Merge branch 'assignment-result-loc'

With this merge, assignments participate in result location semantics.
2019-08-02 16:10:45 -04:00
parent 6cb4cac5cd d105769926
commit b2d94f9af2
7 changed files with 129 additions and 58 deletions
--- a/src/all_types.hpp
+++ b/src/all_types.hpp
@@ -2543,6 +2543,7 @@ struct IrInstructionLoadPtrGen {
 struct IrInstructionStorePtr {
    IrInstruction base;

+    bool allow_write_through_const;
    IrInstruction *ptr;
    IrInstruction *value;
 };
@@ -3707,6 +3708,7 @@ enum ResultLocId {
 struct ResultLoc {
    ResultLocId id;
    bool written;
+    bool allow_write_through_const;
    IrInstruction *resolved_loc; // result ptr 
    IrInstruction *source_instruction;
    IrInstruction *gen_instruction; // value to store to the result loc
--- a/src/codegen.cpp
+++ b/src/codegen.cpp
@@ -4458,8 +4458,14 @@ static LLVMValueRef ir_render_cmpxchg(CodeGen *g, IrExecutable *executable, IrIn
        return LLVMBuildSelect(g->builder, success_bit, LLVMConstNull(get_llvm_type(g, child_type)), payload_val, "");
    }

+    // When the cmpxchg is discarded, the result location will have no bits.
+    if (!type_has_bits(instruction->result_loc->value.type)) {
+        return nullptr;
+    }
+
    LLVMValueRef result_loc = ir_llvm_value(g, instruction->result_loc);
-    assert(type_has_bits(child_type));
+    src_assert(result_loc != nullptr, instruction->base.source_node);
+    src_assert(type_has_bits(child_type), instruction->base.source_node);

    LLVMValueRef payload_val = LLVMBuildExtractValue(g->builder, result_val, 0, "");
    LLVMValueRef val_ptr = LLVMBuildStructGEP(g->builder, result_loc, maybe_child_index, "");
--- a/src/ir.cpp
+++ b/src/ir.cpp
@@ -189,7 +189,8 @@ static IrInstruction *ir_analyze_bit_cast(IrAnalyze *ira, IrInstruction *source_
 static IrInstruction *ir_resolve_result_raw(IrAnalyze *ira, IrInstruction *suspend_source_instr,
        ResultLoc *result_loc, ZigType *value_type, IrInstruction *value, bool force_runtime, bool non_null_comptime);
 static IrInstruction *ir_resolve_result(IrAnalyze *ira, IrInstruction *suspend_source_instr,
-        ResultLoc *result_loc, ZigType *value_type, IrInstruction *value, bool force_runtime, bool non_null_comptime);
+        ResultLoc *result_loc, ZigType *value_type, IrInstruction *value, bool force_runtime,
+        bool non_null_comptime, bool allow_discard);
 static IrInstruction *ir_analyze_unwrap_optional_payload(IrAnalyze *ira, IrInstruction *source_instr,
        IrInstruction *base_ptr, bool safety_check_on, bool initializing);
 static IrInstruction *ir_analyze_unwrap_error_payload(IrAnalyze *ira, IrInstruction *source_instr,
@@ -197,7 +198,7 @@ static IrInstruction *ir_analyze_unwrap_error_payload(IrAnalyze *ira, IrInstruct
 static IrInstruction *ir_analyze_unwrap_err_code(IrAnalyze *ira, IrInstruction *source_instr,
        IrInstruction *base_ptr, bool initializing);
 static IrInstruction *ir_analyze_store_ptr(IrAnalyze *ira, IrInstruction *source_instr,
-        IrInstruction *ptr, IrInstruction *uncasted_value);
+        IrInstruction *ptr, IrInstruction *uncasted_value, bool allow_write_through_const);
 static IrInstruction *ir_gen_union_init_expr(IrBuilder *irb, Scope *scope, AstNode *source_node,
    IrInstruction *union_type, IrInstruction *field_name, AstNode *expr_node,
    LVal lval, ResultLoc *parent_result_loc);
@@ -1612,7 +1613,7 @@ static IrInstruction *ir_build_unreachable(IrBuilder *irb, Scope *scope, AstNode
    return &unreachable_instruction->base;
 }

-static IrInstruction *ir_build_store_ptr(IrBuilder *irb, Scope *scope, AstNode *source_node,
+static IrInstructionStorePtr *ir_build_store_ptr(IrBuilder *irb, Scope *scope, AstNode *source_node,
        IrInstruction *ptr, IrInstruction *value)
 {
    IrInstructionStorePtr *instruction = ir_build_instruction<IrInstructionStorePtr>(irb, scope, source_node);
@@ -1624,7 +1625,7 @@ static IrInstruction *ir_build_store_ptr(IrBuilder *irb, Scope *scope, AstNode *
    ir_ref_instruction(ptr, irb->current_basic_block);
    ir_ref_instruction(value, irb->current_basic_block);

