Please send questions to mspgcc-users@lists.sourceforge.net and not to me
directly.
An instruction sequence like you show would occur if the compiler had to
treat r15 as a pointer to a byte rather than an int (viz., a packed
structure) and therefore needed to fetch the bytes independently and
reconstruct the 16-bit length and pointer values. Presumably the reason it
did so would be revealed by the C code for the function body or compiler
flags.
On Fri, Nov 16, 2012 at 5:27 AM, scalpel4k <scalpe...@gmail.com> wrote:
> Hallo Peter,
>
> I am using the latest git snapshot of your mspgcc. Right now I comb through
> the assembly the compiler is producing for my code. At one point I am a bit
> confused.
>
> I have declared this array structure:
>
> typedef struct {
> uint16_t size;
> uint8_t * data;
> } uint8Array_t;
>
>
> When I use that struct in the following way:
>
> void someMethod(uint8Array_t * dataArray) {....}
>
> using the 2 struct members (size and data) in that method translates into
> this
> assembly code:
>
> 14: 5d 4f 02 00 mov.b 2(r15), r13 ;0x0002(r15)
> 18: 5e 4f 03 00 mov.b 3(r15), r14 ;0x0003(r15)
> 1c: 8e 10 swpb r14
> 1e: 0e dd bis r13, r14
> 20: 6d 4f mov.b @r15, r13
> 22: 5f 4f 01 00 mov.b 1(r15), r15 ;0x0001(r15)
> 26: 8f 10 swpb r15
> 28: 0f dd bis r13, r15
>
> Am I missing something important here? I thought it was a lot simpler .....
>
> As far as I understand, r15 should contain the address to the struct that
> can
> be anywhere in RAM, right? So, I would have thought something like the
> following would have been a proper translation:
>
> mov.w @r15+, r14
> mov.w @r15, r13
>
> Or does r15 point to the parameter list on the stack? Even in that case I
> don't quite understand the use of byte operations.
>
> Alternatively, when I provide dataArray directly (not as pointer) to a
> method
> the assembly code looks ok to me. The generated assembly code uses the
> stackpointer to access the struct, just as I would have expected.
>
> What do you think, am I really missing something? Btw. I don't use CPUX
> right
> now, just in case that makes some difference.
>
> bye Michi
>
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