From b3bc7f6e644972e94964e155bdc9a1463ed1a6a0 Mon Sep 17 00:00:00 2001
From: Mathias Magnusson <mathias@magnusson.space>
Date: Fri, 1 Aug 2025 17:11:06 +0200
Subject: assert that block ending instructions happen only & exactly at the
 end of each block

---
 src/compile.zig | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/src/compile.zig b/src/compile.zig
index 3ee3eb0..80279fb 100644
--- a/src/compile.zig
+++ b/src/compile.zig
@@ -98,8 +98,13 @@ pub const BasicBlock = struct {
 
     fn finalize(self: *BasicBlock, allocator: Allocator) !void {
         std.debug.assert(self.instrs.items.len > 0);
+        for (self.instrs.items[0 .. self.instrs.items.len - 1]) |instr| {
+            std.debug.assert(switch (instr.type) {
+                inline else => |ty| !@hasDecl(@TypeOf(ty), "ends_block"),
+            });
+        }
         std.debug.assert(switch (self.instrs.getLast().type) {
-            inline else => |ty| @hasDecl(@TypeOf(ty), "may_end_block"),
+            inline else => |ty| @hasDecl(@TypeOf(ty), "ends_block"),
         });
 
         self.vreg_last_use = .empty;
@@ -195,7 +200,7 @@ pub const Instr = struct {
         true: BlockRef,
         false: BlockRef,
 
-        pub const may_end_block = {};
+        pub const ends_block = {};
 
         pub fn sources(_: Branch) Sources {
             return Sources.init(0) catch unreachable;
@@ -205,7 +210,7 @@ pub const Instr = struct {
     pub const Jump = struct {
         to: BlockRef,
 
-        pub const may_end_block = {};
+        pub const ends_block = {};
 
         pub fn sources(_: Jump) Sources {
             return Sources.init(0) catch unreachable;
@@ -233,7 +238,7 @@ pub const Instr = struct {
     pub const Return = struct {
         val: VReg,
 
-        pub const may_end_block = {};
+        pub const ends_block = {};
 
         pub fn sources(self: Return) Sources {
             return Sources.fromSlice(&.{self.val}) catch unreachable;
-- 
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