-    return &instruction->base;
+    return instruction;
 }

 static IrInstruction *ir_build_var_decl_src(IrBuilder *irb, Scope *scope, AstNode *source_node,
@@ -4001,12 +4002,20 @@ static IrInstruction *ir_gen_bin_op_id(IrBuilder *irb, Scope *scope, AstNode *no

 static IrInstruction *ir_gen_assign(IrBuilder *irb, Scope *scope, AstNode *node) {
    IrInstruction *lvalue = ir_gen_node_extra(irb, node->data.bin_op_expr.op1, scope, LValPtr, nullptr);
-    IrInstruction *rvalue = ir_gen_node(irb, node->data.bin_op_expr.op2, scope);
-
-    if (lvalue == irb->codegen->invalid_instruction || rvalue == irb->codegen->invalid_instruction)
+    if (lvalue == irb->codegen->invalid_instruction)
+        return irb->codegen->invalid_instruction;
+
+    ResultLocInstruction *result_loc_inst = allocate<ResultLocInstruction>(1);
+    result_loc_inst->base.id = ResultLocIdInstruction;
+    result_loc_inst->base.source_instruction = lvalue;
+    ir_ref_instruction(lvalue, irb->current_basic_block);
+    ir_build_reset_result(irb, scope, node, &result_loc_inst->base);
+
+    IrInstruction *rvalue = ir_gen_node_extra(irb, node->data.bin_op_expr.op2, scope, LValNone,
+            &result_loc_inst->base);
+    if (rvalue == irb->codegen->invalid_instruction)
        return irb->codegen->invalid_instruction;

-    ir_build_store_ptr(irb, scope, node, lvalue, rvalue);
    return ir_build_const_void(irb, scope, node);
 }

@@ -6042,6 +6051,7 @@ static IrInstruction *ir_gen_container_init_expr(IrBuilder *irb, Scope *scope, A
                ResultLocInstruction *result_loc_inst = allocate<ResultLocInstruction>(1);
                result_loc_inst->base.id = ResultLocIdInstruction;
                result_loc_inst->base.source_instruction = field_ptr;
+                result_loc_inst->base.allow_write_through_const = true;
                ir_ref_instruction(field_ptr, irb->current_basic_block);
                ir_build_reset_result(irb, scope, expr_node, &result_loc_inst->base);

@@ -6080,6 +6090,7 @@ static IrInstruction *ir_gen_container_init_expr(IrBuilder *irb, Scope *scope, A
                ResultLocInstruction *result_loc_inst = allocate<ResultLocInstruction>(1);
                result_loc_inst->base.id = ResultLocIdInstruction;
                result_loc_inst->base.source_instruction = elem_ptr;
+                result_loc_inst->base.allow_write_through_const = true;
                ir_ref_instruction(elem_ptr, irb->current_basic_block);
                ir_build_reset_result(irb, scope, expr_node, &result_loc_inst->base);

@@ -6637,7 +6648,7 @@ static IrInstruction *ir_gen_for_expr(IrBuilder *irb, Scope *parent_scope, AstNo

    ir_set_cursor_at_end_and_append_block(irb, continue_block);
    IrInstruction *new_index_val = ir_build_bin_op(irb, child_scope, node, IrBinOpAdd, index_val, one, false);
-    ir_mark_gen(ir_build_store_ptr(irb, child_scope, node, index_ptr, new_index_val));
+    ir_build_store_ptr(irb, child_scope, node, index_ptr, new_index_val)->allow_write_through_const = true;
    ir_build_br(irb, child_scope, node, cond_block, is_comptime);

    IrInstruction *else_result = nullptr;
@@ -11155,7 +11166,8 @@ static IrInstruction *ir_resolve_ptr_of_array_to_slice(IrAnalyze *ira, IrInstruc
    }

