From a917b105a1140533f65fbb3f51b0d21723c4750d Mon Sep 17 00:00:00 2001
From: Veikka Tuominen <git@vexu.eu>
Date: Sat, 19 Mar 2022 00:56:37 +0200
Subject: [PATCH] AstGen: always add dbg_block_end before last instruction

---
 src/AstGen.zig           | 26 +++++++++++++++-----------
 test/behavior/struct.zig |  2 ++
 2 files changed, 17 insertions(+), 11 deletions(-)

diff --git a/src/AstGen.zig b/src/AstGen.zig
index 76dc63032780..8e6540c980f5 100644
--- a/src/AstGen.zig
+++ b/src/AstGen.zig
@@ -6155,11 +6155,11 @@ fn switchExpr(
             }
             const case_result = try expr(&case_scope, sub_scope, block_scope.break_result_loc, case.ast.target_expr);
             try checkUsed(parent_gz, &case_scope.base, sub_scope);
+            try case_scope.addDbgBlockEnd();
             if (!parent_gz.refIsNoReturn(case_result)) {
                 block_scope.break_count += 1;
                 _ = try case_scope.addBreak(.@"break", switch_block, case_result);
             }
-            try case_scope.addDbgBlockEnd();
 
             const case_slice = case_scope.instructionsSlice();
             payloads.items[body_len_index] = @intCast(u32, case_slice.len);
@@ -10874,18 +10874,22 @@ const GenZir = struct {
 
     fn addDbgBlockEnd(gz: *GenZir) !void {
         if (gz.force_comptime) return;
+        const gpa = gz.astgen.gpa;
 
-        if (gz.endsWithNoReturn()) {
-            const last = gz.instructions.pop();
-            _ = try gz.add(.{ .tag = .extended, .data = .{
-                .extended = .{ .opcode = .dbg_block_end, .small = undefined, .operand = undefined },
-            } });
-            try gz.instructions.append(gz.astgen.gpa, last);
-        } else {
-            _ = try gz.add(.{ .tag = .extended, .data = .{
-                .extended = .{ .opcode = .dbg_block_end, .small = undefined, .operand = undefined },
-            } });
+        const tags = gz.astgen.instructions.items(.tag);
+        const data = gz.astgen.instructions.items(.data);
+        const last_inst = gz.instructions.items[gz.instructions.items.len - 1];
+        // remove dbg_block_begin immediately followed by dbg_block_end
+        if (tags[last_inst] == .extended and data[last_inst].extended.opcode == .dbg_block_begin) {
+            _ = gz.instructions.pop();
+            return;
         }
+
+        const new_index = @intCast(Zir.Inst.Index, gz.astgen.instructions.len);
+        try gz.astgen.instructions.append(gpa, .{ .tag = .extended, .data = .{
+            .extended = .{ .opcode = .dbg_block_end, .small = undefined, .operand = undefined },
+        } });
+        try gz.instructions.insert(gpa, gz.instructions.items.len - 1, new_index);
     }
 
     /// Control flow does not fall through the "then" block of a loop; it continues
diff --git a/test/behavior/struct.zig b/test/behavior/struct.zig
index da7d1d74206e..52116ec15882 100644
--- a/test/behavior/struct.zig
+++ b/test/behavior/struct.zig
@@ -427,6 +427,7 @@ test "packed struct 24bits" {
     if (builtin.zig_backend == .stage2_arm) return error.SkipZigTest; // TODO
     if (builtin.zig_backend == .stage2_x86_64) return error.SkipZigTest; // TODO
     if (builtin.cpu.arch == .wasm32) return error.SkipZigTest; // TODO
+    if (builtin.cpu.arch == .arm) return error.SkipZigTest; // TODO
 
     comptime {
         try expect(@sizeOf(Foo24Bits) == 4);
@@ -979,6 +980,7 @@ test "tuple assigned to variable" {
 
 test "comptime struct field" {
     if (builtin.zig_backend == .stage2_arm) return error.SkipZigTest; // TODO
+    if (builtin.stage2_arch == .arm) return error.SkipZigTest; // TODO
 
     const T = struct {
         a: i32,