[LLVMdev] difference between alias set tracker and alias analysis evaluator

[Amr Yehia]

Hi all,

I have a problem with alias aliasing results returned by the alias set 
tracker and the alias analysis evaluator.

so i call opt tool to run my module with the following options 
"-anders-aa -aa-eval -print-alias-sets -print-all-alias-modref-info"
i use 2 classes to print alias analysis, the AliasSetTracket and 
AliasAnalysisEvaluator.
but they give different results.

here is a sample program:
int main(){
    int a[5];
    struct {
            char    id[10];
            int     line;
    } sym;
    sym.line =a[1] + 10;
    a[3] = 3;
    sym.id[5] = a[3];
    return 0;
}

and here is the ll file
define i32 @main() nounwind {
entry:
    %retval = alloca i32        ; <i32*> [#uses=2]
    %sym = alloca %struct..0anon        ; <%struct..0anon*> [#uses=2]
    %a = alloca [5 x i32]        ; <[5 x i32]*> [#uses=3]
    %0 = alloca i32        ; <i32*> [#uses=2]
    %"alloca point" = bitcast i32 0 to i32        ; <i32> [#uses=0]
    %1 = getelementptr [5 x i32]* %a, i32 0, i64 1        ; <i32*> [#uses=1]
    %2 = load i32* %1, align 4        ; <i32> [#uses=1]
    %3 = add i32 %2, 10        ; <i32> [#uses=1]
    %4 = getelementptr %struct..0anon* %sym, i32 0, i32 1        ; 
<i32*> [#uses=1]
    store i32 %3, i32* %4, align 4
    %5 = getelementptr [5 x i32]* %a, i32 0, i64 3        ; <i32*> [#uses=1]
    store i32 3, i32* %5, align 4
    %6 = getelementptr [5 x i32]* %a, i32 0, i64 3        ; <i32*> [#uses=1]
    %7 = load i32* %6, align 4        ; <i32> [#uses=1]
    %8 = trunc i32 %7 to i8        ; <i8> [#uses=1]
    %9 = getelementptr %struct..0anon* %sym, i32 0, i32 0        ; <[10 
x i8]*> [#uses=1]
    %10 = getelementptr [10 x i8]* %9, i32 0, i64 5        ; <i8*> [#uses=1]
    store i8 %8, i8* %10, align 1
    store i32 0, i32* %0, align 4
    %11 = load i32* %0, align 4        ; <i32> [#uses=1]
    store i32 %11, i32* %retval, align 4
    br label %return

return:        ; preds = %entry
    %retval1 = load i32* %retval        ; <i32> [#uses=1]
    ret i32 %retval1
}

the AliasSetTracker gives the following result:
Alias Set Tracker: 6 alias sets for 7 pointer values.
  AliasSet[0x2ce5d30,1] must alias, Ref       Pointers: (i32* %1, 4)
  AliasSet[0x2ce5ab0,1] must alias, Mod       Pointers: (i32* %4, 4)
  AliasSet[0x2ce59c0,2] must alias, Mod/Ref   Pointers: (i32* %5, 4), 
(i32* %6, 4)
  AliasSet[0x2ce5910,1] must alias, Mod       Pointers: (i8* %10, 1)
  AliasSet[0x2ce5820,1] must alias, Mod/Ref   Pointers: (i32* %0, 4)
  AliasSet[0x2ce4f00,1] must alias, Mod/Ref   Pointers: (i32* %retval, 4)

the alias analysis evaluator gives the following results (i removed all 
the NoAlias results)
  MayAlias:    [5 x i32]* %a, i32* %1
  MayAlias:    %struct..0anon* %sym, i32* %4
  MayAlias:    [5 x i32]* %a, i32* %5
  MayAlias:    [5 x i32]* %a, i32* %6
  MustAlias:    i32* %5, i32* %6
  MustAlias:    %struct..0anon* %sym, [10 x i8]* %9
  MayAlias:    %struct..0anon* %sym, i8* %10
  MayAlias:    [10 x i8]* %9, i8* %10

so my questions finally are:
- why is there is a difference between the 2 results,
- how can i get the alias set tracker to give me all the aliasing 
results returned by alias analysis evaluator


thank you