    if (result_loc == nullptr) result_loc = no_result_loc();
-    IrInstruction *result_loc_inst = ir_resolve_result(ira, source_instr, result_loc, wanted_type, nullptr, true, false);
+    IrInstruction *result_loc_inst = ir_resolve_result(ira, source_instr, result_loc, wanted_type, nullptr, true,
+            false, true);
    if (type_is_invalid(result_loc_inst->value.type) || instr_is_unreachable(result_loc_inst)) {
        return result_loc_inst;
    }
@@ -11615,7 +11627,7 @@ static IrInstruction *ir_analyze_optional_wrap(IrAnalyze *ira, IrInstruction *so
    }
    IrInstruction *result_loc_inst = nullptr;
    if (result_loc != nullptr) {
-        result_loc_inst = ir_resolve_result(ira, source_instr, result_loc, wanted_type, nullptr, true, false);
+        result_loc_inst = ir_resolve_result(ira, source_instr, result_loc, wanted_type, nullptr, true, false, true);
        if (type_is_invalid(result_loc_inst->value.type) || instr_is_unreachable(result_loc_inst)) {
            return result_loc_inst;
        }
@@ -11658,7 +11670,7 @@ static IrInstruction *ir_analyze_err_wrap_payload(IrAnalyze *ira, IrInstruction
    IrInstruction *result_loc_inst;
    if (handle_is_ptr(wanted_type)) {
        if (result_loc == nullptr) result_loc = no_result_loc();
-        result_loc_inst = ir_resolve_result(ira, source_instr, result_loc, wanted_type, nullptr, true, false);
+        result_loc_inst = ir_resolve_result(ira, source_instr, result_loc, wanted_type, nullptr, true, false, true);
        if (type_is_invalid(result_loc_inst->value.type) || instr_is_unreachable(result_loc_inst)) {
            return result_loc_inst;
        }
@@ -11743,7 +11755,7 @@ static IrInstruction *ir_analyze_err_wrap_code(IrAnalyze *ira, IrInstruction *so
    IrInstruction *result_loc_inst;
    if (handle_is_ptr(wanted_type)) {
        if (result_loc == nullptr) result_loc = no_result_loc();
-        result_loc_inst = ir_resolve_result(ira, source_instr, result_loc, wanted_type, nullptr, true, false);
+        result_loc_inst = ir_resolve_result(ira, source_instr, result_loc, wanted_type, nullptr, true, false, true);
        if (type_is_invalid(result_loc_inst->value.type) || instr_is_unreachable(result_loc_inst)) {
            return result_loc_inst;
        }
@@ -11816,7 +11828,8 @@ static IrInstruction *ir_get_ref(IrAnalyze *ira, IrInstruction *source_instructi

    IrInstruction *result_loc;
    if (type_has_bits(ptr_type) && !handle_is_ptr(value->value.type)) {
-        result_loc = ir_resolve_result(ira, source_instruction, no_result_loc(), value->value.type, nullptr, true, false);
+        result_loc = ir_resolve_result(ira, source_instruction, no_result_loc(), value->value.type, nullptr, true,
+                false, true);
    } else {
        result_loc = nullptr;
    }
@@ -11860,7 +11873,8 @@ static IrInstruction *ir_analyze_array_to_slice(IrAnalyze *ira, IrInstruction *s
    if (!array_ptr) array_ptr = ir_get_ref(ira, source_instr, array, true, false);

    if (result_loc == nullptr) result_loc = no_result_loc();
-    IrInstruction *result_loc_inst = ir_resolve_result(ira, source_instr, result_loc, wanted_type, nullptr, true, false);
+    IrInstruction *result_loc_inst = ir_resolve_result(ira, source_instr, result_loc, wanted_type, nullptr,
+            true, false, true);
    if (type_is_invalid(result_loc_inst->value.type) || instr_is_unreachable(result_loc_inst)) {
        return result_loc_inst;
    }
@@ -12516,7 +12530,8 @@ static IrInstruction *ir_analyze_vector_to_array(IrAnalyze *ira, IrInstruction *
    if (result_loc == nullptr) {
        result_loc = no_result_loc();
    }
-    IrInstruction *result_loc_inst = ir_resolve_result(ira, source_instr, result_loc, array_type, nullptr, true, false);
+    IrInstruction *result_loc_inst = ir_resolve_result(ira, source_instr, result_loc, array_type, nullptr,
+            true, false, true);
    if (type_is_invalid(result_loc_inst->value.type) || instr_is_unreachable(result_loc_inst)) {
        return result_loc_inst;
    }
@@ -13097,7 +13112,8 @@ static IrInstruction *ir_get_deref(IrAnalyze *ira, IrInstruction *source_instruc
    IrInstruction *result_loc_inst;
    if (type_entry->data.pointer.host_int_bytes != 0 && handle_is_ptr(child_type)) {
        if (result_loc == nullptr) result_loc = no_result_loc();
-        result_loc_inst = ir_resolve_result(ira, source_instruction, result_loc, child_type, nullptr, true, false);
+        result_loc_inst = ir_resolve_result(ira, source_instruction, result_loc, child_type, nullptr,
+                true, false, true);
        if (type_is_invalid(result_loc_inst->value.type) || instr_is_unreachable(result_loc_inst)) {
            return result_loc_inst;
        }
@@ -14834,7 +14850,7 @@ static IrInstruction *ir_analyze_instruction_decl_var(IrAnalyze *ira,
            // instruction.
            assert(deref->value.special != ConstValSpecialRuntime);
            var_ptr->value.special = ConstValSpecialRuntime;
-            ir_analyze_store_ptr(ira, var_ptr, var_ptr, deref);
+            ir_analyze_store_ptr(ira, var_ptr, var_ptr, deref, false);
        }

