http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47590
Summary: var tracking produces wrong debug in code where
optimization is turned off using pragma
Product: gcc
Version: 4.6.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: debug
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: harihar...@picochip.com
Created attachment 23216
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=23216
The source code
In the attached testcase #pragma has been used to turn optimization off (The
file is otherwise compiled at -Os). By turning off optimization, we expected to
be able to get better debug experience. We noticed that the variable n in the
function "fn" takes the following values, if you step through the function.
4 3 0 2 1 5 0 10 -1
which is obviously wrong.
I reckon the problem lies in var-tracking. Our dwarf reader tells me that the
value of "n" could be found in the following places.
Name: n
Location:
[29, 48) : DW_OP_reg1
[48, 66) : DW_OP_reg4
[66, 102) : DW_OP_fbreg[-6]
[102, 112) : DW_OP_reg4
I will attach the address encoded assembly so you can see that var-tracking
gets it wrong. If i compile the whole file at -O0, the dwarf information the
dwarf gets it right.
Name: n
Location: DW_OP_fbreg[-6]
In this particular case, adding -fno-var-tracking has the same effect in
correcting the debug information.
I guess there are 2 things that could be done.
1. Find out the problem in var-tracking in this case and fix it.
2. Turn off var-tracking for functions where optimization is turned off using
attributes/pragmas.
Please let me know if you need any other information on this. I tried all my
experiments with master (as of 2-feb-2011). The experiments were conducted on
picochip (picochip-unknown-none target triplet).
Thanks
Hari
