stage2: Change optional non-null field to i8

This is a workaround for llvm/llvm-project#56585
which causes writes to i1 in memory to be optimized to an incorrect value.
Unfortunately, this does not save users from running into this bug with u1
in their own types.

However, this does seem to be enough to get the behavior tests working.
This resolves #11450 on my machine.

Author: topolarity

src/codegen/llvm.zig

@@ -1499,7 +1499,7 @@ pub const Object = struct {
                     break :blk fwd_decl;
                 };
 
-                const non_null_ty = Type.bool;
+                const non_null_ty = Type.u8;
                 const payload_size = child_ty.abiSize(target);
                 const payload_align = child_ty.abiAlignment(target);
                 const non_null_size = non_null_ty.abiSize(target);
@@ -2530,16 +2530,16 @@ pub const DeclGen = struct {
                 var buf: Type.Payload.ElemType = undefined;
                 const child_ty = t.optionalChild(&buf);
                 if (!child_ty.hasRuntimeBitsIgnoreComptime()) {
-                    return dg.context.intType(1);
+                    return dg.context.intType(8);
                 }
                 const payload_llvm_ty = try dg.lowerType(child_ty);
                 if (t.optionalReprIsPayload()) {
                     return payload_llvm_ty;
                 }
 
-                comptime assert(optional_layout_version == 2);
+                comptime assert(optional_layout_version == 3);
                 var fields_buf: [3]*const llvm.Type = .{
-                    payload_llvm_ty, dg.context.intType(1), undefined,
+                    payload_llvm_ty, dg.context.intType(8), undefined,
                 };
                 const offset = child_ty.abiSize(target) + 1;
                 const abi_size = t.abiSize(target);
@@ -3134,12 +3134,13 @@ pub const DeclGen = struct {
                 else => unreachable,
             },
             .Optional => {
-                comptime assert(optional_layout_version == 2);
+                comptime assert(optional_layout_version == 3);
                 var buf: Type.Payload.ElemType = undefined;
                 const payload_ty = tv.ty.optionalChild(&buf);
-                const llvm_i1 = dg.context.intType(1);
+
+                const llvm_i8 = dg.context.intType(8);
                 const is_pl = !tv.val.isNull();
-                const non_null_bit = if (is_pl) llvm_i1.constAllOnes() else llvm_i1.constNull();
+                const non_null_bit = if (is_pl) llvm_i8.constInt(1, .False) else llvm_i8.constNull();
                 if (!payload_ty.hasRuntimeBitsIgnoreComptime()) {
                     return non_null_bit;
                 }
@@ -4041,10 +4042,10 @@ pub const FuncGen = struct {
                 .cmp_vector => try self.airCmpVector(inst),
                 .cmp_lt_errors_len => try self.airCmpLtErrorsLen(inst),
 
-                .is_non_null     => try self.airIsNonNull(inst, false, false, .NE),
-                .is_non_null_ptr => try self.airIsNonNull(inst, true , false, .NE),
-                .is_null         => try self.airIsNonNull(inst, false, true , .EQ),
-                .is_null_ptr     => try self.airIsNonNull(inst, true , true , .EQ),
+                .is_non_null     => try self.airIsNonNull(inst, false, .NE),
+                .is_non_null_ptr => try self.airIsNonNull(inst, true , .NE),
+                .is_null         => try self.airIsNonNull(inst, false, .EQ),
+                .is_null_ptr     => try self.airIsNonNull(inst, true , .EQ),
 
                 .is_non_err      => try self.airIsErr(inst, .EQ, false),
                 .is_non_err_ptr  => try self.airIsErr(inst, .EQ, true),
@@ -5633,7 +5634,6 @@ pub const FuncGen = struct {
         self: *FuncGen,
         inst: Air.Inst.Index,
         operand_is_ptr: bool,
-        invert: bool,
         pred: llvm.IntPredicate,
     ) !?*const llvm.Value {
         if (self.liveness.isUnused(inst)) return null;
@@ -5648,20 +5648,19 @@ pub const FuncGen = struct {
             return self.builder.buildICmp(pred, loaded, optional_llvm_ty.constNull(), "");
         }
 
+        comptime assert(optional_layout_version == 3);
+
         var buf: Type.Payload.ElemType = undefined;
         const payload_ty = optional_ty.optionalChild(&buf);
         if (!payload_ty.hasRuntimeBitsIgnoreComptime()) {
             const loaded = if (operand_is_ptr) self.builder.buildLoad(operand, "") else operand;
-            if (invert) {
-                return self.builder.buildNot(loaded, "");
-            } else {
-                return loaded;
-            }
+            const llvm_i8 = self.dg.context.intType(8);
+            return self.builder.buildICmp(pred, loaded, llvm_i8.constNull(), "");
         }
 