        if (var_ptr->value.special == ConstValSpecialStatic && var->mem_slot_index != SIZE_MAX) {
@@ -15352,7 +15368,7 @@ static IrInstruction *ir_resolve_result_raw(IrAnalyze *ira, IrInstruction *suspe

            if (peer_parent->peers.length == 1) {
                IrInstruction *parent_result_loc = ir_resolve_result(ira, suspend_source_instr, peer_parent->parent,
-                        value_type, value, force_runtime, non_null_comptime);
+                        value_type, value, force_runtime, non_null_comptime, true);
                result_peer->suspend_pos.basic_block_index = SIZE_MAX;
                result_peer->suspend_pos.instruction_index = SIZE_MAX;
                if (parent_result_loc == nullptr || type_is_invalid(parent_result_loc->value.type) ||
@@ -15372,7 +15388,7 @@ static IrInstruction *ir_resolve_result_raw(IrAnalyze *ira, IrInstruction *suspe
            if (peer_parent->skipped) {
                if (non_null_comptime) {
                    return ir_resolve_result(ira, suspend_source_instr, peer_parent->parent,
-                            value_type, value, force_runtime, non_null_comptime);
+                            value_type, value, force_runtime, non_null_comptime, true);
                }
                return nullptr;
            }
@@ -15390,7 +15406,7 @@ static IrInstruction *ir_resolve_result_raw(IrAnalyze *ira, IrInstruction *suspe
            }

            IrInstruction *parent_result_loc = ir_resolve_result(ira, suspend_source_instr, peer_parent->parent,
-                    peer_parent->resolved_type, nullptr, force_runtime, non_null_comptime);
+                    peer_parent->resolved_type, nullptr, force_runtime, non_null_comptime, true);
            if (parent_result_loc == nullptr || type_is_invalid(parent_result_loc->value.type) ||
                parent_result_loc->value.type->id == ZigTypeIdUnreachable)
            {
@@ -15440,7 +15456,7 @@ static IrInstruction *ir_resolve_result_raw(IrAnalyze *ira, IrInstruction *suspe
            }

            IrInstruction *parent_result_loc = ir_resolve_result(ira, suspend_source_instr, result_bit_cast->parent,
-                    dest_type, bitcasted_value, force_runtime, non_null_comptime);
+                    dest_type, bitcasted_value, force_runtime, non_null_comptime, true);
            if (parent_result_loc == nullptr || type_is_invalid(parent_result_loc->value.type) ||
                parent_result_loc->value.type->id == ZigTypeIdUnreachable)
            {
@@ -15469,8 +15485,15 @@ static IrInstruction *ir_resolve_result_raw(IrAnalyze *ira, IrInstruction *suspe

 static IrInstruction *ir_resolve_result(IrAnalyze *ira, IrInstruction *suspend_source_instr,
        ResultLoc *result_loc_pass1, ZigType *value_type, IrInstruction *value, bool force_runtime,
-        bool non_null_comptime)
+        bool non_null_comptime, bool allow_discard)
 {
+    if (!allow_discard && result_loc_pass1->id == ResultLocIdInstruction &&
+        instr_is_comptime(result_loc_pass1->source_instruction) &&
+        result_loc_pass1->source_instruction->value.type->id == ZigTypeIdPointer &&
+        result_loc_pass1->source_instruction->value.data.x_ptr.special == ConstPtrSpecialDiscard)
+    {
+        result_loc_pass1 = no_result_loc();
+    }
    IrInstruction *result_loc = ir_resolve_result_raw(ira, suspend_source_instr, result_loc_pass1, value_type,
            value, force_runtime, non_null_comptime);
    if (result_loc == nullptr || (instr_is_unreachable(result_loc) || type_is_invalid(result_loc->value.type)))
@@ -15525,7 +15548,7 @@ static IrInstruction *ir_analyze_instruction_resolve_result(IrAnalyze *ira, IrIn
    if (type_is_invalid(implicit_elem_type))
        return ira->codegen->invalid_instruction;
    IrInstruction *result_loc = ir_resolve_result(ira, &instruction->base, instruction->result_loc,
-            implicit_elem_type, nullptr, false, true);
+            implicit_elem_type, nullptr, false, true, true);
    if (result_loc != nullptr)
        return result_loc;

