On 12/14, Daniel Sanders wrote:
>
>
> > On 14 Dec 2018, at 16:58, Doerfert, Johannes Rudolf via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> >
> > Hi Artem,
> >
> > 1) Please do not CC all the llvm lists you can find. llvm-dev is the one
> > for questions like this one, llvm-admin, mailman, bugs-admin, ... are
> > not.
> >
> > 2) Please attach the _full_ LLVM-IR you used, the ".txt" file you
> > attached is not complete and therefore not helpful. We can all
> > open/read ".ll" files and so should you. As long as you pass the -S
> > flag to opt (and clang in combination with -emit-llvm) you get human
> > readable (=plain text) LLVM-IR as outpu.
>
> According to the function group comments, the missing line seems to be:
> attributes #0 = { nounwind uwtable }
>
> @Артём: Hi,
> One other thing llvm-dev will need to know is the version of LLVM you're using. It looks like it isn't a recent version since load instructions changed a while back. For example:
> %0 = load i32* %a.addr, align 4
> from your .txt is now:
> %0 = load i32, i32* %a.addr, align 4
> in recent LLVM-IR.
Good catch!
The full IR (at least for custom builds) will also include the llvm and
clang version, another thing that is missing from the ".txt" ;)
> > 3) You should probably run something like:
> > clang -emit-llvm -S -O3 -mllvm -disable-llvm-optzns test.c -o test.ll
> > to get your initial IR. Then you probably want to continue with
> > opt -S -mem2reg -instcombine -simplifycfg test.ll -o test_clean.ll
> > to clean up the IR a bit (especially to remove the stack locations
> > introduced for variables and transform them into "proper SSA values".)
> > Finally you run your analyzes as you did before
> > opt -analyze -aa-eval -print-all-alias-modref-info test_clean.ll
> > to get your results. If you need help understand the results, please
> > let us know and provide enough information for us to comprehend your
> > problem. You should also take a look at the test.ll and test_clean.ll
> > and make sure you fully understand what the code representation
> > means. As I noted in the other thread, your example is to simple,
> > after the stack locations are promoted to registers, there is no
> > "ptra/ptrb" that could alias anymore.
> >
> > I hope this helps.
> >
> > Cheers,
> > Johannes
> >
> >
> >
> > On 12/14, Артём Вопилов via llvm-dev wrote:
> >> Dear LLVM developers,
> >>
> >> My name is Artem Vopilov, I am a student at TU Darmstadt. I am writing to you again to ask about Alias Analysis.
> >>
> >> Now I attached IR code and C code of program I analyze with Alias Analysis.
> >>
> >> Running commands "opt -analyze -aa-eval -print-all-alias-modref-info" and for printing sets of alias "opt -analyze -aa-eval -print-alias-sets" gives me the results, that in main function variables %a, %0, %2, %4 alias.
> >>
> >> However I expected from Alias Analysis to indicate that pointers which point to same memory location alias, namely, %ptra and %ptrb.
> >> I learnt from your last messages, that "A pointer is just a variable containing memory address, so pointer itself will never alias with other pointers, but the ‘pointee’ will alias with other memory addresses."
> >>
> >> My goal is to find sets of pointers, that point to the same memory locations.
> >> Am I right, that with Alias Analysis I cannot accomplish my aim? Is it possible to achieve it using LLVM?
> >> Thank you.
> >>
> >> I am looking forward to hearing from you!
> >>
> >> Respectfully yours,
> >> Artem Vopilov
> >
> >> ; ModuleID = '<stdin>'
> >> target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
> >> target triple = "x86_64-unknown-linux-gnu"
> >>
> >> ; Function Attrs: nounwind uwtable
> >> define i32 @main() #0 {
> >> entry:
> >> %retval = alloca i32, align 4
> >> %a = alloca i32, align 4
> >> %b = alloca i32, align 4
> >> %ptra = alloca i32*, align 8
> >> %ptrb = alloca i32*, align 8
> >> %temp = alloca i32, align 4
> >> %sum = alloca i32, align 4
> >> store i32 0, i32* %retval
> >> store i32 9, i32* %a, align 4
> >> store i32 7, i32* %b, align 4
> >> store i32* %a, i32** %ptra, align 8
> >> store i32* %a, i32** %ptrb, align 8
> >> %0 = load i32** %ptrb, align 8
> >> %1 = load i32* %0, align 4
> >> store i32 %1, i32* %b, align 4
> >> %2 = load i32** %ptrb, align 8
> >> store i32 4, i32* %2, align 4
> >> %3 = load i32* %a, align 4
> >> %4 = load i32** %ptrb, align 8
> >> %5 = load i32* %4, align 4
> >> %call = call i32 @addNumbers(i32 %3, i32 %5)
> >> store i32 %call, i32* %sum, align 4
> >> %6 = load i32* %sum, align 4
> >> ret i32 %6
> >> }
> >>
> >> ; Function Attrs: nounwind uwtable
> >> define i32 @addNumbers(i32 %a, i32 %b) #0 {
> >> entry:
> >> %a.addr = alloca i32, align 4
> >> %b.addr = alloca i32, align 4
> >> %result = alloca i32, align 4
> >> %notResult = alloca i32*, align 8
> >> store i32 %a, i32* %a.addr, align 4
> >> store i32 %b, i32* %b.addr, align 4
> >> store i32* %b.addr, i32** %notResult, align 8
> >> %0 = load i32* %a.addr, align 4
> >> %1 = load i32** %notResult, align 8
> >> %2 = load i32* %1, align 4
> >> %add = add nsw i32 %0, %2
> >> store i32 %add, i32* %result, align 4
> >> %3 = load i32* %result, align 4
> >> ret i32 %3
> >> }
> >
> >> #include <stdio.h>
> >>
> >>
> >> int addNumbers(int a, int b);
> >>
> >>
> >> int main()
> >> {
> >> int a = 9, b = 7;
> >> int *ptra, *ptrb;
> >> int temp;
> >> int sum;
> >>
> >> ptra = &a;
> >> ptrb = ptra;
> >> b = *ptrb;
> >>
> >> *ptrb = 4;
> >>
> >> sum = addNumbers(a, *ptrb);
> >>
> >> return sum;
> >> }
> >>
> >>
> >> int addNumbers(int a,int b)
> >> {
> >> int result;
> >> int *notResult;
> >>
> >> notResult = &b;
> >>
> >> result = a + *notResult;
> >>
> >> return result;
> >> }
> >>
> >
> >> _______________________________________________
> >> LLVM Developers mailing list
> >> llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>
> >> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev <http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev>
> >
> >
> > --
> >
> > Johannes Doerfert
> > Researcher
> >
> > Argonne National Laboratory
> > Lemont, IL 60439, USA
> >
> > jdoerfert at anl.gov <mailto:jdoerfert at anl.gov>
> > _______________________________________________
> > LLVM Developers mailing list
> > llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>
> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev <http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev>
--
Johannes Doerfert
Researcher
Argonne National Laboratory
Lemont, IL 60439, USA
jdoerfert at anl.gov
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