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Alberto Barbaro via llvm-dev

2019-Dec-18 22:24 UTC

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

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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David Blaikie via llvm-dev

2019-Dec-18 22:30 UTC

head link

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

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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Robinson, Paul via llvm-dev

2019-Dec-18 23:02 UTC

head link

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

if (width == 0)
became
               %1 = icmp eq i32 %width, 0
which is straightforward; and
               else if (width > PNG_UINT_31_MAX)
became (assuming the constant is 0x7fffffff)
               %3 icmp slt i32 %width, 0
(note this is a signed comparison with 0, which is equivalent to the comparison
in the source)
and finally
               if (width > png_ptr->user_width_max)
became
               %8 = icmp ult i32 %7, %width
after loading the png_ptr field into %7 in the previous instruction.

Does that help?
--paulr

From: llvm-dev <llvm-dev-bounces at lists.llvm.org> On Behalf Of David
Blaikie via llvm-dev
Sent: Wednesday, December 18, 2019 5:30 PM
To: Alberto Barbaro <barbaro.alberto at gmail.com>
Cc: llvm-dev <llvm-dev at lists.llvm.org>
Subject: Re: [llvm-dev] Missing code depending on a #ifdef within the .ll file

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<mailto: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<mailto: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<mailto: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<mailto:llvm-dev at lists.llvm.org>
https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
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llvm dev - Dec 2019 - Missing code depending on a #ifdef within the .ll file

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

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

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