@@ -15534,7 +15557,7 @@ static IrInstruction *ir_analyze_instruction_resolve_result(IrAnalyze *ira, IrIn
            instruction->result_loc->id == ResultLocIdReturn)
    {
        result_loc = ir_resolve_result(ira, &instruction->base, no_result_loc(),
-                implicit_elem_type, nullptr, false, true);
+                implicit_elem_type, nullptr, false, true, true);
        if (result_loc != nullptr &&
                (type_is_invalid(result_loc->value.type) || instr_is_unreachable(result_loc)))
        {
@@ -15623,7 +15646,7 @@ static IrInstruction *ir_analyze_async_call(IrAnalyze *ira, IrInstructionCallSrc
    ZigType *async_return_type = get_error_union_type(ira->codegen, alloc_fn_error_set_type, promise_type);

    IrInstruction *result_loc = ir_resolve_result(ira, &call_instruction->base, no_result_loc(),
-            async_return_type, nullptr, true, true);
+            async_return_type, nullptr, true, true, false);
    if (type_is_invalid(result_loc->value.type) || instr_is_unreachable(result_loc)) {
        return result_loc;
    }
@@ -15841,7 +15864,7 @@ no_mem_slot:
 }

 static IrInstruction *ir_analyze_store_ptr(IrAnalyze *ira, IrInstruction *source_instr,
-        IrInstruction *ptr, IrInstruction *uncasted_value)
+        IrInstruction *ptr, IrInstruction *uncasted_value, bool allow_write_through_const)
 {
    assert(ptr->value.type->id == ZigTypeIdPointer);

@@ -15857,7 +15880,7 @@ static IrInstruction *ir_analyze_store_ptr(IrAnalyze *ira, IrInstruction *source

    ZigType *child_type = ptr->value.type->data.pointer.child_type;

-    if (ptr->value.type->data.pointer.is_const && !source_instr->is_gen) {
+    if (ptr->value.type->data.pointer.is_const && !allow_write_through_const) {
        ir_add_error(ira, source_instr, buf_sprintf("cannot assign to constant"));
        return ira->codegen->invalid_instruction;
    }
@@ -15936,10 +15959,9 @@ static IrInstruction *ir_analyze_store_ptr(IrAnalyze *ira, IrInstruction *source
            break;
    }

-    IrInstruction *result = ir_build_store_ptr(&ira->new_irb, source_instr->scope, source_instr->source_node,
-        ptr, value);
-    result->value.type = ira->codegen->builtin_types.entry_void;
-    return result;
+    IrInstructionStorePtr *store_ptr = ir_build_store_ptr(&ira->new_irb, source_instr->scope,
+            source_instr->source_node, ptr, value);
+    return &store_ptr->base;
 }

 static IrInstruction *ir_analyze_fn_call(IrAnalyze *ira, IrInstructionCallSrc *call_instruction,
@@ -16382,7 +16404,7 @@ static IrInstruction *ir_analyze_fn_call(IrAnalyze *ira, IrInstructionCallSrc *c
        IrInstruction *result_loc;
        if (handle_is_ptr(impl_fn_type_id->return_type)) {
            result_loc = ir_resolve_result(ira, &call_instruction->base, call_instruction->result_loc,
-                    impl_fn_type_id->return_type, nullptr, true, true);
+                    impl_fn_type_id->return_type, nullptr, true, true, false);
            if (result_loc != nullptr && (type_is_invalid(result_loc->value.type) ||
                        instr_is_unreachable(result_loc)))
            {
@@ -16504,7 +16526,7 @@ static IrInstruction *ir_analyze_fn_call(IrAnalyze *ira, IrInstructionCallSrc *c
    IrInstruction *result_loc;
    if (handle_is_ptr(return_type)) {
        result_loc = ir_resolve_result(ira, &call_instruction->base, call_instruction->result_loc,
-                return_type, nullptr, true, true);
+                return_type, nullptr, true, true, false);
        if (result_loc != nullptr && (type_is_invalid(result_loc->value.type) || instr_is_unreachable(result_loc))) {
            return result_loc;
        }
@@ -17020,7 +17042,7 @@ static IrInstruction *ir_analyze_instruction_phi(IrAnalyze *ira, IrInstructionPh

