http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37895
Georg-Johann Lay <avr at gjlay dot de> changed:
What |Removed |Added
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CC| |eric.weddington at atmel
| |dot com
--- Comment #2 from Georg-Johann Lay <avr at gjlay dot de> 2011-03-12 13:01:13
UTC ---
I can not confirm the problems for WinAVR-20071221 (gcc 4.2.2)
With the following function
int32_t test_mul (void)
{
int32_t res = mul_16_8(0x1234, 0x56);
return res;
}
Both the generated code and the result of the computation (400760 in that
specific case) are as expected.
Presumably there is an error in your code outside the snippet (which we aren't
allowed to see), maybe some signed/undigned clashes, promotion problems,
overflows, etc.
The code compiles with
-S -Os -mmcu=atmega88 -fverbose-asm
to
<asm>
test_mul:
/* prologue: frame size=0 */
/* prologue end (size=0) */
ldi r24,lo8(4660) ; tmp43,
ldi r25,hi8(4660) ; tmp43,
ldi r18,lo8(86) ; tmp44,
movw r20,r24 ; , tmp43
/* #APP */
clr r24; ; res
clr r25; ; res
mul r20, r18; ; , tmp44
movw r22, r0; ; res
mul r21, r18; ; , tmp44
add r23, r0; ; res
adc r24, r1; ; res
clr __zero_reg__
/* #NOAPP */
/* epilogue: frame size=0 */
ret
</asm>
which is correct. gcc respects the early-clobber, i.e. the output operand
(r22-r25) does not overlap an input operand (r20-r21 and r18).
IMO this bug is invalid and can be closed.
Johann
