Hi, Using this option I do get all the vars as may alias ie MayAlias: i32* %j.0, i32* %k MayAlias: i32* %i.0, i32* %k MayAlias: i32* %i.0, i32* %j.0 Is there any other analysis which will give them as must aliases. Actually what I want to do is implement a flow sensitive points-to(not alias) analysis and then use that information for some optimizations like PRE. Will that be possible? Duncan Sands wrote:> Hi Ambika, > >> to compile it to bitcode I give the following command : >> >> llvm-gcc -emit-llvm -c -o s.bc s.c >> >> and then I run different alias analysis passes like -anders-aa, >> -basicaa using following: >> >> opt -anders-aa -aa-eval -print-all-alias-modref-info s.bc > > alias analysis will work poorly if you don't run any optimizers. > The alias analysis passes assume that at least some basic optimizations > have been done. Try compiling like this: > > llvm-gcc -emit-llvm -c -o s.bc s.c -O1 > > Ciao, > > Duncan.
Hi Ambika,> Using this option I do get all the vars as may alias ie > > MayAlias: i32* %j.0, i32* %k > MayAlias: i32* %i.0, i32* %k > MayAlias: i32* %i.0, i32* %j.0 > > Is there any other analysis which will give them as must aliases.at -O1 these variables are entirely eliminated here. I'm surprised they aren't eliminated for you. Ciao, Duncan. PS: $ cat ambika.c int main() { int *i,*j,k; i=&k; j=&k; k=4; printf("%d,%d,%d",*i,*j,k); return 0; } $ llvm-gcc -S -O1 -emit-llvm -o - ambika.c ambika.c: In function ‘main’: ambika.c:7: warning: incompatible implicit declaration of built-in function ‘printf’ ; ModuleID = 'ambika.c' target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64" target triple = "x86_64-unknown-linux-gnu" @.str = private constant [9 x i8] c"%d,%d,%d\00", align 1 ; <[9 x i8]*> [#uses=1] define i32 @main() nounwind { entry: %0 = tail call i32 (i8*, ...)* @printf(i8* getelementptr inbounds ([9 x i8]* @.str, i64 0, i64 0), i32 4, i32 4, i32 4) nounwind ; <i32> [#uses=0] ret i32 0 } declare i32 @printf(i8* nocapture, ...) nounwind
Hi, Using this option I do get all the vars as may alias ie MayAlias: i32* %j.0, i32* %k MayAlias: i32* %i.0, i32* %k MayAlias: i32* %i.0, i32* %j.0 Is there any other analysis which will give them as must aliases. Actually what I want to do is implement a flow sensitive points-to(not alias) analysis and then use that information for some optimizations like PRE. Will that be possible?> > Duncan Sands wrote: >> Hi Ambika, >> >>> to compile it to bitcode I give the following command : >>> >>> llvm-gcc -emit-llvm -c -o s.bc s.c >>> >>> and then I run different alias analysis passes like -anders-aa, >>> -basicaa using following: >>> >>> opt -anders-aa -aa-eval -print-all-alias-modref-info s.bc >> >> alias analysis will work poorly if you don't run any optimizers. >> The alias analysis passes assume that at least some basic optimizations >> have been done. Try compiling like this: >> >> llvm-gcc -emit-llvm -c -o s.bc s.c -O1 >> >> Ciao, >> >> Duncan. > >
Hi,
I actually used the example mentioned by Török
int main(int argc, char **argv)
{
int *i=0,*j=0,k;
if (argc > 1) {
i=&k;
} else {
j=&k;
}
k=4;
printf("%d,%d,%d,%p,%p",*i,*j,k,i,j);
return 0;
}
Duncan Sands wrote:> Hi Ambika,
>
>> Using this option I do get all the vars as may alias ie
>>
>> MayAlias: i32* %j.0, i32* %k
>> MayAlias: i32* %i.0, i32* %k
>> MayAlias: i32* %i.0, i32* %j.0
>>
>> Is there any other analysis which will give them as must aliases.
>
> at -O1 these variables are entirely eliminated here. I'm surprised
> they aren't eliminated for you.
>
> Ciao,
>
> Duncan.
>
> PS:
>
> $ cat ambika.c
> int main()
> {
> int *i,*j,k;
> i=&k;
> j=&k;
> k=4;
> printf("%d,%d,%d",*i,*j,k);
> return 0;
> }
> $ llvm-gcc -S -O1 -emit-llvm -o - ambika.c
> ambika.c: In function ‘main’:
> ambika.c:7: warning: incompatible implicit declaration of built-in
> function ‘printf’
> ; ModuleID = 'ambika.c'
> target datalayout =
>
"e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
>
> target triple = "x86_64-unknown-linux-gnu"
>
> @.str = private constant [9 x i8] c"%d,%d,%d\00", align 1 ;
<[9 x
> i8]*> [#uses=1]
>
> define i32 @main() nounwind {
> entry:
> %0 = tail call i32 (i8*, ...)* @printf(i8* getelementptr inbounds
> ([9 x i8]* @.str, i64 0, i64 0), i32 4, i32 4, i32 4) nounwind ;
<i32>
> [#uses=0]
> ret i32 0
> }
>
> declare i32 @printf(i8* nocapture, ...) nounwind
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