            // In case resolving the parent activates a suspend, do it now
            IrInstruction *parent_result_loc = ir_resolve_result(ira, &phi_instruction->base, peer_parent->parent,
-                    peer_parent->resolved_type, nullptr, false, false);
+                    peer_parent->resolved_type, nullptr, false, false, true);
            if (parent_result_loc != nullptr &&
                (type_is_invalid(parent_result_loc->value.type) || instr_is_unreachable(parent_result_loc)))
            {
@@ -17477,6 +17499,7 @@ static IrInstruction *ir_analyze_instruction_elem_ptr(IrAnalyze *ira, IrInstruct
                    return result;
                } else if (is_slice(array_type)) {
                    ConstExprValue *ptr_field = &array_ptr_val->data.x_struct.fields[slice_ptr_index];
+                    ir_assert(ptr_field != nullptr, &elem_ptr_instruction->base);
                    if (ptr_field->data.x_ptr.special == ConstPtrSpecialHardCodedAddr) {
                        IrInstruction *result = ir_build_elem_ptr(&ira->new_irb, elem_ptr_instruction->base.scope,
                                elem_ptr_instruction->base.source_node, array_ptr, casted_elem_index, false,
@@ -17663,7 +17686,7 @@ static IrInstruction *ir_analyze_struct_field_ptr(IrAnalyze *ira, IrInstruction
                return ira->codegen->invalid_instruction;
            if (type_is_invalid(struct_val->type))
                return ira->codegen->invalid_instruction;
-            if (struct_val->special == ConstValSpecialUndef && initializing) {
+            if (initializing && struct_val->special == ConstValSpecialUndef) {
                struct_val->data.x_struct.fields = create_const_vals(struct_type->data.structure.src_field_count);
                struct_val->special = ConstValSpecialStatic;
                for (size_t i = 0; i < struct_type->data.structure.src_field_count; i += 1) {
@@ -18261,7 +18284,7 @@ static IrInstruction *ir_analyze_instruction_store_ptr(IrAnalyze *ira, IrInstruc
    if (type_is_invalid(value->value.type))
        return ira->codegen->invalid_instruction;

-    return ir_analyze_store_ptr(ira, &instruction->base, ptr, value);
+    return ir_analyze_store_ptr(ira, &instruction->base, ptr, value, instruction->allow_write_through_const);
 }

 static IrInstruction *ir_analyze_instruction_load_ptr(IrAnalyze *ira, IrInstructionLoadPtr *instruction) {
@@ -18764,7 +18787,7 @@ static IrInstruction *ir_analyze_unwrap_optional_payload(IrAnalyze *ira, IrInstr
            if (optional_val == nullptr)
                return ira->codegen->invalid_instruction;

-            if (initializing && optional_val->special == ConstValSpecialUndef) {
+            if (initializing) {
                switch (type_has_one_possible_value(ira->codegen, child_type)) {
                    case OnePossibleValueInvalid:
                        return ira->codegen->invalid_instruction;
@@ -19669,7 +19692,7 @@ static IrInstruction *ir_analyze_container_init_fields(IrAnalyze *ira, IrInstruc

        IrInstruction *field_ptr = ir_analyze_struct_field_ptr(ira, instruction, field, result_loc,
                container_type, true);
-        ir_analyze_store_ptr(ira, instruction, field_ptr, runtime_inst);
+        ir_analyze_store_ptr(ira, instruction, field_ptr, runtime_inst, false);
        if (instr_is_comptime(field_ptr) && field_ptr->value.data.x_ptr.mut != ConstPtrMutRuntimeVar) {
            const_ptrs.append(field_ptr);
        } else {
@@ -19686,7 +19709,7 @@ static IrInstruction *ir_analyze_container_init_fields(IrAnalyze *ira, IrInstruc
                IrInstruction *field_result_loc = const_ptrs.at(i);
                IrInstruction *deref = ir_get_deref(ira, field_result_loc, field_result_loc, nullptr);
                field_result_loc->value.special = ConstValSpecialRuntime;
-                ir_analyze_store_ptr(ira, field_result_loc, field_result_loc, deref);
+                ir_analyze_store_ptr(ira, field_result_loc, field_result_loc, deref, false);
            }
        }
    }
@@ -19813,7 +19836,7 @@ static IrInstruction *ir_analyze_instruction_container_init_list(IrAnalyze *ira,
                assert(elem_result_loc->value.special == ConstValSpecialStatic);
                IrInstruction *deref = ir_get_deref(ira, elem_result_loc, elem_result_loc, nullptr);
                elem_result_loc->value.special = ConstValSpecialRuntime;
-                ir_analyze_store_ptr(ira, elem_result_loc, elem_result_loc, deref);
+                ir_analyze_store_ptr(ira, elem_result_loc, elem_result_loc, deref, false);
            }
        }
    }
@@ -21532,7 +21555,7 @@ static IrInstruction *ir_analyze_instruction_cmpxchg(IrAnalyze *ira, IrInstructi
    IrInstruction *result_loc;
    if (handle_is_ptr(result_type)) {
        result_loc = ir_resolve_result(ira, &instruction->base, instruction->result_loc,
-                result_type, nullptr, true, false);
+                result_type, nullptr, true, false, true);
        if (type_is_invalid(result_loc->value.type) || instr_is_unreachable(result_loc)) {
            return result_loc;
        }
@@ -21789,7 +21812,7 @@ static IrInstruction *ir_analyze_instruction_from_bytes(IrAnalyze *ira, IrInstru
    }

