Move default blocks into jump tables (#5756)

Move the default block off of the br_table instrution, and into the JumpTable that it references.

cranelift/frontend/src/frontend.rs

@@ -129,9 +129,7 @@ impl<'short, 'long> InstBuilderBase<'short> for FuncInstBuilder<'short, 'long> {
                 }
             }
 
-            ir::InstructionData::BranchTable {
-                table, destination, ..
-            } => {
+            ir::InstructionData::BranchTable { table, .. } => {
                 // Unlike all other jumps/branches, jump tables are
                 // capable of having the same successor appear
                 // multiple times, so we must deduplicate.
@@ -144,9 +142,12 @@ impl<'short, 'long> InstBuilderBase<'short> for FuncInstBuilder<'short, 'long> {
                     .jump_tables
                     .get(*table)
                     .expect("you are referencing an undeclared jump table")
-                    .iter()
-                    .filter(|&dest_block| unique.insert(*dest_block))
+                    .all_branches()
                 {
+                    if !unique.insert(*dest_block) {
+                        continue;
+                    }
+
                     // Call `declare_block_predecessor` instead of `declare_successor` for
                     // avoiding the borrow checker.
                     self.builder
@@ -154,7 +155,6 @@ impl<'short, 'long> InstBuilderBase<'short> for FuncInstBuilder<'short, 'long> {
                         .ssa
                         .declare_block_predecessor(*dest_block, inst);
                 }
-                self.builder.declare_successor(*destination, inst);
             }
 
             inst => debug_assert!(!inst.opcode().is_branch()),

cranelift/frontend/src/ssa.rs

@@ -591,27 +591,18 @@ impl SSABuilder {
                 }
                 None
             }
-            InstructionData::BranchTable {
-                table: jt,
-                destination,
-                ..
-            } => {
+            InstructionData::BranchTable { table: jt, .. } => {
                 // In the case of a jump table, the situation is tricky because br_table doesn't
                 // support arguments. We have to split the critical edge.
                 let middle_block = dfg.blocks.add();
                 func.stencil.layout.append_block(middle_block);
 
-                let table = &mut dfg.jump_tables[*jt];
-                for block in table.iter_mut() {
+                for block in dfg.jump_tables[*jt].all_branches_mut() {
                     if *block == dest_block {
                         *block = middle_block;
                     }
                 }
 
-                if *destination == dest_block {
-                    *destination = middle_block;
-                }
-
                 let mut cur = FuncCursor::new(func).at_bottom(middle_block);
                 let middle_jump_inst = cur.ins().jump(dest_block, &[val]);
                 Some((middle_block, middle_jump_inst))
@@ -1001,9 +992,6 @@ mod tests {
         let block0 = func.dfg.make_block();
         let block1 = func.dfg.make_block();
         let block2 = func.dfg.make_block();
-        let mut jump_table = JumpTableData::new();
-        jump_table.push_entry(block2);
-        jump_table.push_entry(block1);
         {
             let mut cur = FuncCursor::new(&mut func);
             cur.insert_block(block0);
@@ -1022,9 +1010,10 @@ mod tests {
         ssa.def_var(x_var, x1, block0);
         ssa.use_var(&mut func, x_var, I32, block0).0;
         let br_table = {
+            let jump_table = JumpTableData::new(block2, vec![block2, block1]);
             let jt = func.create_jump_table(jump_table);
             let mut cur = FuncCursor::new(&mut func).at_bottom(block0);
-            cur.ins().br_table(x1, block2, jt)
+            cur.ins().br_table(x1, jt)
         };
 
         // block1

cranelift/frontend/src/switch.rs

@@ -220,7 +220,7 @@ impl Switch {
             "Jump tables bigger than 2^32-1 are not yet supported"
         );
 
-        let jt_data = JumpTableData::with_blocks(Vec::from(blocks));
+        let jt_data = JumpTableData::new(otherwise, Vec::from(blocks));
         let jump_table = bx.create_jump_table(jt_data);
 
         let discr = if first_index == 0 {
@@ -256,7 +256,7 @@ impl Switch {
             _ => discr,
         };
 
-        bx.ins().br_table(discr, otherwise, jump_table);
+        bx.ins().br_table(discr, jump_table);
     }
 
     /// Build the switch