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David Blaikie via llvm-dev

2021-Jul-30 16:46 UTC

[llvm-dev] Inline function not eventually inlined is removed

You're probably looking for some documentation about C inline semantics:
https://www.iar.com/knowledge/support/technical-notes/compiler/linker-error-undefined-external-for-inline-functions/

On Fri, Jul 30, 2021 at 9:16 AM Mariusz Sikora via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> Hello,
>
> I'm trying to understand why LLVM-12 is removing function which is
marked
> inline despite the fact it was not inlined inside caller. Caller function
> still has a call to inline function and compilation is failing because of a
> lack of the symbol.
>
> Looking at debug logs I see:
>
> Inliner visiting SCC: sort: 1 call sites.
>       Analyzing call of calculate... (caller:sort)
>       .
>       Cost: 960
>       Threshold: 487
>     NOT Inlining (cost=960, threshold=487), Call:   call void
> @calculate(i32* %a, i32* %b)
>
> Code:
> int global = 0;
> void inline calculate(int a[100], int b[100]) {
>     int i;
> #pragma unroll
>     for (i = 0; i < 50; i++) {
>         a[i] = b[i] + a[i];
>     }
> }
>
> int sort(int a[100], int b[100]) {
>     calculate(a, b);
>     return a[20] + b[30] + global;
> }
>
> cli: clang -O3 -c inline1.c -o inline1_clang.o
>
> ll file:
> ; Function Attrs: nounwind uwtable
>  define dso_local i32 @sort(i32* %a, i32* %b) local_unnamed_addr #0 {
> entry:
>    tail call void @calculate(i32* %a, i32* %b)
>    %arrayidx = getelementptr inbounds i32, i32* %a, i64 20
>    %0 = load i32, i32* %arrayidx, align 4, !tbaa !2
>    %arrayidx1 = getelementptr inbounds i32, i32* %b, i64 30
>    %1 = load i32, i32* %arrayidx1, align 4, !tbaa !2
>    %add = add nsw i32 %1, %0
>    %2 = load i32, i32* @global, align 4, !tbaa !2
>    %add2 = add nsw i32 %add, %2
>    ret i32 %add2
> }
>
> ; Function Attrs: inlinehint nounwind uwtable
>  declare dso_local void @calculate(i32*, i32*) local_unnamed_addr #1
>
> Thanks
> Mariusz Sikora
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
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Fangrui Song via llvm-dev

2021-Jul-30 17:15 UTC

head link

[llvm-dev] Inline function not eventually inlined is removed

On 2021-07-30, David Blaikie via llvm-dev wrote:>You're probably looking for some documentation about C inline semantics:
>https://www.iar.com/knowledge/support/technical-notes/compiler/linker-error-undefined-external-for-inline-functions/
Additional notes: I think the -fgnu89-inline & C99 inline semantics were
designed explicitly the way so that vague linkage
(https://itanium-cxx-abi.github.io/cxx-abi/abi/prop-72-comdat.html) can
be avoided. The C inline behaviors are like always explicit
instantiation in C++.

(Seems that GNU has extensions for weak symbols on the a.out binary
format. Otherwise, if a binary format has neither weak symbol nor
COMDAT, vague linkage is not representable.)
>On Fri, Jul 30, 2021 at 9:16 AM Mariusz Sikora via llvm-dev <
>llvm-dev at lists.llvm.org> wrote:
>
>> Hello,
>>
>> I'm trying to understand why LLVM-12 is removing function which is
marked
>> inline despite the fact it was not inlined inside caller. Caller
function
>> still has a call to inline function and compilation is failing because
of a
>> lack of the symbol.
>>
>> Looking at debug logs I see:
>>
>> Inliner visiting SCC: sort: 1 call sites.
>>       Analyzing call of calculate... (caller:sort)
>>       .
>>       Cost: 960
>>       Threshold: 487
>>     NOT Inlining (cost=960, threshold=487), Call:   call void
>> @calculate(i32* %a, i32* %b)
>>
>> Code:
>> int global = 0;
>> void inline calculate(int a[100], int b[100]) {
>>     int i;
>> #pragma unroll
>>     for (i = 0; i < 50; i++) {
>>         a[i] = b[i] + a[i];
>>     }
>> }
>>
>> int sort(int a[100], int b[100]) {
>>     calculate(a, b);
>>     return a[20] + b[30] + global;
>> }
>>
>> cli: clang -O3 -c inline1.c -o inline1_clang.o
>>
>> ll file:
>> ; Function Attrs: nounwind uwtable
>>  define dso_local i32 @sort(i32* %a, i32* %b) local_unnamed_addr #0 {
>> entry:
>>    tail call void @calculate(i32* %a, i32* %b)
>>    %arrayidx = getelementptr inbounds i32, i32* %a, i64 20
>>    %0 = load i32, i32* %arrayidx, align 4, !tbaa !2
>>    %arrayidx1 = getelementptr inbounds i32, i32* %b, i64 30
>>    %1 = load i32, i32* %arrayidx1, align 4, !tbaa !2
>>    %add = add nsw i32 %1, %0
>>    %2 = load i32, i32* @global, align 4, !tbaa !2
>>    %add2 = add nsw i32 %add, %2
>>    ret i32 %add2
>> }
>>
>> ; Function Attrs: inlinehint nounwind uwtable
>>  declare dso_local void @calculate(i32*, i32*) local_unnamed_addr #1
>>
>> Thanks
>> Mariusz Sikora
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>_______________________________________________
>LLVM Developers mailing list
>llvm-dev at lists.llvm.org
>https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev

