[LLVMdev] what is the Line number of Phi Node with addr2line

[Eric Lu]

Hey, Daniel

  Is it better to instrument in the CodeGen phase ? I am now doing it in
the opt phases, and it seems a little complex when instrument phi nodes,
because I have to decide where the load operation should be if there are no
phi nodes.

%indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]

It may load 0 or %indvars.iv.next, I have to add checkLoad(addr, size) in
different BBs for different incoming value.

I guess in CodeGen Phase, the code have been changed back to code with
load/store already.

Are there examples to show me how to instrument in the CodeGen Phase?

On Wed, Apr 22, 2015 at 1:23 PM, Daniel Berlin <dberlin at dberlin.org> wrote:

> reg2mem does not eliminate phi nodes the way codegen does, it just
> converts ssa values to non-ssa values.
>
> It's not the same thing.
>
>
> On Tue, Apr 21, 2015 at 10:14 PM, Eric Lu <eirc.lew at gmail.com> wrote:
> > By the way. When I remove these phi nodes with -reg2mem, some new load
> > operations will be inserted, but when I try cache load operations with:
> > visitFunction
> > visitLoadInst
> > It seems we can't see these new load operations.
> >
> > On Wed, Apr 22, 2015 at 1:10 PM, Eric Lu <eirc.lew at gmail.com> wrote:
> >>
> >> Hi, Daniel
> >>
> >> I want to profile load/store operations, in order to reduce the overhead
> >> of profiling, I try to instrument the optimized llvm ir, which has phi
> >> nodes.
> >>
> >> BTW, when the value of some load/store operations may have multi-source,
> >> then the load will be translated into phi nodes, and all phi nodes are
> >> placed in the front of BB. Sometimes, the position is not where the load
> >> happens, is there any way to figure out where the load should be
> placed?( If
> >> the phi node translated back to load operations)
> >>
> >> Best Regards!
> >> Eric Lew
> >>
> >> On 周三, 4月 22, 2015 at 12:24 下午, Daniel Berlin <dberlin at dberlin.org>
> wrote:
> >>
> >> Hey Eric,
> >> phi nodes don't exist for real, so you can't.
> >> The are removed by PHI elimination as part of codegen.
> >>
> >> What are you trying to achieve?
> >>
> >>
> >>
> >>
> >> On Tue, Apr 21, 2015 at 9:12 PM, Eric Lu <eirc.lew at gmail.com> wrote:
> >> > Hi, all
> >> >
> >> >    When compiling a program with -g -O0, and if we have a PC, then
> with
> >> > addr2line, we can get the line number of the instruction.
> >> >
> >> > My quesions are:  what is the result of Phi node instruction, can we
> get
> >> > the
> >> > similar results ?
> >> >
> >> > --
> >> > Best Regards!
> >> > Eric Lew
> >> >
> >> > _______________________________________________
> >> > LLVM Developers mailing list
> >> > LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> >> > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
> >> >
> >
> >
> >
> >
> > --
> > Best Regards!
> > Eric Lew
>



-- 
Best Regards!
Eric Lew
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