[fpc-devel] probably incorrect debug-line-info generated by fpc 2.6.2 and trunk

[Jonas Maebe]

On 10 Nov 2013, at 23:05, Martin wrote:

> On 10/11/2013 21:55, Jonas Maebe wrote:
>> On 10 Nov 2013, at 22:42, Martin wrote:
>> 
>>> Why is the
>>> movl    %eax,-12(%ebp)
>>> generated at the start of i:=i+1
>>> 
>>> Why does a statement save an outdated value to memory?
>> Because the load back from memory that came right after it got removed by a peephole optimisation. Peephole optimisations are by definition local and have no clue about what happens next, and hence the store remains.
>> 
> Ok, i understand, but that would mean hat the save originally was intended for the "i := 1" statement.

The transformation that gets applied is

    movl const1,(mem1)
    movl (mem1),reg1
to:
    movl const1,reg1
    movl reg1,(mem1) }

The second instruction originally belonged to the second statement and hence has its line number info.

> I only wonder, if despite the fact that O1 does not guarantee, if in this case it would be worth to consider it a bug (and intend to fix it)?

If someone wants to change it, they're free to do so. My days of working on the peephole optimisers are over.


Jonas