[llvm-dev] Understand the meaning of preds = %0

[Alberto Barbaro via llvm-dev]

Hi Bekket,
yes I think you are right :)

Thanks again
Alberto

Il giorno sab 27 apr 2019 alle ore 07:19 Bekket McClane <
bekket.mcclane at gmail.com> ha scritto:

> I think %0, in that context, means entry block
> So I guess it’s incorrect to say the BB, '<label>3’, has no predecessor
>
> Bekket
>
> On Apr 26, 2019, at 10:49 PM, Alberto Barbaro via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
> Hi all,
> I have seen in multiple cases that, usually at the beginning of the
> function. if a BranchInst is encountered the next block might have %0
> indicated as predecessor. I think it is a way to say "no predecessors
> found". Am I correct?
>
> Few examples just for clarifying what I mean:
>
> define noalias %struct.png_struct_def* @png_create_read_struct_2(i8*
> %user_png_ver, i8* %error_ptr, void (%struct.png_struct_def*, i8*)*
> %error_fn, void (%struct.png_struct_def*, i8*)* %warn_fn, i8* %mem_ptr, i8*
> (%struct.png_struct_def*, i64)* %malloc_fn, void (%struct.png_struct_def*,
> i8*)* %free_fn) #5 {
>   %1 = tail call noalias %struct.png_struct_def*
> @png_create_png_struct(i8* %user_png_ver, i8* %error_ptr, void
> (%struct.png_struct_def*, i8*)* %error_fn, void (%struct.png_struct_def*,
> i8*)* %warn_fn, i8* %mem_ptr, i8* (%struct.png_struct_def*, i64)*
> %malloc_fn, void (%struct.png_struct_def*, i8*)* %free_fn) #15
>   %2 = icmp eq %struct.png_struct_def* %1, null
>   br i1 %2, label %9, label %3
>
> ; <label>:3:                                      *; preds = %0*
>   %4 = getelementptr inbounds %struct.png_struct_def,
> %struct.png_struct_def* %1, i64 0, i32 15
> ...
> }
>
> define noalias %struct.png_struct_def* @png_create_read_struct(i8*
> %user_png_ver, i8* %error_ptr, void (%struct.png_struct_def*, i8*)*
> %error_fn, void (%struct.png_struct_def*, i8*)* %warn_fn) #5 {
>   %1 = tail call noalias %struct.png_struct_def*
> @png_create_png_struct(i8* %user_png_ver, i8* %error_ptr, void
> (%struct.png_struct_def*, i8*)* %error_fn, void (%struct.png_struct_def*,
> i8*)* %warn_fn, i8* null, i8* (%struct.png_struct_def*, i64)* null, void
> (%struct.png_struct_def*, i8*)* null) #15
>   %2 = icmp eq %struct.png_struct_def* %1, null
>   br i1 %2, label %png_create_read_struct_2.exit, label %3
>
> ; <label>:3:                                      *; preds = %0*
>   %4 = getelementptr inbounds %struct.png_struct_def,
> %struct.png_struct_def* %1, i64 0, i32 15
>  ...
> }
>
> Thanks
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