Re: [avr-gcc-list] Need help compiling testcase with gcc 3.3.5 or 3.4.3

[Andy Hutchinson]

The size issue is almost certaintly caused by the peephole optimisation.

Initial instruction length guesses are set as attributes in avr.md. 
Basically this keep jumps in range and estimates should be for worst case.
When the registers and operands are eventually determined, the length 
gets adjusted by the routines inside avr.c - again to get the jump 
range/type correct.

Peephole optimisation changes things really late in the process - 
peepholes that create asm code (rather than RTL) do not change lengths - 
so it should be wrong.

On the otherhand there could well be a few mistakes in length 
calculations! It is unlikely to cause any problems. If estimates are too 
high jumps might be "bigger" than they need to be - but they will still 
hit the right spot as labels are used. Low estimates may cause jump out 
of range problems or bad code with a skip.
Its worth keeping an  eye on.

I think -mdebug adds instrction length and cost estimates to .lst file.

address@hidden wrote:

> On Saturday 29 January 2005 11:41, Andy Hutchinson wrote:
>
> > Many Thanks to summarize 3.4.3 has same response as WINAVR 3.3.1
> >
> > I've filed bug report on 4.0 for lack of loop reversal - but it will be
> > treated as missed optimisation unless other ports take a big hit.
> >
> > gcc-avr has problem with pattern matching - This happens at least back
> > to 3.3.1
> >
> > The AVR.MD RTL peephole turns sign status tests (Rx<=0) + jump into (RX
> > & -32768) +jump. Then  "*sbrx_and_branchhi" turns this into SBRS.
> > Unfortunately this occurs before  the potentially more efficient code
> > peephole ((Rx=Rx-1)<=0)+jump is tried.
> >
> > Somehow I have to figure out how to catch things before 1st peephole
> > grabs the sign test. Probabley another RTL peephole and delete the old
> > code ones.
>
>
> Interesting thing with avr-gcc 4.0 -- wrong size in comment.
> Look:
>     ...
> testloop1:
> /* prologue: frame size=0 */
>         push r28
>         push r29
> /* prologue end (size=2) */
>         ldi r28,lo8(10)
>         ldi r29,hi8(10)
> .L2:
>         call foo
>         sbiw r28,1
>         brne .L2
> /* epilogue: frame size=0 */
>         pop r29
>         pop r28
>         ret
> /* epilogue end (size=3) */
> /* function testloop1 size 12 (7) */
>
> Similar error is in 3.3.4 also.
>
> I have send a message to gcc bug-list (#19684).
>
>
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