[llvm-dev] Help with bitcast instruction

[Craig Topper via llvm-dev]

bitcast is an LLVM IR instruction. You can find its description here
https://llvm.org/docs/LangRef.html#bitcast-to-instruction

~Craig


On Sun, Mar 10, 2019 at 12:18 AM Alberto Barbaro via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Hi,
> I'm playing with the IR of pngpixel and I encountered this instruction:
>
> call void bitcast (void (%struct.png_struct_def.68*, i8*, i8*
> (%struct.png_struct_def.68*, i64)*, void (%struct.png_struct_def.68*,
> i8*)*)* @png_set_mem_fn to void (%struct.png_struct_def*, i8*, i8*
> (%struct.png_struct_def*, i64)*, void (%struct.png_struct_def*,
> i8*)*)*)(%struct.png_struct_def* %create_struct, i8* %mem_ptr, i8*
> (%struct.png_struct_def*, i64)* %malloc_fn, void (%struct.png_struct_def*,
> i8*)* %free_fn) #15
>
> I would like to understand where bitcast is defined because it is not
> defined within libpng. I also noticed that the @ is not present, what does
> the missing @ mean? I guess it must be an LLVM function.
>
> The bitcast operation seems to represent the following C code:
>
> if (png_ptr != NULL)
>    {
>       png_ptr->mem_ptr = mem_ptr;
>       png_ptr->malloc_fn = malloc_fn;
>       png_ptr->free_fn = free_fn;
>    }
>
>
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