Commit `8fbae77770`

LemonBoy <thatlemon@gmail.com>

2019-09-07 11:17:12

Force LLVM to generate byte-aligned packed unions

Sometimes the frontend and LLVM would disagree on the ABI alignment of a packed union. Solve the problem by telling LLVM we're gonna manage the struct layout by ourselves. Closes #3184

master

1 parent a06f84f

Changed files (2)

src

analyze.cpp

test

stage1

behavior

union.zig

@@ -7905,6 +7905,8 @@ static void resolve_llvm_types_enum(CodeGen *g, ZigType *enum_type, ResolveStatu
 static void resolve_llvm_types_union(CodeGen *g, ZigType *union_type, ResolveStatus wanted_resolve_status) {
     if (union_type->data.unionation.resolve_status >= wanted_resolve_status) return;
 
+    bool packed = (union_type->data.unionation.layout == ContainerLayoutPacked);
+
     TypeUnionField *most_aligned_union_member = union_type->data.unionation.most_aligned_union_member;
     ZigType *tag_type = union_type->data.unionation.tag_type;
     uint32_t gen_field_count = union_type->data.unionation.gen_field_count;
@@ -7971,9 +7973,9 @@ static void resolve_llvm_types_union(CodeGen *g, ZigType *union_type, ResolveSta
                 most_aligned_union_member->type_entry->llvm_type,
                 get_llvm_type(g, padding_array),
             };
-            LLVMStructSetBody(union_type->llvm_type, union_element_types, 2, false);
+            LLVMStructSetBody(union_type->llvm_type, union_element_types, 2, packed);
         } else {
-            LLVMStructSetBody(union_type->llvm_type, &most_aligned_union_member->type_entry->llvm_type, 1, false);
+            LLVMStructSetBody(union_type->llvm_type, &most_aligned_union_member->type_entry->llvm_type, 1, packed);
         }
         union_type->data.unionation.union_llvm_type = union_type->llvm_type;
         union_type->data.unionation.gen_tag_index = SIZE_MAX;
@@ -8012,7 +8014,7 @@ static void resolve_llvm_types_union(CodeGen *g, ZigType *union_type, ResolveSta
     LLVMTypeRef root_struct_element_types[2];
     root_struct_element_types[union_type->data.unionation.gen_tag_index] = get_llvm_type(g, tag_type);
     root_struct_element_types[union_type->data.unionation.gen_union_index] = union_type_ref;
-    LLVMStructSetBody(union_type->llvm_type, root_struct_element_types, 2, false);
+    LLVMStructSetBody(union_type->llvm_type, root_struct_element_types, 2, packed);
 
     // create debug type for union
     ZigLLVMDIType *union_di_type = ZigLLVMCreateDebugUnionType(g->dbuilder,

@@ -482,3 +482,15 @@ test "comparison between union and enum literal" {
     testComparison();
     comptime testComparison();
 }
+
+test "packed union generates correctly aligned LLVM type" {
+    const U = packed union {
+        f1: fn () void,
+        f2: u32,
+    };
+    var foo = [_]U{
+        U{ .f1 = doTest },
+        U{ .f2 = 0 },
+    };
+    foo[0].f1();
+}

Commit 8fbae77770

Commit `8fbae77770`