From 26dc88e096fd523bf4c71ceefc53e860f25d51b1 Mon Sep 17 00:00:00 2001
From: Christoffer Lerno <christoffer@aegik.com>
Date: Sun, 26 Jan 2025 15:38:24 +0100
Subject: [PATCH] Fix issues with @jump on empty `default` or only `default`
 #1893 #1894

---
 releasenotes.md                      |  2 +-
 src/compiler/llvm_codegen_stmt.c     |  4 +-
 src/compiler/sema_stmts.c            |  6 ++-
 test/test_suite/switch/jump_bugs.c3t | 70 ++++++++++++++++++++++++++++
 4 files changed, 79 insertions(+), 3 deletions(-)
 create mode 100644 test/test_suite/switch/jump_bugs.c3t

diff --git a/releasenotes.md b/releasenotes.md
index 3489cb9b8..678034bbb 100644
--- a/releasenotes.md
+++ b/releasenotes.md
@@ -29,7 +29,7 @@
 - Fix bug where .min/.max would fail on a distinct int #1888.
 - Fix issue where compile time declarations in expression list would not be handled properly.
 - Issue where trailing body argument was allowed without type even though the definition specified it #1879.
-
+- Fix issues with @jump on empty `default` or only `default` #1893 #1894
 ### Stdlib changes
 - Added '%h' and '%H' for printing out binary data in hexadecimal using the formatter.
 - Added weakly linked `__powidf2`
diff --git a/src/compiler/llvm_codegen_stmt.c b/src/compiler/llvm_codegen_stmt.c
index bc0244009..86ee59bbd 100644
--- a/src/compiler/llvm_codegen_stmt.c
+++ b/src/compiler/llvm_codegen_stmt.c
@@ -777,6 +777,7 @@ static LLVMValueRef llvm_emit_switch_jump_stmt(GenContext *c,
 									   LLVMBasicBlockRef default_block,
 									   BEValue *switch_value)
 {
+	ASSERT_SPAN(switch_ast, min_index > -1);
 	unsigned case_count = vec_size(cases);
 	BEValue min_val;
 	llvm_emit_expr(c, &min_val, exprptr(cases[min_index]->case_stmt.expr));
@@ -848,6 +849,7 @@ static void llvm_emit_switch_jump_table(GenContext *c,
 		Ast *case_ast = cases[i];
 		if (case_ast->ast_kind == AST_DEFAULT_STMT)
 		{
+			if (!case_ast->case_stmt.body) continue;
 			default_block = case_ast->case_stmt.backend_block;
 			default_index = i;
 			continue;
@@ -914,7 +916,7 @@ static void llvm_emit_switch_jump_table(GenContext *c,
 			if (!case_stmt->case_stmt.body) continue;
 			LLVMAddDestination(instr, block);
 		}
-
+		if (!case_stmt->case_stmt.body) continue;
 		llvm_emit_block(c, block);
 		llvm_emit_stmt(c, case_stmt->case_stmt.body);
 		llvm_emit_br(c, exit_block);
diff --git a/src/compiler/sema_stmts.c b/src/compiler/sema_stmts.c
index 172df67a2..a15dad0cb 100644
--- a/src/compiler/sema_stmts.c
+++ b/src/compiler/sema_stmts.c
@@ -2533,7 +2533,11 @@ static bool sema_analyse_switch_body(SemaContext *context, Ast *statement, Sourc
 				RETURN_SEMA_ERROR(statement, "The switch cannot use a jump table size of the table would exceed "
 				                             "the maximum allowed (%u), please remove '@jump'.", compiler.build.switchjump_max_size);
 			}
-
+		}
+		// Do not generate a jump table if we only have a default statement.
+		if (default_case && case_count == 1)
+		{
+			statement->flow.jump = false;
 		}
 	}
 
diff --git a/test/test_suite/switch/jump_bugs.c3t b/test/test_suite/switch/jump_bugs.c3t
new file mode 100644
index 000000000..8947effc0
--- /dev/null
+++ b/test/test_suite/switch/jump_bugs.c3t
@@ -0,0 +1,70 @@
+// #target: macos-aarch64
+module test;
+
+fn void test1()
+{
+	switch (0) @jump
+    {
+        case 0:
+            break;
+        default:
+	}
+}
+
+enum Foo { A, B, }
+
+fn void main()
+{
+	test1();
+	switch (Foo.A) @jump
+	{
+        default:
+			break;
+	}
+}
+
+/* #expect: test.ll
+
+@jumptable = private unnamed_addr constant [1 x ptr] [ptr blockaddress(@test.test1, %switch.case)], align 4
+
+define void @test.test1() #0 {
+entry:
+  %switch = alloca i32, align 4
+  store i32 0, ptr %switch, align 4
+  br label %switch.entry
+
+switch.entry:                                     ; preds = %entry
+  %0 = load i32, ptr %switch, align 4
+  %1 = icmp ugt i32 %0, 0
+  br i1 %1, label %switch.exit, label %jumpblock
+
+jumpblock:                                        ; preds = %switch.entry
+  %ptroffset = getelementptr inbounds [8 x i8], ptr @jumptable, i32 %0
+  %target = load ptr, ptr %ptroffset, align 8
+  indirectbr ptr %target, [label %switch.case]
+
+switch.case:                                      ; preds = %jumpblock
+  br label %switch.exit
+
+switch.exit:                                      ; preds = %switch.case, %switch.entry
+  ret void
+}
+
+define void @test.main() #0 {
+entry:
+  %switch = alloca i32, align 4
+  call void @test.test1()
+  store i32 0, ptr %switch, align 4
+  br label %switch.entry
+
+switch.entry:                                     ; preds = %entry
+  %0 = load i32, ptr %switch, align 4
+  switch i32 %0, label %switch.default [
+  ]
+
+switch.default:                                   ; preds = %switch.entry
+  br label %switch.exit
+
+switch.exit:                                      ; preds = %switch.default
+  ret void
+}