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