add integer literal to pointer explicit cast

closes #227

src/ir.cpp

@@ -6424,6 +6424,27 @@ static IrInstruction *ir_analyze_int_to_ptr(IrAnalyze *ira, IrInstruction *sourc
     return result;
 }
 
+static IrInstruction *ir_analyze_int_lit_to_ptr(IrAnalyze *ira, IrInstruction *source_instr,
+        IrInstruction *target, TypeTableEntry *wanted_type)
+{
+    assert(wanted_type->id == TypeTableEntryIdPointer);
+
+    ConstExprValue *val = ir_resolve_const(ira, target, UndefBad);
+    if (!val)
+        return ira->codegen->invalid_instruction;
+
+    TypeTableEntry *usize_type = ira->codegen->builtin_types.entry_usize;
+    if (!ir_num_lit_fits_in_other_type(ira, target, usize_type))
+        return ira->codegen->invalid_instruction;
+
+    IrInstruction *result = ir_create_const(&ira->new_irb, source_instr->scope,
+            source_instr->source_node, wanted_type, val->depends_on_compile_var);
+    result->value.data.x_ptr.base_ptr = nullptr;
+    result->value.data.x_ptr.index = bignum_to_twos_complement(&val->data.x_bignum);
+    result->value.data.x_ptr.special = ConstPtrSpecialRuntime;
+    return result;
+}
+
 static IrInstruction *ir_analyze_int_to_enum(IrAnalyze *ira, IrInstruction *source_instr,
         IrInstruction *target, TypeTableEntry *wanted_type)
 {
@@ -6491,6 +6512,13 @@ static IrInstruction *ir_analyze_cast(IrAnalyze *ira, IrInstruction *source_inst
         return ir_analyze_int_to_ptr(ira, source_instr, value, wanted_type);
     }
 
+    // explicit cast from number literal to pointer
+    if (wanted_type_canon->id == TypeTableEntryIdPointer &&
+        (actual_type_canon->id == TypeTableEntryIdNumLitInt))
+    {
+        return ir_analyze_int_lit_to_ptr(ira, source_instr, value, wanted_type);
+    }
+
     // explicit widening or shortening cast
     if ((wanted_type_canon->id == TypeTableEntryIdInt &&
         actual_type_canon->id == TypeTableEntryIdInt) ||

test/cases/cast.zig

@@ -8,3 +8,10 @@ fn intToPtrCast() {
     const z = usize(y);
     assert(z == 13);
 }
+
+fn numLitIntToPtrCast() {
+    @setFnTest(this);
+
+    const vga_mem = (&u16)(0xB8000);
+    assert(usize(vga_mem) == 0xB8000);
+}