Sema: const inferred alloc infers comptime-ness

const locals now detect if the value ends up being comptime known. In
such case, it replaces the runtime AIR instructions with a decl_ref
const.

In the backends, some more sophisticated logic for marking decls as
alive was needed to prevent Decls incorrectly being garbage collected
that were indirectly referenced in such manner.

1 files changed, 14 insertions, 1 deletions

diff --git a/src/codegen/c.zig b/src/codegen/c.zig
index 191be36494..922e1d9c3e 100644
--- a/src/codegen/c.zig
+++ b/src/codegen/c.zig
@@ -195,7 +195,7 @@ pub const DeclGen = struct {
         val: Value,
         decl: *Decl,
     ) error{ OutOfMemory, AnalysisFail }!void {
-        decl.alive = true;
+        markDeclAlive(decl);
 
         if (ty.isSlice()) {
             try writer.writeByte('(');
@@ -227,6 +227,19 @@ pub const DeclGen = struct {
         try dg.renderDeclName(decl, writer);
     }
 
+    fn markDeclAlive(decl: *Decl) void {
+        if (decl.alive) return;
+        decl.alive = true;
+
+        // This is the first time we are marking this Decl alive. We must
+        // therefore recurse into its value and mark any Decl it references
+        // as also alive, so that any Decl referenced does not get garbage collected.
+
+        if (decl.val.pointerDecl()) |pointee| {
+            return markDeclAlive(pointee);
+        }
+    }
+
     fn renderInt128(
         writer: anytype,
         int_val: anytype,