From 01d19a8d3cdd52ad50f45bfb8666b56ccf8d3a22 Mon Sep 17 00:00:00 2001
From: Veikka Tuominen <git@vexu.eu>
Date: Tue, 30 Aug 2022 14:40:48 +0300
Subject: [PATCH] Sema: do not emit generic poison for non generic parameters

Closes #12679
---
 src/Sema.zig                                   | 18 ++++++++++++++++--
 ...n-comptime-parameter-used-as-array-size.zig | 16 ++++++++++++++++
 2 files changed, 32 insertions(+), 2 deletions(-)
 create mode 100644 test/cases/compile_errors/non-comptime-parameter-used-as-array-size.zig

diff --git a/src/Sema.zig b/src/Sema.zig
index 823ae9baf2..bf147a7cb4 100644
--- a/src/Sema.zig
+++ b/src/Sema.zig
@@ -8195,8 +8195,22 @@ fn zirParam(
         .is_comptime = comptime_syntax,
         .name = param_name,
     });
-    const result = try sema.addConstant(param_ty, Value.initTag(.generic_poison));
-    try sema.inst_map.putNoClobber(sema.gpa, inst, result);
+
+    if (is_comptime) {
+        // If this is a comptime parameter we can add a constant generic_poison
+        // since this is also a generic parameter.
+        const result = try sema.addConstant(param_ty, Value.initTag(.generic_poison));
+        try sema.inst_map.putNoClobber(sema.gpa, inst, result);
+    } else {
+        // Otherwise we need a dummy runtime instruction.
+        const result_index = @intCast(Air.Inst.Index, sema.air_instructions.len);
+        try sema.air_instructions.append(sema.gpa, .{
+            .tag = .alloc,
+            .data = .{ .ty = param_ty },
+        });
+        const result = Air.indexToRef(result_index);
+        try sema.inst_map.putNoClobber(sema.gpa, inst, result);
+    }
 }
 
 fn zirParamAnytype(
diff --git a/test/cases/compile_errors/non-comptime-parameter-used-as-array-size.zig b/test/cases/compile_errors/non-comptime-parameter-used-as-array-size.zig
new file mode 100644
index 0000000000..b5495480ed
--- /dev/null
+++ b/test/cases/compile_errors/non-comptime-parameter-used-as-array-size.zig
@@ -0,0 +1,16 @@
+export fn entry() void {
+    const llamas1 = makeLlamas(5);
+    const llamas2 = makeLlamas(5);
+    _ = llamas1;
+    _ = llamas2;
+}
+
+fn makeLlamas(count: usize) [count]u8 {
+    _ = count;
+}
+
+// error
+// target=native
+//
+// :8:30: error: unable to resolve comptime value
+// :8:30: note: array length must be comptime known