llvm dev - Jan 2011 - [LLVMdev] View variable-register map

Hello everyone,

I have started using LLVM only recently, so I'm a kind of a newbie. I'm 
using it to observe the effects of our path-sensitive analysis of the 
source code on register allocation.

I just wish to know if other than manually comparing the llc generated 
code with the source program, is there any other way of knowing which 
variables in the program are mapped to which registers? I was not able 
to find any suitable option for the same, so I'm wondering if there is a 
workaround.

Thank you!

------------
Vijayaraghavan Murali (Vijay)

On Fri, Jan 21, 2011 at 2:48 PM, Vijayaraghavan Murali
<m.vijay at nus.edu.sg> wrote:
> I just wish to know if other than manually comparing the llc generated
> code with the source program, is there any other way of knowing which
> variables in the program are mapped to which registers? I was not able
> to find any suitable option for the same, so I'm wondering if there is
a
> workaround.
Isn't this exactly one of the things debug information is for?
You'd need to compile with -g and somehow read the DWARF information
generated. As a bonus, this should work with gcc output too.

You'd still be comparing llc output with the source code[1], but you
no longer need to do it manually :).


[1]: Or the clang AST, I suppose.

Thank you Frits! I noticed the following lines in the dwarf output (run 
with -O2):

     .uleb128    40              # Offset
     .byte   134                     # DW_CFA_offset + Reg (6)
     .uleb128    4               # Offset
     .byte   135                     # DW_CFA_offset + Reg (7)
     .uleb128    3               # Offset
     .byte   131                     # DW_CFA_offset + Reg (3)

I think this is the closest to some sort of register "mapping", that I
*think* changes wrt to the live intervals in the program. But there is 
no information about variables to which the registers are mapped.

Actually, it's fine because I don't necessarily need the 
variable-register map. Even the number of registers used would suffice, 
which I can obtain from the above. But, can you just confirm if this is 
the result of register allocation and that the "Reg (#)" lines
represent
the different registers used?

Thank you once again!

Vijay


On 01/21/2011 10:03 PM, Frits van Bommel wrote:
> On Fri, Jan 21, 2011 at 2:48 PM, Vijayaraghavan Murali
> <m.vijay at nus.edu.sg>  wrote:
>> I just wish to know if other than manually comparing the llc generated
>> code with the source program, is there any other way of knowing which
>> variables in the program are mapped to which registers? I was not able
>> to find any suitable option for the same, so I'm wondering if there
is a
>> workaround.
>
> Isn't this exactly one of the things debug information is for?
> You'd need to compile with -g and somehow read the DWARF information
> generated. As a bonus, this should work with gcc output too.
>
> You'd still be comparing llc output with the source code[1], but you
> no longer need to do it manually :).
>
>
> [1]: Or the clang AST, I suppose.