[llvm-dev] Finding Store Instructions that possibly affect load instruction or func call instruction

[sushant gokhale via llvm-dev]

Hi,

I want to track StoreInst that affect loadInst/CallInst.

e.g %1 = alloc i32
      store 10,%1
      foo(%1)      -------> %1 should take the value 10 (defined by store
ins)

I tried to use MemSSA for this but for situations I can't find these
correct dependencies possibly due to insufficient Alias information

e.g
Consider the C code:

__attribute__((noinline)) void foo(int i,int j){    printf("%d
%d",i,j);}int main(){    int j;    int k;    scanf("%d%d",&j,&k);
j+=10;    k-=3;    //func call to force the stores    foo(j,k);
//func call to force the loads    printf("%d %d",j,k);}


*MemSSA generated:*
define dso_local i32 @main() #2 {
  %1 = alloca i32, align 4
  %2 = alloca i32, align 4
  %3 = bitcast i32* %1 to i8*
; 1 = MemoryDef(liveOnEntry)
  call void @llvm.lifetime.start.p0i8(i64 4, i8* nonnull %3) #5
  %4 = bitcast i32* %2 to i8*
; 2 = MemoryDef(1)
  call void @llvm.lifetime.start.p0i8(i64 4, i8* nonnull %4) #5
  %5 = getelementptr inbounds [5 x i8], [5 x i8]* @.str.1, i64 0, i64 0
; 3 = MemoryDef(2)
  %6 = call i32 (i8*, ...) @__isoc99_scanf(i8* %5, i32* nonnull %1, i32*
nonnull %2)
; MemoryUse(3) MayAlias
  %7 = load i32, i32* %1, align 4, !tbaa !5
  %8 = add nsw i32 %7, 10
; 4 = MemoryDef(3)
  store i32 %8, i32* %1, align 4, !tbaa !5
; MemoryUse(3) MayAlias
  %9 = load i32, i32* %2, align 4, !tbaa !5
  %10 = add nsw i32 %9, -3
; 5 = MemoryDef(4)
  store i32 %10, i32* %2, align 4, !tbaa !5
; 6 = MemoryDef(5)
  call void @foo(i32 %8, i32 %10)
; MemoryUse(6) MayAlias
  %11 = load i32, i32* %1, align 4, !tbaa !5
; MemoryUse(6) MayAlias
  %12 = load i32, i32* %2, align 4, !tbaa !5
  %13 = getelementptr inbounds [6 x i8], [6 x i8]* @.str, i64 0, i64 0
; 7 = MemoryDef(6)
  %14 = call i32 (i8*, ...) @printf(i8* nonnull dereferenceable(1) %13, i32
%11, i32 %12)



Two  issues for me:
1. I am not able to track from where the values for %11 and %12 are coming.
There are coming from 2 store instructions before the foo call. But since
both loads   have defining ins as 6 = MemoryDef(5), I couldn't get these
stores.
The only way I could find them is traverse back using def chain created in
MemSSA

2. For function foo(), I can't trace from where parameter values are coming
from because MemSSA only gives 1 link up  i.e it tracks only 5 =
MemoryDef(4)and not the other store.  That is to say, its tracking only 1
parameter.

Is there any solution to this?

Regards
Sushant
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