RE: [avr-gcc-list] optimizer

[Bernard Fouché]

As I written in my last post, I'm now using similar stuff. That will be a
maintenance pain and the code written is so gcc oriented that it becomes a
problem.

 Bernard

-----Message d'origine-----
De : Ben Mann [mailto:address@hidden
Envoyé : mercredi 24 novembre 2004 15:03
À : 'Haase Bjoern (PT-BEU/MKP5) *'; 'Bernard Fouché';
address@hidden
Objet : RE: [avr-gcc-list] optimizer


I can understand there's some challenge of making these sort of changes to
the RTL compiler. Nevertheless it seems that for embedded work this sort of
stuff is going to be quite important (speed and size always an issue...)

I realise this is not very helpful, but the best I could dream up so far was
a little macro to replace the compiler's casting:

//optimally cast a char to a long
#define CAST_CHAR2LONG(dest,src) \
    *((char*)&(dest)) = (src); \
    *((char*)&(dest)+1) = 0; \
    *((char*)&(dest)+2) = 0; \
    *((char*)&(dest)+3) = 0

long var;
...
CAST_CHAR2LONG(var,eeprom_read_byte((char *)ADDR));
//replaces var = eeprom_read_byte((char *)ADDR)

The code generated is (as you might imagine) substantially tighter and works
for local or global "var". However, the syntax sucks. I wonder if there's a
better way?

Ben Mann


-----Original Message-----
From: Haase Bjoern (PT-BEU/MKP5) * [mailto:address@hidden
Sent: Wednesday, 24 November 2004 8:56 PM
To: address@hidden; Bernard Fouché; address@hidden
Subject: AW: [avr-gcc-list] optimizer


Hi,

--snip!--

IMHO the possible benefit of a 32-> 4x8 splitting at the RTL level does not
really justify
the required amount of changes in the compiler.

Björn



-----Original Message-----
From: address@hidden [mailto:address@hidden
On Behalf Of Bernard Fouché
Sent: Wednesday, 24 November 2004 7:18 PM
To: address@hidden
Subject: [avr-gcc-list] optimizer


Hi.

I'm compiling with -Os for atmega64 with avr-gcc 3.4.2. When I have

uint32_t var;

var=(uint32_t)function_returning_an_int8_t();

the generated code is, for instance:

 var=(uint32_t)eeprom_read_byte((uint8_t *)EEPROM_PARM);
ldi     r24, 0x36       ; 54
ldi     r25, 0x00       ; 0
call    0xf9c0
eor     r25, r25
eor     r26, r26
eor     r27, r27
sts     0x046B, r24
sts     0x046C, r25
sts     0x046D, r26
sts     0x046E, r27

Could it be instead:
ldi     r24, 0x36       ; 54
ldi     r25, 0x00       ; 0
call    0xf9c0
sts     0x046B, r24
sts     0x046C, r1
sts     0x046D, r1
sts     0x046E, r1

That would spare 6 bytes...

  Bernard


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