    IrInstruction *result_loc = ir_resolve_result(ira, &instruction->base, instruction->result_loc,
-            dest_slice_type, nullptr, true, false);
+            dest_slice_type, nullptr, true, false, true);
    if (result_loc != nullptr && (type_is_invalid(result_loc->value.type) || instr_is_unreachable(result_loc))) {
        return result_loc;
    }
@@ -21866,7 +21889,7 @@ static IrInstruction *ir_analyze_instruction_to_bytes(IrAnalyze *ira, IrInstruct
    }

    IrInstruction *result_loc = ir_resolve_result(ira, &instruction->base, instruction->result_loc,
-            dest_slice_type, nullptr, true, false);
+            dest_slice_type, nullptr, true, false, true);
    if (type_is_invalid(result_loc->value.type) || instr_is_unreachable(result_loc)) {
        return result_loc;
    }
@@ -22608,7 +22631,7 @@ static IrInstruction *ir_analyze_instruction_slice(IrAnalyze *ira, IrInstruction
    }

    IrInstruction *result_loc = ir_resolve_result(ira, &instruction->base, instruction->result_loc,
-            return_type, nullptr, true, false);
+            return_type, nullptr, true, false, true);
    if (type_is_invalid(result_loc->value.type) || instr_is_unreachable(result_loc)) {
        return result_loc;
    }
@@ -23260,7 +23283,7 @@ static IrInstruction *ir_analyze_unwrap_error_payload(IrAnalyze *ira, IrInstruct
            ConstExprValue *err_union_val = const_ptr_pointee(ira, ira->codegen, ptr_val, source_instr->source_node);
            if (err_union_val == nullptr)
                return ira->codegen->invalid_instruction;
-            if (err_union_val->special == ConstValSpecialUndef && initializing) {
+            if (initializing && err_union_val->special == ConstValSpecialUndef) {
                ConstExprValue *vals = create_const_vals(2);
                ConstExprValue *err_set_val = &vals[0];
                ConstExprValue *payload_val = &vals[1];
@@ -25388,7 +25411,7 @@ static IrInstruction *ir_analyze_instruction_end_expr(IrAnalyze *ira, IrInstruct

    bool was_written = instruction->result_loc->written;
    IrInstruction *result_loc = ir_resolve_result(ira, &instruction->base, instruction->result_loc,
-            value->value.type, value, false, false);
+            value->value.type, value, false, false, true);
    if (result_loc != nullptr) {
        if (type_is_invalid(result_loc->value.type))
            return ira->codegen->invalid_instruction;
@@ -25396,7 +25419,8 @@ static IrInstruction *ir_analyze_instruction_end_expr(IrAnalyze *ira, IrInstruct
            return result_loc;

        if (!was_written) {
-            IrInstruction *store_ptr = ir_analyze_store_ptr(ira, &instruction->base, result_loc, value);
+            IrInstruction *store_ptr = ir_analyze_store_ptr(ira, &instruction->base, result_loc, value,
+                    instruction->result_loc->allow_write_through_const);
            if (type_is_invalid(store_ptr->value.type)) {
                return ira->codegen->invalid_instruction;
            }
@@ -25420,7 +25444,7 @@ static IrInstruction *ir_analyze_instruction_bit_cast_src(IrAnalyze *ira, IrInst
        return operand;

    IrInstruction *result_loc = ir_resolve_result(ira, &instruction->base,
-            &instruction->result_loc_bit_cast->base, operand->value.type, operand, false, false);
+            &instruction->result_loc_bit_cast->base, operand->value.type, operand, false, false, true);
    if (result_loc != nullptr && (type_is_invalid(result_loc->value.type) || instr_is_unreachable(result_loc)))
        return result_loc;

