#31820 - Utilize if..let instead of single match branch

src/librustc_trans/back/link.rs

@@ -226,9 +226,8 @@ fn symbol_hash<'tcx>(tcx: &ty::ctxt<'tcx>,
 }
 
 fn get_symbol_hash<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>, t: Ty<'tcx>) -> String {
-    match ccx.type_hashcodes().borrow().get(&t) {
-        Some(h) => return h.to_string(),
-        None => {}
+    if let Some(h) = ccx.type_hashcodes().borrow().get(&t) {
+        return h.to_string()
     }
 
     let mut symbol_hasher = ccx.symbol_hasher().borrow_mut();
@@ -315,9 +314,8 @@ pub fn mangle<PI: Iterator<Item=InternedString>>(path: PI, hash: Option<&str>) -
         push(&mut n, &data);
     }
 
-    match hash {
-        Some(s) => push(&mut n, s),
-        None => {}
+    if let Some(s) = hash {
+        push(&mut n, s)
     }
 
     n.push('E'); // End name-sequence.

src/librustc_trans/trans/base.rs

@@ -150,9 +150,8 @@ impl Drop for _InsnCtxt {
 pub fn push_ctxt(s: &'static str) -> _InsnCtxt {
     debug!("new InsnCtxt: {}", s);
     TASK_LOCAL_INSN_KEY.with(|slot| {
-        match slot.borrow_mut().as_mut() {
-            Some(ctx) => ctx.push(s),
-            None => {}
+        if let Some(ctx) = slot.borrow_mut().as_mut() {
+            ctx.push(s)
         }
     });
     _InsnCtxt {
@@ -198,9 +197,8 @@ fn get_extern_rust_fn<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
                                 name: &str,
                                 did: DefId)
                                 -> ValueRef {
-    match ccx.externs().borrow().get(name) {
-        Some(n) => return *n,
-        None => (),
+    if let Some(n) = ccx.externs().borrow().get(name) {
+        return *n;
     }
 
     let f = declare::declare_rust_fn(ccx, name, fn_ty);
@@ -238,9 +236,8 @@ pub fn get_extern_const<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
                                   -> ValueRef {
     let name = ccx.sess().cstore.item_symbol(did);
     let ty = type_of(ccx, t);
-    match ccx.externs().borrow_mut().get(&name) {
-        Some(n) => return *n,
-        None => (),
+    if let Some(n) = ccx.externs().borrow_mut().get(&name) {
+        return *n;
     }
     // FIXME(nagisa): perhaps the map of externs could be offloaded to llvm somehow?
     // FIXME(nagisa): investigate whether it can be changed into define_global
@@ -2755,9 +2752,8 @@ fn contains_null(s: &str) -> bool {
 pub fn get_item_val(ccx: &CrateContext, id: ast::NodeId) -> ValueRef {
     debug!("get_item_val(id=`{}`)", id);
 
-    match ccx.item_vals().borrow().get(&id).cloned() {
-        Some(v) => return v,
-        None => {}
+    if let Some(v) = ccx.item_vals().borrow().get(&id).cloned() {
+        return v;
     }
 
     let item = ccx.tcx().map.get(id);

src/librustc_trans/trans/common.rs

@@ -947,9 +947,8 @@ pub fn C_u8(ccx: &CrateContext, i: u8) -> ValueRef {
 // our boxed-and-length-annotated strings.
 pub fn C_cstr(cx: &CrateContext, s: InternedString, null_terminated: bool) -> ValueRef {
     unsafe {
-        match cx.const_cstr_cache().borrow().get(&s) {
-            Some(&llval) => return llval,
-            None => ()
+        if let Some(&llval) = cx.const_cstr_cache().borrow().get(&s) {
+            return llval;
         }
 
         let sc = llvm::LLVMConstStringInContext(cx.llcx(),

src/librustc_trans/trans/type_of.rs

@@ -182,9 +182,8 @@ pub fn type_of_fn_from_ty<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>, fty: Ty<'tcx>)
 //     recursive types. For example, enum types rely on this behavior.
 
 pub fn sizing_type_of<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>, t: Ty<'tcx>) -> Type {
-    match cx.llsizingtypes().borrow().get(&t).cloned() {
-        Some(t) => return t,
-        None => ()
+    if let Some(t) = cx.llsizingtypes().borrow().get(&t).cloned() {
+        return t;
     }
 
     debug!("sizing_type_of {:?}", t);
@@ -317,9 +316,8 @@ pub fn type_of<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>, ty: Ty<'tcx>) -> Type {
 /// NB: If you update this, be sure to update `sizing_type_of()` as well.
 pub fn in_memory_type_of<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>, t: Ty<'tcx>) -> Type {
     // Check the cache.
-    match cx.lltypes().borrow().get(&t) {
-        Some(&llty) => return llty,
-        None => ()
+    if let Some(&llty) = cx.lltypes().borrow().get(&t) {
+        return llty;
     }
 
     debug!("type_of {:?}", t);