add implicit casts from *[N]T

* to `[]T`
 * to `[*]T`

See #770

src/all_types.hpp

@@ -583,6 +583,7 @@ enum CastOp {
     CastOpNumLitToConcrete,
     CastOpErrSet,
     CastOpBitCast,
+    CastOpPtrOfArrayToSlice,
 };
 
 struct AstNodeFnCallExpr {

src/codegen.cpp

@@ -2530,7 +2530,7 @@ static LLVMValueRef ir_render_cast(CodeGen *g, IrExecutable *executable,
                 assert(wanted_type->data.structure.is_slice);
                 assert(actual_type->id == TypeTableEntryIdArray);
 
-                TypeTableEntry *wanted_pointer_type = wanted_type->data.structure.fields[0].type_entry;
+                TypeTableEntry *wanted_pointer_type = wanted_type->data.structure.fields[slice_ptr_index].type_entry;
                 TypeTableEntry *wanted_child_type = wanted_pointer_type->data.pointer.child_type;
 
 
@@ -2576,6 +2576,29 @@ static LLVMValueRef ir_render_cast(CodeGen *g, IrExecutable *executable,
             return expr_val;
         case CastOpBitCast:
             return LLVMBuildBitCast(g->builder, expr_val, wanted_type->type_ref, "");
+        case CastOpPtrOfArrayToSlice: {
+            assert(cast_instruction->tmp_ptr);
+            assert(actual_type->id == TypeTableEntryIdPointer);
+            TypeTableEntry *array_type = actual_type->data.pointer.child_type;
+            assert(array_type->id == TypeTableEntryIdArray);
+
+            LLVMValueRef ptr_field_ptr = LLVMBuildStructGEP(g->builder, cast_instruction->tmp_ptr,
+                    slice_ptr_index, "");
+            LLVMValueRef indices[] = {
+                LLVMConstNull(g->builtin_types.entry_usize->type_ref),
+                LLVMConstInt(g->builtin_types.entry_usize->type_ref, 0, false),
+            };
+            LLVMValueRef slice_start_ptr = LLVMBuildInBoundsGEP(g->builder, expr_val, indices, 2, "");
+            gen_store_untyped(g, slice_start_ptr, ptr_field_ptr, 0, false);
+
+            LLVMValueRef len_field_ptr = LLVMBuildStructGEP(g->builder, cast_instruction->tmp_ptr,
+                    slice_len_index, "");
+            LLVMValueRef len_value = LLVMConstInt(g->builtin_types.entry_usize->type_ref,
+                    array_type->data.array.len, false);
+            gen_store_untyped(g, len_value, len_field_ptr, 0, false);
+
+            return cast_instruction->tmp_ptr;
+        }
     }
     zig_unreachable();
 }
@@ -3815,7 +3838,6 @@ static LLVMValueRef ir_render_slice(CodeGen *g, IrExecutable *executable, IrInst
         } else {
             end_val = LLVMConstInt(g->builtin_types.entry_usize->type_ref, array_type->data.array.len, false);
         }
-
         if (want_runtime_safety) {
             add_bounds_check(g, start_val, LLVMIntEQ, nullptr, LLVMIntULE, end_val);
             if (instruction->end) {

src/ir.cpp

@@ -108,6 +108,7 @@ static IrInstruction *ir_get_var_ptr(IrAnalyze *ira, IrInstruction *instruction,
 static TypeTableEntry *ir_resolve_atomic_operand_type(IrAnalyze *ira, IrInstruction *op);
 static IrInstruction *ir_lval_wrap(IrBuilder *irb, Scope *scope, IrInstruction *value, LVal lval);
 static TypeTableEntry *adjust_ptr_align(CodeGen *g, TypeTableEntry *ptr_type, uint32_t new_align);
+static TypeTableEntry *adjust_slice_align(CodeGen *g, TypeTableEntry *slice_type, uint32_t new_align);
 
 ConstExprValue *const_ptr_pointee(CodeGen *g, ConstExprValue *const_val) {
     assert(const_val->type->id == TypeTableEntryIdPointer);
@@ -8024,6 +8025,33 @@ static ImplicitCastMatchResult ir_types_match_with_implicit_cast(IrAnalyze *ira,
         }
     }
 
