[llvm-dev] Missing code depending on a #ifdef within the .ll file

[David Blaikie via llvm-dev]

I'm sorry, I don't understand the question - the source code shows 3 calls
to png_warning (one of them from the if block you're interested in), and
the IR shows 3 calls to png_warning - so it looks like the body of the if
block is included in the IR you've shown?

On Wed, Dec 18, 2019 at 2:24 PM Alberto Barbaro <barbaro.alberto at gmail.com>
wrote:

> Hi David,
> My question is: why both #ifdef and #else branches are missing? I think at
> least one of the two should be present... In fact there is a case where the
> width could be greater then
> PNG_USER_WIDTH_MAX but not greater then PNG_UINT_31_MAX. That's why I was
> expecting at least one of the two...
>
> Thanks
> Alberto
>
>
>
> On Wed, Dec 18, 2019, 22:12 David Blaikie <dblaikie at gmail.com> wrote:
>
>> Not sure I understand the question - but usually a compiler would, on one
>> compilation, only compile one versoin of the code with one set of defines.
>>
>> There could be invalid code (it could literally be junk - or it could be
>> code that's only valid when the define is true/false, etc) in an
>> unreachable ifdef, so it doesn't make sense to compile it.
>>
>> On Wed, Dec 18, 2019 at 2:09 PM Alberto Barbaro via llvm-dev <
>> llvm-dev at lists.llvm.org> wrote:
>>
>>> Hi all,
>>> I have managed to compile libpng using wllvm and obtain the IR of
>>> pngpixel ( small tool which is part of libpng ).
>>>
>>> libpng has a function called png_check_IHDR:
>>>
>>> void /* PRIVATE */
>>> png_check_IHDR(png_const_structrp png_ptr,
>>>    png_uint_32 width, png_uint_32 height, int bit_depth,
>>>    int color_type, int interlace_type, int compression_type,
>>>    int filter_type)
>>> {
>>>    int error = 0;
>>>
>>>    /* Check for width and height valid values */
>>>    if (width == 0)
>>>    {
>>>       png_warning(png_ptr, "Image width is zero in IHDR");
>>>       error = 1;
>>>    }
>>>    else if (width > PNG_UINT_31_MAX)
>>>    {
>>>       png_warning(png_ptr, "Invalid image width in IHDR");
>>>       error = 1;
>>>    }
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>> * else   {#     ifdef PNG_SET_USER_LIMITS_SUPPORTED      if (width >
>>> png_ptr->user_width_max)#     else      if (width > PNG_USER_WIDTH_MAX)#
>>>   endif      {         png_warning(png_ptr, "Image width exceeds user limit
>>> in IHDR");         error = 1;      }   }*
>>> ...
>>> }
>>>
>>> Unfortunately the relative IR does not seem to have the branch
>>> highlighted in bold:
>>>
>>> ; Function Attrs: nounwind uwtable
>>> define void @png_check_IHDR(%struct.png_struct_def* noalias %png_ptr,
>>> i32 %width, i32 %height, i32 %bit_depth, i32 %color_type, i32
>>> %interlace_type, i32 %compression_type, i32 %filter_type) #5 {
>>>   *%1 = icmp eq i32 %width, 0*
>>>   br i1 %1, label %.thread, label %2
>>>
>>> .thread:                                          ; preds = %0
>>>   tail call void @png_warning(%struct.png_struct_def* %png_ptr, i8*
>>> getelementptr inbounds ([28 x i8], [28 x i8]* @.str50, i64 0, i64 0)) #15
>>>   br label %5
>>>
>>> ; <label>:2:                                      ; preds = %0
>>>   *%3 = icmp slt i32 %width, 0*
>>>   br i1 %3, label %4, label %5
>>>
>>> ; <label>:4:                                      ; preds = %2
>>>   tail call void @png_warning(%struct.png_struct_def* %png_ptr, i8*
>>> getelementptr inbounds ([28 x i8], [28 x i8]* @.str51, i64 0, i64 0)) #15
>>>   br label %5
>>>
>>> ; <label>:5:                                      ; preds = %4, %2,
>>> %.thread
>>>   %error.1 = phi i32 [ 1, %4 ], [ 0, %2 ], [ 1, %.thread ]
>>>   %6 = getelementptr inbounds %struct.png_struct_def,
>>> %struct.png_struct_def* %png_ptr, i64 0, i32 132
>>>   %7 = load i32, i32* %6, align 4, !tbaa !22
>>>   *%8 = icmp ult i32 %7, %width ; if (width > PNG_UINT_31_MAX)*
>>>   br i1 %8, label %9, label %10
>>>
>>> ; <label>:9:                                      ; preds = %5
>>>   tail call void @png_warning(%struct.png_struct_def* %png_ptr, i8*
>>> getelementptr inbounds ([39 x i8], [39 x i8]* @.str53, i64 0, i64 0)) #15
>>>   br label %10
>>>
>>> ; <label>:10:                                     ; preds = %9, %5
>>>   %error.3 = phi i32 [ 1, %9 ], [ %error.1, %5 ]
>>>   *%11 = icmp eq i32 %height, 0 ; first check on the height*
>>>   br i1 %11, label %.thread27, label %12
>>>
>>> Does anybody know why the else branch is completely missing?
>>>
>>> Thanks,
>>> Alberto
>>>
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> llvm-dev at lists.llvm.org
>>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>
>>
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