Refactoring of branch ordering and zero-check optimization based on PR feedback.

cranelift/codegen/src/simple_preopt.rs

@@ -566,7 +566,13 @@ fn branch_opt(pos: &mut FuncCursor, inst: Inst) {
                 let args = pos.func.dfg.inst_args(inst);
                 args[0]
             };
+            let iconst_inst =
                 if let ValueDef::Result(iconst_inst, _) = pos.func.dfg.value_def(first_arg) {
+                    iconst_inst
+                } else {
+                    return;
+                };
+
             if let InstructionData::BinaryImm {
                 opcode: Opcode::IfcmpImm,
                 imm: cmp_imm,
@@ -578,25 +584,18 @@ fn branch_opt(pos: &mut FuncCursor, inst: Inst) {
                     return;
                 }
 
-                    match br_cond {
+                let kind = match br_cond {
-                        IntCC::NotEqual => BranchOptInfo {
+                    IntCC::NotEqual => BranchOptKind::NotEqualZero,
-                            br_inst: inst,
+                    IntCC::Equal => BranchOptKind::EqualZero,
-                            cmp_arg: cmp_arg,
-                            destination: destination,
-                            args: args.clone(),
-                            kind: BranchOptKind::NotEqualZero,
-                        },
-                        IntCC::Equal => BranchOptInfo {
-                            br_inst: inst,
-                            cmp_arg: cmp_arg,
-                            destination: destination,
-                            args: args.clone(),
-                            kind: BranchOptKind::EqualZero,
-                        },
                     _ => return,
-                    }
+                };
-                } else {
+
-                    return;
+                BranchOptInfo {
+                    br_inst: inst,
+                    cmp_arg: cmp_arg,
+                    destination: destination,
+                    args: args.clone(),
+                    kind: kind,
                 }
             } else {
                 return;
@@ -648,21 +647,31 @@ fn branch_order(pos: &mut FuncCursor, cfg: &mut ControlFlowGraph, ebb: Ebb, inst
             destination,
             ref args,
         } => {
-            if let Some(next_ebb) = pos.func.layout.next_ebb(ebb) {
+            let next_ebb = if let Some(next_ebb) = pos.func.layout.next_ebb(ebb) {
+                next_ebb
+            } else {
+                return;
+            };
+
             if destination == next_ebb {
                 return;
             }
 
-                if let Some(prev_inst) = pos.func.layout.prev_inst(inst) {
+            let prev_inst = if let Some(prev_inst) = pos.func.layout.prev_inst(inst) {
-                    let prev_inst_data = &pos.func.dfg[prev_inst];
+                prev_inst
-                    if !prev_inst_data.opcode().is_branch() {
+            } else {
                 return;
-                    }
+            };
+
+            let prev_inst_data = &pos.func.dfg[prev_inst];
 
             if let Some(prev_dest) = prev_inst_data.branch_destination() {
                 if prev_dest != next_ebb {
                     return;
                 }
+            } else {
+                return;
+            }
 
             match prev_inst_data {
                 InstructionData::Branch {
@@ -676,28 +685,21 @@ fn branch_order(pos: &mut FuncCursor, cfg: &mut ControlFlowGraph, ebb: Ebb, inst
                         args[0]
                     };
 
-                                match opcode {
+                    let kind = match opcode {
-                                    Opcode::Brz => BranchOrderInfo {
+                        Opcode::Brz => BranchOrderKind::BrzToBrnz,
-                                        term_inst: inst,
+                        Opcode::Brnz => BranchOrderKind::BrnzToBrz,
-                                        term_inst_args: args.clone(),
-                                        term_dest: destination,
-                                        cond_inst: prev_inst,
-                                        cond_arg: cond_arg,
-                                        cond_inst_args: prev_args.clone(),
-                                        cond_dest: *cond_dest,
-                                        kind: BranchOrderKind::BrzToBrnz,
-                                    },
-                                    Opcode::Brnz => BranchOrderInfo {
-                                        term_inst: inst,
-                                        term_inst_args: args.clone(),
-                                        term_dest: destination,
-                                        cond_inst: prev_inst,
-                                        cond_arg: cond_arg,
-                                        cond_inst_args: prev_args.clone(),
-                                        cond_dest: *cond_dest,
-                                        kind: BranchOrderKind::BrnzToBrz,
-                                    },
                         _ => panic!("unexpected opcode"),
+                    };
+
+                    BranchOrderInfo {
+                        term_inst: inst,
+                        term_inst_args: args.clone(),
+                        term_dest: destination,
+                        cond_inst: prev_inst,
+                        cond_arg: cond_arg,
+                        cond_inst_args: prev_args.clone(),
+                        cond_dest: *cond_dest,
+                        kind: kind,
                     }
                 }
                 InstructionData::BranchInt {
@@ -746,16 +748,8 @@ fn branch_order(pos: &mut FuncCursor, cfg: &mut ControlFlowGraph, ebb: Ebb, inst
                 }
                 _ => return,
             }
-                    } else {
-                        return;
-                    }
-                } else {
-                    return;
-                }
-            } else {
-                return;
-            }
         }
+
         _ => return,
     };