[sdcc-devel] [ sdcc-Bugs-519583 ] value in registers overwritten

[SourceForge.net <no...@so...>]

Bugs item #519583, was opened at 2002-02-18 15:17
Message generated for change (Comment added) made by epetrich
You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=100599&aid=519583&group_id=599

Category: Live range problems
>Group: fixed
>Status: Closed
>Resolution: Fixed
Priority: 9
Submitted By: Paul Stoffregen (pjs)
Assigned to: Johan Knol (johanknol)
Summary: value in registers overwritten

Initial Comment:
Here's some code to reproduce a register allocation bug
where a temporary value overwrites a variable, leading
to wrong results.  I have only been able to reproduce
the problem with large memory model.

The variable "next_block" is allocated to R2/R3 and is
used inside a for loop.  The loop's execution
overwrites R2/R3 each time the loop is re-run, which
causes the program to assign a wrong value if the
"next_block" variable is used after the first iteration
of the loop.

You can also download a copy of the code here:

http://www.pjrc.com/tmp/test.c




#ifndef SDCC_MODEL_LARGE
#error "This bug only shows up in large memory model"
#endif


struct simple_list_struct {
        unsigned int next;
};

static data unsigned int first_block=0;
static xdata at 0x7000 struct simple_list_struct p7;

void test(unsigned int val)
{
        unsigned int block, next_block;

        next_block = p7.next + 1234;    /* assigned to
r2/r3 */

        for (block = first_block; block != 0; block =
p7.next) {
                if (p7.next == val) {
                        p7.next = next_block;
                        return;
                }
                /* BUG: "block = p7.next" overwrites
r2/r3 */
        }
}



----------------------------------------------------------------------

>Comment By: Erik Petrich (epetrich)
Date: 2003-12-16 12:04

Message:
Logged In: YES 
user_id=635249

I have verified that the new live range code (specifically,
Klaus's 2003/10/28 cvs commit) has fixed this bug.


----------------------------------------------------------------------

Comment By: Johan Knol (johanknol)
Date: 2003-04-04 07:42

Message:
Logged In: YES 
user_id=63512

This wasn't a good fix. Infact it creates even bigger problems 
e.g. in gets.c where str[r567] and count[r01] weren't saved 
over the putchar() call after the return in the '\r' case where 
their liverange ended. Getchar() doesn't use these registers 
so it was never noticed, but still ...

Undid in SDCCloop.c:1.32

A better fix is on it's way.

----------------------------------------------------------------------

Comment By: Sandeep Dutta (sandeep)
Date: 2002-02-20 02:41

Message:
Logged In: YES 
user_id=1551

Fixed please update SDCCloop.c (fix). SDCCcflow.c (removed
temp fix)

----------------------------------------------------------------------

You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=100599&aid=519583&group_id=599