Alberto Barbaro via llvm-dev
2019-Dec-18 22:08 UTC
[llvm-dev] Missing code depending on a #ifdef within the .ll file
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
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David Blaikie via llvm-dev
2019-Dec-18 22:12 UTC
[llvm-dev] Missing code depending on a #ifdef within the .ll file
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 >-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20191218/dc8edaf8/attachment.html>
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 >> >-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20191218/e5c02ff9/attachment.html>