         const is_by_ref = operand_is_ptr or isByRef(optional_ty);
         const non_null_bit = self.optIsNonNull(operand, is_by_ref);
-        if (invert) {
+        if (pred == .EQ) {
             return self.builder.buildNot(non_null_bit, "");
         } else {
             return non_null_bit;
@@ -5740,15 +5739,17 @@ pub const FuncGen = struct {
     }
 
     fn airOptionalPayloadPtrSet(self: *FuncGen, inst: Air.Inst.Index) !?*const llvm.Value {
+        comptime assert(optional_layout_version == 3);
+
         const ty_op = self.air.instructions.items(.data)[inst].ty_op;
         const operand = try self.resolveInst(ty_op.operand);
         const optional_ty = self.air.typeOf(ty_op.operand).childType();
         const result_ty = self.air.getRefType(ty_op.ty);
         var buf: Type.Payload.ElemType = undefined;
         const payload_ty = optional_ty.optionalChild(&buf);
-        const non_null_bit = self.context.intType(1).constAllOnes();
+        const non_null_bit = self.context.intType(8).constInt(1, .False);
         if (!payload_ty.hasRuntimeBitsIgnoreComptime()) {
-            // We have a pointer to a i1. We need to set it to 1 and then return the same pointer.
+            // We have a pointer to a i8. We need to set it to 1 and then return the same pointer.
             _ = self.builder.buildStore(non_null_bit, operand);
 
             // TODO once we update to LLVM 14 this bitcast won't be necessary.
@@ -5914,8 +5915,8 @@ pub const FuncGen = struct {
 
         const ty_op = self.air.instructions.items(.data)[inst].ty_op;
         const payload_ty = self.air.typeOf(ty_op.operand);
-        const non_null_bit = self.context.intType(1).constAllOnes();
-        comptime assert(optional_layout_version == 2);
+        const non_null_bit = self.context.intType(8).constInt(1, .False);
+        comptime assert(optional_layout_version == 3);
         if (!payload_ty.hasRuntimeBitsIgnoreComptime()) return non_null_bit;
         const operand = try self.resolveInst(ty_op.operand);
         const optional_ty = self.air.typeOfIndex(inst);
@@ -7345,10 +7346,12 @@ pub const FuncGen = struct {
             return self.builder.buildSelect(success_bit, payload.typeOf().constNull(), payload, "");
         }
 
+        comptime assert(optional_layout_version == 3);
         const optional_llvm_ty = try self.dg.lowerType(optional_ty);
         const non_null_bit = self.builder.buildNot(success_bit, "");
+        const non_null_field = self.builder.buildZExt(non_null_bit, self.dg.context.intType(8), "");
         const partial = self.builder.buildInsertValue(optional_llvm_ty.getUndef(), payload, 0, "");
-        return self.builder.buildInsertValue(partial, non_null_bit, 1, "");
+        return self.builder.buildInsertValue(partial, non_null_field, 1, "");
     }
 
     fn airAtomicRmw(self: *FuncGen, inst: Air.Inst.Index) !?*const llvm.Value {
@@ -8331,19 +8334,24 @@ pub const FuncGen = struct {
 
     /// Assumes the optional is not pointer-like and payload has bits.
     fn optIsNonNull(self: *FuncGen, opt_handle: *const llvm.Value, is_by_ref: bool) *const llvm.Value {
-        if (is_by_ref) {
-            const index_type = self.context.intType(32);
+        const field = b: {
+            if (is_by_ref) {
+                const index_type = self.context.intType(32);
 
-            const indices: [2]*const llvm.Value = .{
-                index_type.constNull(),
-                index_type.constInt(1, .False),
-            };
+                const indices: [2]*const llvm.Value = .{
+                    index_type.constNull(),
+                    index_type.constInt(1, .False),
+                };
 
-            const field_ptr = self.builder.buildInBoundsGEP(opt_handle, &indices, indices.len, "");
-            return self.builder.buildLoad(field_ptr, "");
-        }
+                const field_ptr = self.builder.buildInBoundsGEP(opt_handle, &indices, indices.len, "");
+                break :b self.builder.buildLoad(field_ptr, "");
+            }
+
+            break :b self.builder.buildExtractValue(opt_handle, 1, "");
+        };
+        comptime assert(optional_layout_version == 3);
 
-        return self.builder.buildExtractValue(opt_handle, 1, "");
+        return self.builder.buildICmp(.NE, field, self.context.intType(8).constInt(0, .False), "");
     }
 
     /// Assumes the optional is not pointer-like and payload has bits.
@@ -9369,7 +9377,10 @@ fn intrinsicsAllowed(scalar_ty: Type, target: std.Target) bool {
 /// We can do this because for all types, Zig ABI alignment >= LLVM ABI
 /// alignment.
 const struct_layout_version = 2;
-const optional_layout_version = 2;
+
+// TODO: Restore the non_null field to i1 once
+//       https://github.com/llvm/llvm-project/issues/56585/ is fixed
+const optional_layout_version = 3;
 
 /// We use the least significant bit of the pointer address to tell us
 /// whether the type is fully resolved. Types that are only fwd declared