7 - Make more use of let_chains

Continuation of #94376.

cc #53667

compiler/rustc_mir_transform/src/const_debuginfo.rs

@@ -55,12 +55,10 @@ fn find_optimization_oportunities<'tcx>(body: &Body<'tcx>) -> Vec<(Local, Consta
 
     let mut locals_to_debuginfo = BitSet::new_empty(body.local_decls.len());
     for debuginfo in &body.var_debug_info {
-        if let VarDebugInfoContents::Place(p) = debuginfo.value {
+        if let VarDebugInfoContents::Place(p) = debuginfo.value && let Some(l) = p.as_local() {
-            if let Some(l) = p.as_local() {
             locals_to_debuginfo.insert(l);
         }
     }
-    }
 
     let mut eligable_locals = Vec::new();
     for (local, mutating_uses) in visitor.local_mutating_uses.drain_enumerated(..) {

compiler/rustc_mir_transform/src/const_prop.rs

@@ -633,8 +633,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
     fn propagate_operand(&mut self, operand: &mut Operand<'tcx>) {
         match *operand {
             Operand::Copy(l) | Operand::Move(l) => {
-                if let Some(value) = self.get_const(l) {
+                if let Some(value) = self.get_const(l) && self.should_const_prop(&value) {
-                    if self.should_const_prop(&value) {
                     // FIXME(felix91gr): this code only handles `Scalar` cases.
                     // For now, we're not handling `ScalarPair` cases because
                     // doing so here would require a lot of code duplication.
@@ -653,7 +652,6 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
                     }
                 }
             }
-            }
             Operand::Constant(_) => (),
         }
     }
@@ -1086,8 +1084,7 @@ impl<'tcx> MutVisitor<'tcx> for ConstPropagator<'_, 'tcx> {
                 // This will return None if the above `const_prop` invocation only "wrote" a
                 // type whose creation requires no write. E.g. a generator whose initial state
                 // consists solely of uninitialized memory (so it doesn't capture any locals).
-                if let Some(ref value) = self.get_const(place) {
+                if let Some(ref value) = self.get_const(place) && self.should_const_prop(value) {
-                    if self.should_const_prop(value) {
                     trace!("replacing {:?} with {:?}", rval, value);
                     self.replace_with_const(rval, value, source_info);
                     if can_const_prop == ConstPropMode::FullConstProp
@@ -1096,7 +1093,6 @@ impl<'tcx> MutVisitor<'tcx> for ConstPropagator<'_, 'tcx> {
                         trace!("propagated into {:?}", place);
                     }
                 }
-                }
                 match can_const_prop {
                     ConstPropMode::OnlyInsideOwnBlock => {
                         trace!(

compiler/rustc_mir_transform/src/coverage/debug.rs

@@ -357,15 +357,13 @@ impl DebugCounters {
         if let Some(counters) = &self.some_counters {
             if let Some(DebugCounter { counter_kind, some_block_label }) = counters.get(&operand) {
                 if let CoverageKind::Expression { .. } = counter_kind {
-                    if let Some(block_label) = some_block_label {
+                    if let Some(label) = some_block_label && debug_options().counter_format.block {
-                        if debug_options().counter_format.block {
                         return format!(
                             "{}:({})",
-                                block_label,
+                            label,
                             self.format_counter_kind(counter_kind)
                         );
                     }
-                    }
                     return format!("({})", self.format_counter_kind(counter_kind));
                 }
                 return self.format_counter_kind(counter_kind);

compiler/rustc_mir_transform/src/coverage/spans.rs

@@ -191,17 +191,14 @@ impl CoverageSpan {
     /// If the span is part of a macro, and the macro is visible (expands directly to the given
     /// body_span), returns the macro name symbol.
     pub fn visible_macro(&self, body_span: Span) -> Option<Symbol> {
-        if let Some(current_macro) = self.current_macro() {
+        if let Some(current_macro) = self.current_macro() && self
-            if self
             .expn_span
             .parent_callsite()
             .unwrap_or_else(|| bug!("macro must have a parent"))
-                .ctxt()
+            .ctxt() == body_span.ctxt()
-                == body_span.ctxt()
         {
             return Some(current_macro);
         }
-        }
         None
     }
 
@@ -584,8 +581,7 @@ impl<'a, 'tcx> CoverageSpans<'a, 'tcx> {
     /// In either case, no more spans will match the span of `pending_dups`, so
     /// add the `pending_dups` if they don't overlap `curr`, and clear the list.
     fn check_pending_dups(&mut self) {
-        if let Some(dup) = self.pending_dups.last() {
+        if let Some(dup) = self.pending_dups.last() && dup.span != self.prev().span {
-            if dup.span != self.prev().span {
             debug!(
                 "    SAME spans, but pending_dups are NOT THE SAME, so BCBs matched on \
                 previous iteration, or prev started a new disjoint span"
@@ -601,7 +597,6 @@ impl<'a, 'tcx> CoverageSpans<'a, 'tcx> {
             }
         }
     }
-    }
 
