Rollup merge of #109582 - scottmcm:local-ref-pending, r=oli-obk

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

As I was reading through this, I noticed that almost every place that was using this needed to distinguish between Some vs None in the match arm anyway, so thought that separating the cases at the variant level might be clearer instead.

I like how it ended up; let me know what you think!

7 files changed, 26 insertions, 20 deletions

diff --git a/compiler/rustc_codegen_ssa/src/mir/block.rs b/compiler/rustc_codegen_ssa/src/mir/block.rs
index 5da0e826c56..2d647f5d7f2 100644
--- a/compiler/rustc_codegen_ssa/src/mir/block.rs
+++ b/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);
             }
         }
diff --git a/compiler/rustc_codegen_ssa/src/mir/debuginfo.rs b/compiler/rustc_codegen_ssa/src/mir/debuginfo.rs
index 6e32c28a42c..d15774696a5 100644
--- a/compiler/rustc_codegen_ssa/src/mir/debuginfo.rs
+++ b/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());
diff --git a/compiler/rustc_codegen_ssa/src/mir/mod.rs b/compiler/rustc_codegen_ssa/src/mir/mod.rs
index 5cffca5230a..189549953d9 100644
--- a/compiler/rustc_codegen_ssa/src/mir/mod.rs
+++ b/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));
diff --git a/compiler/rustc_codegen_ssa/src/mir/operand.rs b/compiler/rustc_codegen_ssa/src/mir/operand.rs
index 25721f75583..b45e7c834e7 100644
--- a/compiler/rustc_codegen_ssa/src/mir/operand.rs
+++ b/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(..) => {
diff --git a/compiler/rustc_codegen_ssa/src/mir/place.rs b/compiler/rustc_codegen_ssa/src/mir/place.rs
index f6523a448e3..1633cfef19d 100644
--- a/compiler/rustc_codegen_ssa/src/mir/place.rs
+++ b/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 {
diff --git a/compiler/rustc_codegen_ssa/src/mir/rvalue.rs b/compiler/rustc_codegen_ssa/src/mir/rvalue.rs
index 4bc4fdab59e..d867d6b0cd4 100644
--- a/compiler/rustc_codegen_ssa/src/mir/rvalue.rs
+++ b/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);
diff --git a/compiler/rustc_codegen_ssa/src/mir/statement.rs b/compiler/rustc_codegen_ssa/src/mir/statement.rs
index 41f585f7fcc..3fd7397ad38 100644
--- a/compiler/rustc_codegen_ssa/src/mir/statement.rs
+++ b/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,