Refactor: Separate LocalRef variant for not-evaluated-yet operands

Author: scottmcm

compiler/rustc_codegen_ssa/src/mir/block.rs

@@ -397,8 +397,8 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
 
             PassMode::Cast(cast_ty, _) => {
                 let op = match self.locals[mir::RETURN_PLACE] {
-                    LocalRef::Operand(Some(op)) => op,
-                    LocalRef::Operand(None) => bug!("use of return before def"),
+                    LocalRef::Operand(op) => op,
+                    LocalRef::PendingOperand => bug!("use of return before def"),
                     LocalRef::Place(cg_place) => OperandRef {
                         val: Ref(cg_place.llval, None, cg_place.align),
                         layout: cg_place.layout,
@@ -1673,7 +1673,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
             match self.locals[index] {
                 LocalRef::Place(dest) => dest,
                 LocalRef::UnsizedPlace(_) => bug!("return type must be sized"),
-                LocalRef::Operand(None) => {
+                LocalRef::PendingOperand => {
                     // Handle temporary places, specifically `Operand` ones, as
                     // they don't have `alloca`s.
                     return if fn_ret.is_indirect() {
@@ -1694,7 +1694,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                         ReturnDest::DirectOperand(index)
                     };
                 }
-                LocalRef::Operand(Some(_)) => {
+                LocalRef::Operand(_) => {
                     bug!("place local already assigned to");
                 }
             }
@@ -1737,7 +1737,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
             IndirectOperand(tmp, index) => {
                 let op = bx.load_operand(tmp);
                 tmp.storage_dead(bx);
-                self.locals[index] = LocalRef::Operand(Some(op));
+                self.locals[index] = LocalRef::Operand(op);
                 self.debug_introduce_local(bx, index);
             }
             DirectOperand(index) => {
@@ -1752,7 +1752,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 } else {
                     OperandRef::from_immediate_or_packed_pair(bx, llval, ret_abi.layout)
                 };
-                self.locals[index] = LocalRef::Operand(Some(op));
+                self.locals[index] = LocalRef::Operand(op);
                 self.debug_introduce_local(bx, index);
             }
         }

compiler/rustc_codegen_ssa/src/mir/debuginfo.rs

@@ -312,7 +312,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 LocalRef::Place(place) | LocalRef::UnsizedPlace(place) => {
                     bx.set_var_name(place.llval, name);
                 }
-                LocalRef::Operand(Some(operand)) => match operand.val {
+                LocalRef::Operand(operand) => match operand.val {
                     OperandValue::Ref(x, ..) | OperandValue::Immediate(x) => {
                         bx.set_var_name(x, name);
                     }
@@ -323,7 +323,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                         bx.set_var_name(b, &(name.clone() + ".1"));
                     }
                 },
-                LocalRef::Operand(None) => {}
+                LocalRef::PendingOperand => {}
             }
         }
 
@@ -332,9 +332,9 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         }
 
         let base = match local_ref {
-            LocalRef::Operand(None) => return,
+            LocalRef::PendingOperand => return,
 
-            LocalRef::Operand(Some(operand)) => {
+            LocalRef::Operand(operand) => {
                 // Don't spill operands onto the stack in naked functions.
                 // See: https://github.com/rust-lang/rust/issues/42779
                 let attrs = bx.tcx().codegen_fn_attrs(self.instance.def_id());

compiler/rustc_codegen_ssa/src/mir/mod.rs

@@ -123,7 +123,10 @@ enum LocalRef<'tcx, V> {
     /// Every time it is initialized, we have to reallocate the place
     /// and update the fat pointer. That's the reason why it is indirect.
     UnsizedPlace(PlaceRef<'tcx, V>),
-    Operand(Option<OperandRef<'tcx, V>>),
+    /// The backend [`OperandValue`] has already been generated.
+    Operand(OperandRef<'tcx, V>),
+    /// Will be a `Self::Operand` once we get to its definition.
+    PendingOperand,
 }
 
 impl<'a, 'tcx, V: CodegenObject> LocalRef<'tcx, V> {
@@ -135,9 +138,9 @@ impl<'a, 'tcx, V: CodegenObject> LocalRef<'tcx, V> {
             // Zero-size temporaries aren't always initialized, which
             // doesn't matter because they don't contain data, but
             // we need something in the operand.
-            LocalRef::Operand(Some(OperandRef::new_zst(bx, layout)))
+            LocalRef::Operand(OperandRef::new_zst(bx, layout))
         } else {
-            LocalRef::Operand(None)
+            LocalRef::PendingOperand
         }
     }
 }
@@ -337,7 +340,7 @@ fn arg_local_refs<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
                 // We don't have to cast or keep the argument in the alloca.
                 // FIXME(eddyb): We should figure out how to use llvm.dbg.value instead
                 // of putting everything in allocas just so we can use llvm.dbg.declare.
-                let local = |op| LocalRef::Operand(Some(op));
+                let local = |op| LocalRef::Operand(op);
                 match arg.mode {
                     PassMode::Ignore => {
                         return local(OperandRef::new_zst(bx, arg.layout));

compiler/rustc_codegen_ssa/src/mir/operand.rs

@@ -370,7 +370,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         debug!("maybe_codegen_consume_direct(place_ref={:?})", place_ref);
 
         match self.locals[place_ref.local] {
-            LocalRef::Operand(Some(mut o)) => {
+            LocalRef::Operand(mut o) => {
                 // Moves out of scalar and scalar pair fields are trivial.
                 for elem in place_ref.projection.iter() {
                     match elem {
@@ -395,7 +395,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
 
                 Some(o)
             }
-            LocalRef::Operand(None) => {
+            LocalRef::PendingOperand => {
                 bug!("use of {:?} before def", place_ref);
             }
             LocalRef::Place(..) | LocalRef::UnsizedPlace(..) => {

compiler/rustc_codegen_ssa/src/mir/place.rs

@@ -558,6 +558,9 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                     bug!("using operand local {:?} as place", place_ref);
                 }
             }
+            LocalRef::PendingOperand => {
+                bug!("using still-pending operand local {:?} as place", place_ref);
+            }
         };
         for elem in place_ref.projection[base..].iter() {
             cg_base = match *elem {

compiler/rustc_codegen_ssa/src/mir/rvalue.rs

@@ -545,7 +545,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         // ZST are passed as operands and require special handling
         // because codegen_place() panics if Local is operand.
         if let Some(index) = place.as_local() {
-            if let LocalRef::Operand(Some(op)) = self.locals[index] {
+            if let LocalRef::Operand(op) = self.locals[index] {
                 if let ty::Array(_, n) = op.layout.ty.kind() {
                     let n = n.eval_target_usize(bx.cx().tcx(), ty::ParamEnv::reveal_all());
                     return bx.cx().const_usize(n);

compiler/rustc_codegen_ssa/src/mir/statement.rs

@@ -18,12 +18,12 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                         LocalRef::UnsizedPlace(cg_indirect_dest) => {
                             self.codegen_rvalue_unsized(bx, cg_indirect_dest, rvalue)
                         }
-                        LocalRef::Operand(None) => {
+                        LocalRef::PendingOperand => {
                             let operand = self.codegen_rvalue_operand(bx, rvalue);
-                            self.locals[index] = LocalRef::Operand(Some(operand));
+                            self.locals[index] = LocalRef::Operand(operand);
                             self.debug_introduce_local(bx, index);
                         }
-                        LocalRef::Operand(Some(op)) => {
+                        LocalRef::Operand(op) => {
                             if !op.layout.is_zst() {
                                 span_bug!(
                                     statement.source_info.span,