Refactor BranchInfo::Table to no longer have an optional default branch (#5593)

cranelift/codegen/src/dominator_tree.rs

@@ -360,9 +360,7 @@ impl DominatorTree {
                     for succ in func.jump_tables[jt].iter() {
                         self.push_if_unseen(*succ);
                     }
-                    if let Some(dest) = dest {
-                        self.push_if_unseen(dest);
-                    }
+                    self.push_if_unseen(dest);
                 }
                 BranchInfo::NotABranch => {}
             }

cranelift/codegen/src/flowgraph.rs

@@ -126,9 +126,8 @@ impl ControlFlowGraph {
                     self.add_edge(block, inst, dest.block(&func.dfg.value_lists));
                 }
                 BranchInfo::Table(jt, dest) => {
-                    if let Some(dest) = dest {
-                        self.add_edge(block, inst, dest);
-                    }
+                    self.add_edge(block, inst, dest);
+
                     for dest in func.jump_tables[jt].iter() {
                         self.add_edge(block, inst, *dest);
                     }

cranelift/codegen/src/inst_predicates.rs

@@ -169,12 +169,11 @@ fn visit_branch_targets<F: FnMut(Inst, Block, bool)>(f: &Function, inst: Inst, v
         BranchInfo::SingleDest(dest) => {
             visit(inst, dest.block(&f.dfg.value_lists), false);
         }
-        BranchInfo::Table(table, maybe_dest) => {
-            if let Some(dest) = maybe_dest {
-                // The default block is reached via a direct conditional branch,
-                // so it is not part of the table.
-                visit(inst, dest, false);
-            }
+        BranchInfo::Table(table, dest) => {
+            // The default block is reached via a direct conditional branch,
+            // so it is not part of the table.
+            visit(inst, dest, false);
+
             for &dest in f.jump_tables[table].as_slice() {
                 visit(inst, dest, true);
             }

cranelift/codegen/src/ir/function.rs

@@ -308,7 +308,7 @@ impl FunctionStencil {
                     }
                 });
 
-                if default_dest == Some(old_dest) {
+                if default_dest == old_dest {
                     match &mut self.dfg.insts[inst] {
                         InstructionData::BranchTable { destination, .. } => {
                             *destination = new_dest;

cranelift/codegen/src/ir/instructions.rs

@@ -273,7 +273,7 @@ impl InstructionData {
             Self::Branch { destination, .. } => BranchInfo::SingleDest(destination),
             Self::BranchTable {
                 table, destination, ..
-            } => BranchInfo::Table(table, Some(destination)),
+            } => BranchInfo::Table(table, destination),
             _ => {
                 debug_assert!(!self.opcode().is_branch());
                 BranchInfo::NotABranch
@@ -456,8 +456,8 @@ pub enum BranchInfo {
     /// This is a branch or jump to a single destination block, possibly taking value arguments.
     SingleDest(BlockCall),
 
-    /// This is a jump table branch which can have many destination blocks and maybe one default block.
-    Table(JumpTable, Option<Block>),
+    /// This is a jump table branch which can have many destination blocks and one default block.
+    Table(JumpTable, Block),
 }
 
 /// Information about call instructions.

cranelift/codegen/src/verifier/mod.rs

@@ -1304,18 +1304,16 @@ impl<'a> Verifier<'a> {
                 self.typecheck_variable_args_iterator(inst, iter, args, errors)?;
             }
             BranchInfo::Table(table, block) => {
-                if let Some(block) = block {
-                    let arg_count = self.func.dfg.num_block_params(block);
-                    if arg_count != 0 {
-                        return errors.nonfatal((
-                            inst,
-                            self.context(inst),
-                            format!(
-                                "takes no arguments, but had target {} with {} arguments",
-                                block, arg_count,
-                            ),
-                        ));
-                    }
+                let arg_count = self.func.dfg.num_block_params(block);
+                if arg_count != 0 {
+                    return errors.nonfatal((
+                        inst,
+                        self.context(inst),
+                        format!(
+                            "takes no arguments, but had target {} with {} arguments",
+                            block, arg_count,
+                        ),
+                    ));
                 }
                 for block in self.func.jump_tables[table].iter() {
                     let arg_count = self.func.dfg.num_block_params(*block);