+    // implicit *[N]T to [*]T
+    if (expected_type->id == TypeTableEntryIdPointer &&
+        expected_type->data.pointer.ptr_len == PtrLenUnknown &&
+        actual_type->id == TypeTableEntryIdPointer &&
+        actual_type->data.pointer.ptr_len == PtrLenSingle &&
+        actual_type->data.pointer.child_type->id == TypeTableEntryIdArray &&
+        types_match_const_cast_only(ira, expected_type->data.pointer.child_type,
+            actual_type->data.pointer.child_type->data.array.child_type, source_node).id == ConstCastResultIdOk)
+    {
+        return ImplicitCastMatchResultYes;
+    }
+
+    // implicit *[N]T to []T
+    if (is_slice(expected_type) &&
+        actual_type->id == TypeTableEntryIdPointer &&
+        actual_type->data.pointer.ptr_len == PtrLenSingle &&
+        actual_type->data.pointer.child_type->id == TypeTableEntryIdArray)
+    {
+        TypeTableEntry *slice_ptr_type = expected_type->data.structure.fields[slice_ptr_index].type_entry;
+        assert(slice_ptr_type->id == TypeTableEntryIdPointer);
+        if (types_match_const_cast_only(ira, slice_ptr_type->data.pointer.child_type,
+            actual_type->data.pointer.child_type->data.array.child_type, source_node).id == ConstCastResultIdOk)
+        {
+            return ImplicitCastMatchResultYes;
+        }
+    }
+
     // implicit [N]T to ?[]const T
     if (expected_type->id == TypeTableEntryIdMaybe &&
         is_slice(expected_type->data.maybe.child_type) &&
@@ -8699,6 +8727,7 @@ static void eval_const_expr_implicit_cast(CastOp cast_op,
             zig_unreachable();
         case CastOpErrSet:
         case CastOpBitCast:
+        case CastOpPtrOfArrayToSlice:
             zig_panic("TODO");
         case CastOpNoop:
             {
@@ -8786,6 +8815,63 @@ static IrInstruction *ir_resolve_cast(IrAnalyze *ira, IrInstruction *source_inst
     }
 }
 
+static IrInstruction *ir_resolve_ptr_of_array_to_unknown_len_ptr(IrAnalyze *ira, IrInstruction *source_instr,
+        IrInstruction *value, TypeTableEntry *wanted_type)
+{
+    assert(value->value.type->id == TypeTableEntryIdPointer);
+    wanted_type = adjust_ptr_align(ira->codegen, wanted_type, value->value.type->data.pointer.alignment);
+
+    if (instr_is_comptime(value)) {
+        ConstExprValue *pointee = const_ptr_pointee(ira->codegen, &value->value);
+        if (pointee->special != ConstValSpecialRuntime) {
+            IrInstruction *result = ir_create_const(&ira->new_irb, source_instr->scope,
+                    source_instr->source_node, wanted_type);
+            result->value.type = wanted_type;
+            result->value.data.x_ptr.special = ConstPtrSpecialBaseArray;
+            result->value.data.x_ptr.mut = value->value.data.x_ptr.mut;
+            result->value.data.x_ptr.data.base_array.array_val = pointee;
+            result->value.data.x_ptr.data.base_array.elem_index = 0;
+            result->value.data.x_ptr.data.base_array.is_cstr = false;
+            return result;
+        }
+    }
+
+    IrInstruction *result = ir_build_cast(&ira->new_irb, source_instr->scope, source_instr->source_node,
+            wanted_type, value, CastOpBitCast);
+    result->value.type = wanted_type;
+    return result;
+}
+
+static IrInstruction *ir_resolve_ptr_of_array_to_slice(IrAnalyze *ira, IrInstruction *source_instr,
+        IrInstruction *value, TypeTableEntry *wanted_type)
+{
+    wanted_type = adjust_slice_align(ira->codegen, wanted_type, value->value.type->data.pointer.alignment);
+
+    if (instr_is_comptime(value)) {
+        ConstExprValue *pointee = const_ptr_pointee(ira->codegen, &value->value);
+        if (pointee->special != ConstValSpecialRuntime) {
+            assert(value->value.type->id == TypeTableEntryIdPointer);
+            TypeTableEntry *array_type = value->value.type->data.pointer.child_type;
+            assert(is_slice(wanted_type));
+            bool is_const = wanted_type->data.structure.fields[slice_ptr_index].type_entry->data.pointer.is_const;
+
+            IrInstruction *result = ir_create_const(&ira->new_irb, source_instr->scope,
+                    source_instr->source_node, wanted_type);
+            init_const_slice(ira->codegen, &result->value, pointee, 0, array_type->data.array.len, is_const);
+            result->value.data.x_struct.fields[slice_ptr_index].data.x_ptr.mut =
+                value->value.data.x_ptr.mut;
+            result->value.type = wanted_type;
+            return result;
+        }
+    }
+
+    IrInstruction *result = ir_build_cast(&ira->new_irb, source_instr->scope, source_instr->source_node,
+            wanted_type, value, CastOpPtrOfArrayToSlice);
+    result->value.type = wanted_type;
+    ir_add_alloca(ira, result, wanted_type);
+    return result;
+}
+
 static bool is_container(TypeTableEntry *type) {
     return type->id == TypeTableEntryIdStruct ||
         type->id == TypeTableEntryIdEnum ||
@@ -9937,6 +10023,35 @@ static IrInstruction *ir_analyze_cast(IrAnalyze *ira, IrInstruction *source_inst
         }
     }
 
