Alberto Barbaro via llvm-dev
2019-Apr-27 05:49 UTC
[llvm-dev] Understand the meaning of preds = %0
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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Bekket McClane via llvm-dev
2019-Apr-27 06:19 UTC
[llvm-dev] Understand the meaning of preds = %0
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 > _______________________________________________ > 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/20190426/40879363/attachment.html>
Alberto Barbaro via llvm-dev
2019-Apr-27 06:40 UTC
[llvm-dev] Understand the meaning of preds = %0
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 > _______________________________________________ > 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/20190427/c8c652b0/attachment.html>