--- a/test/compile_errors.zig
+++ b/test/compile_errors.zig
@@ -201,7 +201,7 @@ pub fn addCases(cases: *tests.CompileErrorContext) void {
        \\    return error.OutOfMemory;
        \\}
    ,
-        "tmp.zig:2:7: error: error is discarded",
+        "tmp.zig:2:12: error: error is discarded",
    );

    cases.add(
@@ -2740,7 +2740,7 @@ pub fn addCases(cases: *tests.CompileErrorContext) void {
        \\    3 = 3;
        \\}
    ,
-        "tmp.zig:2:7: error: cannot assign to constant",
+        "tmp.zig:2:9: error: cannot assign to constant",
    );

    cases.add(
@@ -2750,7 +2750,7 @@ pub fn addCases(cases: *tests.CompileErrorContext) void {
        \\    a = 4;
        \\}
    ,
-        "tmp.zig:3:7: error: cannot assign to constant",
+        "tmp.zig:3:9: error: cannot assign to constant",
    );

    cases.add(
@@ -2820,7 +2820,7 @@ pub fn addCases(cases: *tests.CompileErrorContext) void {
        \\}
        \\export fn entry() void { f(); }
    ,
-        "tmp.zig:3:7: error: cannot assign to constant",
+        "tmp.zig:3:9: error: cannot assign to constant",
    );

    cases.add(
@@ -3883,7 +3883,7 @@ pub fn addCases(cases: *tests.CompileErrorContext) void {
        \\
        \\export fn entry() usize { return @sizeOf(@typeOf(a)); }
    ,
-        "tmp.zig:6:24: error: unable to evaluate constant expression",
+        "tmp.zig:6:26: error: unable to evaluate constant expression",
        "tmp.zig:4:17: note: called from here",
    );

@@ -4133,7 +4133,7 @@ pub fn addCases(cases: *tests.CompileErrorContext) void {
        \\  cstr[0] = 'W';
        \\}
    ,
-        "tmp.zig:3:11: error: cannot assign to constant",
+        "tmp.zig:3:13: error: cannot assign to constant",
    );

    cases.add(
@@ -4143,7 +4143,7 @@ pub fn addCases(cases: *tests.CompileErrorContext) void {
        \\  cstr[0] = 'W';
        \\}
    ,
-        "tmp.zig:3:11: error: cannot assign to constant",
+        "tmp.zig:3:13: error: cannot assign to constant",
    );

    cases.add(
@@ -4291,7 +4291,7 @@ pub fn addCases(cases: *tests.CompileErrorContext) void {
        \\    f.field = 0;
        \\}
    ,
-        "tmp.zig:6:13: error: cannot assign to constant",
+        "tmp.zig:6:15: error: cannot assign to constant",
    );

    cases.add(
--- a/test/stage1/behavior/atomics.zig
+++ b/test/stage1/behavior/atomics.zig
@@ -1,5 +1,6 @@
 const std = @import("std");
 const expect = std.testing.expect;
+const expectEqual = std.testing.expectEqual;
 const builtin = @import("builtin");
 const AtomicRmwOp = builtin.AtomicRmwOp;
 const AtomicOrder = builtin.AtomicOrder;
@@ -90,3 +91,12 @@ test "cmpxchg with ptr" {
 //    expect(@cmpxchgStrong(u128, &x, 5678, 42, .SeqCst, .SeqCst) == null);
 //    expect(x == 42);
 //}
+
+test "cmpxchg with ignored result" {
+    var x: i32 = 1234;
+    var ptr = &x;
+
+    _ = @cmpxchgStrong(i32, &x, 1234, 5678, .Monotonic, .Monotonic);
+
+    expectEqual(i32(5678), x);
+}
--- a/test/stage1/behavior/eval.zig
+++ b/test/stage1/behavior/eval.zig
@@ -1,5 +1,6 @@
 const std = @import("std");
 const expect = std.testing.expect;
+const expectEqual = std.testing.expectEqual;
 const builtin = @import("builtin");

 test "compile time recursion" {
@@ -794,3 +795,12 @@ test "no undeclared identifier error in unanalyzed branches" {
        lol_this_doesnt_exist = nonsense;
    }
 }
+
+test "comptime assign int to optional int" {
+    comptime {
+        var x: ?i32 = null;
+        x = 2;
+        x.? *= 10;
+        expectEqual(20, x.?);
+    }
+}
--- a/test/stage1/behavior/fn.zig
+++ b/test/stage1/behavior/fn.zig
@@ -228,3 +228,22 @@ test "implicit cast fn call result to optional in field result" {
    S.entry();
    comptime S.entry();
 }
+
+test "discard the result of a function that returns a struct" {
+    const S = struct {
+        fn entry() void {
+            _ = func();
+        }
+
+        fn func() Foo {
+            return undefined;
+        }
+
+        const Foo = struct {
+            a: u64,
+            b: u64,
+        };
+    };
+    S.entry();
+    comptime S.entry();
+}