     /// Advance `prev` to `curr` (if any), and `curr` to the next `CoverageSpan` in sorted order.
     fn next_coverage_span(&mut self) -> bool {

compiler/rustc_mir_transform/src/dest_prop.rs

@@ -549,8 +549,10 @@ impl<'a> Conflicts<'a> {
                 target: _,
                 unwind: _,
             } => {
-                if let Some(place) = value.place() {
+                if let Some(place) = value.place()
-                    if !place.is_indirect() && !dropped_place.is_indirect() {
+                    && !place.is_indirect()
+                    && !dropped_place.is_indirect()
+                {
                     self.record_local_conflict(
                         place.local,
                         dropped_place.local,
@@ -558,7 +560,6 @@ impl<'a> Conflicts<'a> {
                     );
                 }
             }
-            }
             TerminatorKind::Yield { value, resume: _, resume_arg, drop: _ } => {
                 if let Some(place) = value.place() {
                     if !place.is_indirect() && !resume_arg.is_indirect() {
@@ -614,8 +615,10 @@ impl<'a> Conflicts<'a> {
                             for op in operands {
                                 match op {
                                     InlineAsmOperand::In { reg: _, value } => {
-                                        if let Some(p) = value.place() {
+                                        if let Some(p) = value.place()
-                                            if !p.is_indirect() && !dest_place.is_indirect() {
+                                            && !p.is_indirect()
+                                            && !dest_place.is_indirect()
+                                        {
                                             self.record_local_conflict(
                                                 p.local,
                                                 dest_place.local,
@@ -623,7 +626,6 @@ impl<'a> Conflicts<'a> {
                                             );
                                         }
                                     }
-                                    }
                                     InlineAsmOperand::Out {
                                         reg: _,
                                         late: _,
@@ -643,18 +645,21 @@ impl<'a> Conflicts<'a> {
                                         in_value,
                                         out_place,
                                     } => {
-                                        if let Some(place) = in_value.place() {
+                                        if let Some(place) = in_value.place()
-                                            if !place.is_indirect() && !dest_place.is_indirect() {
+                                            && !place.is_indirect()
+                                            && !dest_place.is_indirect()
+                                        {
                                             self.record_local_conflict(
                                                 place.local,
                                                 dest_place.local,
                                                 "asm! operand overlap",
                                             );
                                         }
-                                        }
 
-                                        if let Some(place) = out_place {
+                                        if let Some(place) = out_place
-                                            if !place.is_indirect() && !dest_place.is_indirect() {
+                                            && !place.is_indirect()
+                                            && !dest_place.is_indirect()
+                                        {
                                             self.record_local_conflict(
                                                 place.local,
                                                 dest_place.local,
@@ -662,7 +667,6 @@ impl<'a> Conflicts<'a> {
                                             );
                                         }
                                     }
-                                    }
                                     InlineAsmOperand::Out { reg: _, late: _, place: None }
                                     | InlineAsmOperand::Const { value: _ }
                                     | InlineAsmOperand::SymFn { value: _ }

compiler/rustc_mir_transform/src/inline.rs

@@ -724,13 +724,12 @@ impl<'tcx> Inliner<'tcx> {
         caller_body: &mut Body<'tcx>,
     ) -> Local {
         // Reuse the operand if it is a moved temporary.
-        if let Operand::Move(place) = &arg {
+        if let Operand::Move(place) = &arg
-            if let Some(local) = place.as_local() {
+            && let Some(local) = place.as_local()
-                if caller_body.local_kind(local) == LocalKind::Temp {
+            && caller_body.local_kind(local) == LocalKind::Temp
+        {
             return local;
         }
-            }
-        }
 
         // Otherwise, create a temporary for the argument.
         trace!("creating temp for argument {:?}", arg);

compiler/rustc_mir_transform/src/instcombine.rs

@@ -77,12 +77,10 @@ impl<'tcx> InstCombineContext<'tcx, '_> {
                     _ => None,
                 };
 
-                if let Some(new) = new {
+                if let Some(new) = new && self.should_combine(source_info, rvalue) {
-                    if self.should_combine(source_info, rvalue) {
                     *rvalue = new;
                 }
             }
-            }
 
             _ => {}
         }

compiler/rustc_mir_transform/src/lib.rs

@@ -1,16 +1,17 @@
+#![allow(rustc::potential_query_instability)]
 #![feature(box_patterns)]
 #![feature(box_syntax)]
 #![feature(crate_visibility_modifier)]
+#![feature(let_chains)]
 #![feature(let_else)]
 #![feature(map_try_insert)]
 #![feature(min_specialization)]
-#![feature(option_get_or_insert_default)]
-#![feature(once_cell)]
 #![feature(never_type)]
+#![feature(once_cell)]
+#![feature(option_get_or_insert_default)]
 #![feature(trusted_step)]
 #![feature(try_blocks)]
 #![recursion_limit = "256"]
-#![allow(rustc::potential_query_instability)]
 
 #[macro_use]
 extern crate tracing;

compiler/rustc_mir_transform/src/required_consts.rs

@@ -14,10 +14,9 @@ impl<'a, 'tcx> RequiredConstsVisitor<'a, 'tcx> {
 
 impl<'tcx> Visitor<'tcx> for RequiredConstsVisitor<'_, 'tcx> {
     fn visit_constant(&mut self, constant: &Constant<'tcx>, _: Location) {
-        if let Some(ct) = constant.literal.const_for_ty() {
+        let literal = constant.literal;
-            if let ConstKind::Unevaluated(_) = ct.val() {
+        if let Some(ct) = literal.const_for_ty() && let ConstKind::Unevaluated(_) = ct.val() {
             self.required_consts.push(*constant);
         }
     }
-    }
 }