problem in alias analysis

[kheradmand]

alias analysis code does not detect the alias in this code

        // store data to be written in output bin
        pthread_mutex_lock(OutMutex);
        //OutputBuffer[blockNum].buf = DecompressedData;
        ((outBuff*) vector_get(&OutputBuffer, blockNum))->buf = DecompressedData;
        //OutputBuffer[blockNum].bufSize = outSize;
        ((outBuff*) vector_get(&OutputBuffer, blockNum))->bufSize = outSize;
        pthread_mutex_unlock(OutMutex);

        #ifdef PBZIP_DEBUG
        //fprintf(stderr, " OutputBuffer[%d].buf = %x\n", blockNum, OutputBuffer[blockNum].buf);
        fprintf(stderr, " OutputBuffer[%d].buf = %x\n", blockNum, 
                ((outBuff*)vector_get(&OutputBuffer, blockNum))->buf);
        //fprintf(stderr, " OutputBuffer[%d].bufSize = %u\n", blockNum, OutputBuffer[blockNum].bufSize);
        fprintf(stderr, " OutputBuffer[%d].bufSize = %u\n", blockNum, 
                ((outBuff*)vector_get(&OutputBuffer, blockNum))->buf);
        #endif

So the is alias between the values that vector_get returns but alias analysis can not detect it.

[kheradmand]

in this simpler program

typedef struct vector_ {
  void** data;
  int size;
  int count;
} cvector;

static cvector OutputBuffer;





void *vector_get(cvector *v, int index)
{
  void* retVal = v->data[index];
  return retVal;
}



int main(){
    void* x = vector_get(&OutputBuffer, 10);
    void* y = vector_get(&OutputBuffer, 10);
    *(int*)y = 10;
    printf("%d",*(int*)x);
    return 0;
}

Also it does not detect the alias between x and y.

LLVM IR code is:

; Function Attrs: nounwind uwtable
define internal i8* @vector_get(%struct.vector_* %v, i32 %index) #0 {
entry:
  call void @llvm.dbg.value(metadata !{%struct.vector_* %v}, i64 0, metadata !23), !dbg !24
  call void @llvm.dbg.value(metadata !{i32 %index}, i64 0, metadata !25), !dbg !24
  %idxprom = sext i32 %index to i64, !dbg !26
  %data = getelementptr inbounds %struct.vector_* %v, i32 0, i32 0, !dbg !26
  %0 = load i8*** %data, align 8, !dbg !26
  %arrayidx = getelementptr inbounds i8** %0, i64 %idxprom, !dbg !26
  %1 = load i8** %arrayidx, align 8, !dbg !26
  call void @llvm.dbg.value(metadata !{i8* %1}, i64 0, metadata !27), !dbg !26
  ret i8* %1, !dbg !28
}

and during constraint collection of Andersen's we have this:

V7 OutputBuffer = &O6 OutputBuffer<mem>
O6 OutputBuffer<mem> = <null>
V18 vector_get:data = V17 vector_get:v
V19 vector_get:(  %0 = load i8*** %data, align 8, !dbg !26) = *V18 vector_get:data
V20 vector_get:arrayidx = V19 vector_get:(  %0 = load i8*** %data, align 8, !dbg !26)
V21 vector_get:(  %1 = load i8** %arrayidx, align 8, !dbg !26) = *V20 vector_get:arrayidx
R16 vector_get:retval = V21 vector_get:(  %1 = load i8** %arrayidx, align 8, !dbg !26)
V24 main:call = R16 vector_get:retval
V17 vector_get:v = V7 OutputBuffer
V25 main:call1 = R16 vector_get:retval
V17 vector_get:v = V7 OutputBuffer

and final point to graph:

[0] V28 main:call   --> 
V29 main:call1  --> same as V28 main:call

[kheradmand]

So this problem is actually is related to Issue #3
Consider this simpler code:

typedef struct vector_ {
  void* x;
} cvector;

static cvector OutputBuffer;

void *vector_get(cvector *v)
{
  void* retVal = v->x;
  return retVal;
}

int main(){

    void* x = vector_get(&OutputBuffer);
    void* y = vector_get(&OutputBuffer);
    *(int*)y = 10;
    printf("%d",*(int*)x);
    return 0;
}

so the constraints for this program:

V7 OutputBuffer = &O6 OutputBuffer<mem>
O6 OutputBuffer<mem> = <null>
F15 vector_get = &O10 vector_get<mem>
V18 vector_get:x = V17 vector_get:v
V19 vector_get:(  %0 = load i8** %x, align 8, !dbg !22) = *V18 vector_get:x
R16 vector_get:retval = V19 vector_get:(  %0 = load i8** %x, align 8, !dbg !22)
V22 main:call = R16 vector_get:retval
V17 vector_get:v = V7 OutputBuffer
V23 main:call1 = R16 vector_get:retval
V17 vector_get:v = V7 OutputBuffer

so since x = OutputBuffer, if we solve this constraints we get to call = OutputBuffer, hence call -> nothing
same about call1. So every thing (including the optimizer and constraint solver) is working correct, except this constraint that vector_get:x = V17 vector_get:v and this is because of Issue #3