+    // explicit *[N]T to [*]T
+    if (wanted_type->id == TypeTableEntryIdPointer &&
+        wanted_type->data.pointer.ptr_len == PtrLenUnknown &&
+        actual_type->id == TypeTableEntryIdPointer &&
+        actual_type->data.pointer.ptr_len == PtrLenSingle &&
+        actual_type->data.pointer.child_type->id == TypeTableEntryIdArray &&
+        actual_type->data.pointer.alignment >= wanted_type->data.pointer.alignment &&
+        types_match_const_cast_only(ira, wanted_type->data.pointer.child_type,
+            actual_type->data.pointer.child_type->data.array.child_type, source_node).id == ConstCastResultIdOk)
+    {
+        return ir_resolve_ptr_of_array_to_unknown_len_ptr(ira, source_instr, value, wanted_type);
+    }
+
+    // explicit *[N]T to []T
+    if (is_slice(wanted_type) &&
+        actual_type->id == TypeTableEntryIdPointer &&
+        actual_type->data.pointer.ptr_len == PtrLenSingle &&
+        actual_type->data.pointer.child_type->id == TypeTableEntryIdArray)
+    {
+        TypeTableEntry *slice_ptr_type = wanted_type->data.structure.fields[slice_ptr_index].type_entry;
+        assert(slice_ptr_type->id == TypeTableEntryIdPointer);
+        if (types_match_const_cast_only(ira, slice_ptr_type->data.pointer.child_type,
+            actual_type->data.pointer.child_type->data.array.child_type, source_node).id == ConstCastResultIdOk)
+        {
+            return ir_resolve_ptr_of_array_to_slice(ira, source_instr, value, wanted_type);
+        }
+    }
+
+
     // explicit cast from child type of maybe type to maybe type
     if (wanted_type->id == TypeTableEntryIdMaybe) {
         TypeTableEntry *wanted_child_type = wanted_type->data.maybe.child_type;
@@ -13150,6 +13265,13 @@ static TypeTableEntry *adjust_ptr_align(CodeGen *g, TypeTableEntry *ptr_type, ui
             ptr_type->data.pointer.bit_offset, ptr_type->data.pointer.unaligned_bit_count);
 }
 
+static TypeTableEntry *adjust_slice_align(CodeGen *g, TypeTableEntry *slice_type, uint32_t new_align) {
+    assert(is_slice(slice_type));
+    TypeTableEntry *ptr_type = adjust_ptr_align(g, slice_type->data.structure.fields[slice_ptr_index].type_entry,
+        new_align);
+    return get_slice_type(g, ptr_type);
+}
+
 static TypeTableEntry *adjust_ptr_len(CodeGen *g, TypeTableEntry *ptr_type, PtrLen ptr_len) {
     assert(ptr_type->id == TypeTableEntryIdPointer);
     return get_pointer_to_type_extra(g,

test/cases/cast.zig

@@ -384,3 +384,19 @@ test "const slice widen cast" {
 
     assert(@bitCast(u32, bytes) == 0x12121212);
 }
+
+test "single-item pointer of array to slice and to unknown length pointer" {
+    testCastPtrOfArrayToSliceAndPtr();
+    comptime testCastPtrOfArrayToSliceAndPtr();
+}
+
+fn testCastPtrOfArrayToSliceAndPtr() void {
+    var array = "ao" ++ "eu"; // TODO https://github.com/ziglang/zig/issues/1076
+    const x: [*]u8 = &array;
+    x[0] += 1;
+    assert(mem.eql(u8, array[0..], "boeu"));
+    const y: []u8 = &array;
+    y[0] += 1;
+    assert(mem.eql(u8, array[0..], "coeu"));
+}
+