How to get more fine-grained row/col debug info from clang?

I am writing software that does some rather complex static analysis and dynamic tracing of other programs. This program uses a lot of static DWARF information to assist in the tracing, including line/column info from the .debug_line DWARF section. In order for this program to have the accuracy that we need, it must have fine-grained and accurate row and column number information to be populated in the DWARF debugging info. Using clang I can force row and column info to be populated using the -g -Xclang -dwarf-column-info options together.

However, there are some cases where clang does not produce fine-grained enough column information. One particular instance is for for loops. Take the following example program which I will refer to as source01.c:

  1      
  2 int main ()
  3 {    
  4     int number1 = 10, number2 = 20;
  5     for (int i=0; i < 10; ++i) {                                                                                                                           
  6         number1++;
  7         number2++;
  8     }
  9     return 0;
 10 } 

I can compile it like so:

clang -g -Xclang -dwarf-column-info source01.c

Which produces the executable a.out. I then use dwarfdump to inspect how the row/column info has been populated:

dwarfdump a.out > dwarf_info

Taking a look at the .debug_line section, I see all of the row/col pairs that are contained in the debug info this executable:

.debug_line: line number info for a single cu
Source lines (from CU-DIE at .debug_info offset 0x0000000b):

<pc>        [row,col] NS BB ET PE EB IS= DI= uri: "filepath"
NS new statement, BB new basic block, ET end of text sequence
PE prologue end, EB epilogue begin
IA=val ISA number, DI=val discriminator value
0x004004f0  [   3, 0] NS uri: "/xxx/loop_01/source01.c"
0x004004fb  [   4, 5] NS PE
0x00400509  [   5,10] NS
0x0040051d  [   6, 9] NS
0x00400528  [   7, 9] NS
0x00400533  [   5,27] NS
0x00400548  [   9, 5] NS
0x0040054a  [   9, 5] NS ET

As you can see, there is the pair (5,10), which corresponds to int i=0;, and the pair (5,27), which corresponds to ++i. However, I would expect (and need) there to also be the pair (5,19), which would correspond to i < 10, but it isn't there. I have inspected the executable's instructions with objdump, and have confirmed that there are indeed instructions which correspond to the comparison i < 10 (Thus, it has not simply been "optimized away").

Do you have any intuition as to why clang would not populate this info? Or is there a way to force clang to produce more fine-grained column info? It seems like clang should have this capability, because the ASTs that clang generates have extremely fine-grained mappings between itself and the source code row and columns.

Thank you.

This isn't really a solution so much as an excuse but...

I believe the first entry (5, 8) includes code for both the initializer and condition statements in the for loop. When I compile a program with a for loop, these two statements end up in a contiguous range of addresses.

It would be nice to force clang to generate a separate entry for each statement, but I can't seem to find anything that would do that.