator.rs
+++ b/src/librustc_codegen_llvm/allocator.rs
@@ -33,7 +33,7 @@ pub(crate) unsafe fn codegen(tcx: TyCtxt, mods: &ModuleLlvm, kind: AllocatorKind
     let void = llvm::LLVMVoidTypeInContext(llcx);
 
     for method in ALLOCATOR_METHODS {
-        let mut args = Vec::new();
+        let mut args = Vec::with_capacity(method.inputs.len());
         for ty in method.inputs.iter() {
             match *ty {
                 AllocatorTy::Layout => {
diff --git a/src/librustc_codegen_llvm/attributes.rs b/src/librustc_codegen_llvm/attributes.rs
index 51380db5b23..89fe6911041 100644
--- a/src/librustc_codegen_llvm/attributes.rs
+++ b/src/librustc_codegen_llvm/attributes.rs
@@ -280,12 +280,14 @@ pub fn provide_extern(providers: &mut Providers) {
         // `NativeLibrary` internally contains information about
         // `#[link(wasm_import_module = "...")]` for example.
         let native_libs = tcx.native_libraries(cnum);
-        let mut def_id_to_native_lib = FxHashMap();
-        for lib in native_libs.iter() {
+
+        let def_id_to_native_lib = native_libs.iter().filter_map(|lib|
             if let Some(id) = lib.foreign_module {
-                def_id_to_native_lib.insert(id, lib);
+                Some((id, lib))
+            } else {
+                None
             }
-        }
+        ).collect::<FxHashMap<_, _>>();
 
         let mut ret = FxHashMap();
         for lib in tcx.foreign_modules(cnum).iter() {
@@ -296,10 +298,10 @@ pub fn provide_extern(providers: &mut Providers) {
                 Some(s) => s,
                 None => continue,
             };
-            for id in lib.foreign_items.iter() {
+            ret.extend(lib.foreign_items.iter().map(|id| {
                 assert_eq!(id.krate, cnum);
-                ret.insert(*id, module.to_string());
-            }
+                (*id, module.to_string())
+            }));
         }
 
         Lrc::new(ret)
diff --git a/src/librustc_codegen_llvm/base.rs b/src/librustc_codegen_llvm/base.rs
index 6acf884214a..a86865bdec4 100644
--- a/src/librustc_codegen_llvm/base.rs
+++ b/src/librustc_codegen_llvm/base.rs
@@ -1122,7 +1122,15 @@ impl CrateInfo {
             info.load_wasm_imports(tcx, LOCAL_CRATE);
         }
 
-        for &cnum in tcx.crates().iter() {
+        let crates = tcx.crates();
+
+        let n_crates = crates.len();
+        info.native_libraries.reserve(n_crates);
+        info.crate_name.reserve(n_crates);
+        info.used_crate_source.reserve(n_crates);
+        info.missing_lang_items.reserve(n_crates);
+
+        for &cnum in crates.iter() {
             info.native_libraries.insert(cnum, tcx.native_libraries(cnum));
             info.crate_name.insert(cnum, tcx.crate_name(cnum).to_string());
             info.used_crate_source.insert(cnum, tcx.used_crate_source(cnum));
@@ -1164,11 +1172,12 @@ impl CrateInfo {
     }
 
     fn load_wasm_imports(&mut self, tcx: TyCtxt, cnum: CrateNum) {
-        for (&id, module) in tcx.wasm_import_module_map(cnum).iter() {
+        self.wasm_imports.extend(tcx.wasm_import_module_map(cnum).iter().map(|(&id, module)| {
             let instance = Instance::mono(tcx, id);
             let import_name = tcx.symbol_name(instance);
-            self.wasm_imports.insert(import_name.to_string(), module.clone());
-        }
+
+            (import_name.to_string(), module.clone())
+        }));
     }
 }
 
diff --git a/src/librustc_codegen_llvm/llvm_util.rs b/src/librustc_codegen_llvm/llvm_util.rs
index 9e8ff204703..8456cf2f480 100644
--- a/src/librustc_codegen_llvm/llvm_util.rs
+++ b/src/librustc_codegen_llvm/llvm_util.rs
@@ -52,8 +52,9 @@ fn require_inited() {
 }
 
 unsafe fn configure_llvm(sess: &Session) {
-    let mut llvm_c_strs = Vec::new();
-    let mut llvm_args = Vec::new();
+    let n_args = sess.opts.cg.llvm_args.len();
+    let mut llvm_c_strs = Vec::with_capacity(n_args + 1);
+    let mut llvm_args = Vec::with_capacity(n_args + 1);
 
     {
         let mut add = |arg: &str| {