Mariusz Sikora via llvm-dev

2021-Aug-02 17:05 UTC

head link

[llvm-dev] Inline function not eventually inlined is removed

I'm just trying to understand is this _Code_ undefined behavior or this is
a bug in LLVM? Because why LLVM is removing functions without inlining it?
For example GCC is not removing function event after inlining it.

On Fri, Jul 30, 2021 at 7:16 PM Fangrui Song <maskray at google.com>
wrote:
> On 2021-07-30, David Blaikie via llvm-dev wrote:
> >You're probably looking for some documentation about C inline
semantics:
> >
>
https://www.iar.com/knowledge/support/technical-notes/compiler/linker-error-undefined-external-for-inline-functions/
>
> Additional notes: I think the -fgnu89-inline & C99 inline semantics
were
> designed explicitly the way so that vague linkage
> (https://itanium-cxx-abi.github.io/cxx-abi/abi/prop-72-comdat.html) can
> be avoided. The C inline behaviors are like always explicit
> instantiation in C++.
>
> (Seems that GNU has extensions for weak symbols on the a.out binary
> format. Otherwise, if a binary format has neither weak symbol nor
> COMDAT, vague linkage is not representable.)
>
> >On Fri, Jul 30, 2021 at 9:16 AM Mariusz Sikora via llvm-dev <
> >llvm-dev at lists.llvm.org> wrote:
> >
> >> Hello,
> >>
> >> I'm trying to understand why LLVM-12 is removing function
which is
> marked
> >> inline despite the fact it was not inlined inside caller. Caller
> function
> >> still has a call to inline function and compilation is failing
because
> of a
> >> lack of the symbol.
> >>
> >> Looking at debug logs I see:
> >>
> >> Inliner visiting SCC: sort: 1 call sites.
> >>       Analyzing call of calculate... (caller:sort)
> >>       .
> >>       Cost: 960
> >>       Threshold: 487
> >>     NOT Inlining (cost=960, threshold=487), Call:   call void
> >> @calculate(i32* %a, i32* %b)
> >>
> >> Code:
> >> int global = 0;
> >> void inline calculate(int a[100], int b[100]) {
> >>     int i;
> >> #pragma unroll
> >>     for (i = 0; i < 50; i++) {
> >>         a[i] = b[i] + a[i];
> >>     }
> >> }
> >>
> >> int sort(int a[100], int b[100]) {
> >>     calculate(a, b);
> >>     return a[20] + b[30] + global;
> >> }
> >>
> >> cli: clang -O3 -c inline1.c -o inline1_clang.o
> >>
> >> ll file:
> >> ; Function Attrs: nounwind uwtable
> >>  define dso_local i32 @sort(i32* %a, i32* %b) local_unnamed_addr
#0 {
> >> entry:
> >>    tail call void @calculate(i32* %a, i32* %b)
> >>    %arrayidx = getelementptr inbounds i32, i32* %a, i64 20
> >>    %0 = load i32, i32* %arrayidx, align 4, !tbaa !2
> >>    %arrayidx1 = getelementptr inbounds i32, i32* %b, i64 30
> >>    %1 = load i32, i32* %arrayidx1, align 4, !tbaa !2
> >>    %add = add nsw i32 %1, %0
> >>    %2 = load i32, i32* @global, align 4, !tbaa !2
> >>    %add2 = add nsw i32 %add, %2
> >>    ret i32 %add2
> >> }
> >>
> >> ; Function Attrs: inlinehint nounwind uwtable
> >>  declare dso_local void @calculate(i32*, i32*) local_unnamed_addr
#1
> >>
> >> Thanks
> >> Mariusz Sikora
> >> _______________________________________________
> >> LLVM Developers mailing list
> >> llvm-dev at lists.llvm.org
> >> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> >>
>
> >_______________________________________________
> >LLVM Developers mailing list
> >llvm-dev at lists.llvm.org
> >https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
-- 
Pozdrawiam
Mariusz Sikora
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llvm dev - Aug 2021 - Inline function not eventually inlined is removed

[llvm-dev] Inline function not eventually inlined is removed

[llvm-dev] Inline function not eventually inlined is removed

[llvm-dev] Inline function not eventually inlined is removed