[cfe-dev] Why do "Uses" always point to self?

[Yaron Keren]

r203364
http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20140303/207915.html


The for code could be ranged

for (llvm::user i : F->users())
  if (Instruction *Inst = dyn_cast<Instruction>(i)) {

and the next code segment could be

for (llvm::use i : pi->uses()) {





2014-04-30 16:15 GMT+03:00 Rafael Espíndola <rafael.espindola at gmail.com>:

> I think so. Chandler, is this changed in r203364, no?
>
> On 30 April 2014 06:13, Yaron Keren <yaron.keren at gmail.com> wrote:
> > Thanks, using getUser() indeed works.  I am still confused by the
> example in
> > the LLVM Programmer's Manual that says
> >
> >
> http://www.llvm.org/docs/ProgrammersManual.html#iterating-over-def-use-use-def-chains
> >
> > Finding all of the instructions that use foo is as simple as iterating
> over
> > the def-use chain of F:
> >
> > Function *F = ...;
> >
> > for (Value::use_iterator i = F->use_begin(), e = F->use_end(); i != e;
> ++i)
> >   if (Instruction *Inst = dyn_cast<Instruction>(*i)) {
> >
> > won't (*i) get us back the llvm::Value (def) which is F ?
> > should the example code read
> >
> >   if (Instruction *Inst = dyn_cast<Instruction>(i->getUser())) {
> >
> > Yaron
> >
> >
> > 2014-04-30 12:49 GMT+03:00 James Molloy <james at jamesmolloy.co.uk>:
> >
> >> Hi Yaron,
> >>
> >> A Use is an edge between a Value and its users. If you dereference a
> Use,
> >> you get the Value it points to (which of course is your function - the
> thing
> >> that "is being used" is F). What you want is the *user* of that use, so
> you
> >> need to call U.getUser().
> >>
> >> http://llvm.org/docs/doxygen/html/classllvm_1_1Use.html#details
> >>
> >> Cheers,
> >>
> >> James
> >
> >
> >
> > On 30 April 2014 10:01, Yaron Keren <yaron.keren at gmail.com> wrote:
> >>
> >> Hi,
> >>
> >> I use the code from the LLVM programmer manual
> >>
> >>
> >>
> http://www.llvm.org/docs/ProgrammersManual.html#iterating-over-def-use-use-def-chains
> >>
> >>   for (llvm::Value::use_iterator i = F->use_begin(), e = F->use_end(); i
> >> != e; ++i) {
> >>
> >> to iterate over Function '_Z2tcv' uses in the trivial module
> >>
> >> ; ModuleID = 'module'
> >> target datalayout = "e-m:w-p:32:32-i64:64-f80:32-n8:16:32-S32"
> >> target triple = "i686-pc-windows-gnu"
> >>
> >> ; Function Attrs: nounwind
> >> define void @_Z2tcv() #0 {
> >> entry:
> >>   ret void
> >> }
> >>
> >> ; Function Attrs: nounwind
> >> define i32 @main() #0 {
> >> entry:
> >>   call void @_Z2tcv()
> >>   ret i32 0
> >> }
> >>
> >> attributes #0 = { nounwind "less-precise-fpmad"="false"
> >> "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf"
> >> "no-infs-fp-math"="false" "no-nans-fp-math"="false"
> >> "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft
> >> -float"="false" }
> >>
> >> !llvm.ident = !{!0}
> >>
> >> !0 = metadata !{metadata !"clang version 3.5.0 (207351)"}
> >>
> >> _Z2tcv has indeed one use, as expected, but the use is not a call
> >> instruction as in main as expected so
> >>
> >>  llvm::Instruction *Inst = dyn_cast<llvm::Instruction>(*i)
> >>
> >> results in NULL.
> >>
> >> Examining the use value with the code
> >>
> >> const llvm::Use &U = (*i);
> >>
> >> indeed shows that U is same value as F, so F uses itself??
> >>
> >> I have seen this in more complicated cases, the number of uses is as
> >> expected but the uses always point to the function or variable and not
> the
> >> real users.
> >>
> >> What is wrong?
> >>
> >> Thanks, Yaron
> >>
> >>
> >>
> >> _______________________________________________
> >> cfe-dev mailing list
> >> cfe-dev at cs.uiuc.edu
> >> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev
> >>
> >
> >
> > _______________________________________________
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> >
>
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