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

[Rafael Espíndola]

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
>>
>>
>>
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>
>
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