diff options
Diffstat (limited to 'tcg/tcg.h')
| -rw-r--r-- | tcg/tcg.h | 38 |
1 files changed, 30 insertions, 8 deletions
@@ -376,14 +376,36 @@ static inline unsigned get_alignment_bits(TCGMemOp memop) typedef tcg_target_ulong TCGArg; -/* Define a type and accessor macros for variables. Using pointer types - is nice because it gives some level of type safely. Converting to and - from intptr_t rather than int reduces the number of sign-extension - instructions that get implied on 64-bit hosts. Users of tcg_gen_* don't - need to know about any of this, and should treat TCGv as an opaque type. - In addition we do typechecking for different types of variables. TCGv_i32 - and TCGv_i64 are 32/64-bit variables respectively. TCGv and TCGv_ptr - are aliases for target_ulong and host pointer sized values respectively. */ +/* Define type and accessor macros for TCG variables. + + TCG variables are the inputs and outputs of TCG ops, as described + in tcg/README. Target CPU front-end code uses these types to deal + with TCG variables as it emits TCG code via the tcg_gen_* functions. + They come in several flavours: + * TCGv_i32 : 32 bit integer type + * TCGv_i64 : 64 bit integer type + * TCGv_ptr : a host pointer type + * TCGv : an integer type the same size as target_ulong + (an alias for either TCGv_i32 or TCGv_i64) + The compiler's type checking will complain if you mix them + up and pass the wrong sized TCGv to a function. + + Users of tcg_gen_* don't need to know about any of the internal + details of these, and should treat them as opaque types. + You won't be able to look inside them in a debugger either. + + Internal implementation details follow: + + Note that there is no definition of the structs TCGv_i32_d etc anywhere. + This is deliberate, because the values we store in variables of type + TCGv_i32 are not really pointers-to-structures. They're just small + integers, but keeping them in pointer types like this means that the + compiler will complain if you accidentally pass a TCGv_i32 to a + function which takes a TCGv_i64, and so on. Only the internals of + TCG need to care about the actual contents of the types, and they always + box and unbox via the MAKE_TCGV_* and GET_TCGV_* functions. + Converting to and from intptr_t rather than int reduces the number + of sign-extension instructions that get implied on 64-bit hosts. */ typedef struct TCGv_i32_d *TCGv_i32; typedef struct TCGv_i64_d *TCGv_i64; |