Add check to detect OOB of Private/Function variables

[spencer-lunarg]

The following is currently not being caught in GPU-AV and should

const float myLut[40] = { /* array initializers... */ };
const int INVALID_LUT_INDEX = 63;

float func(int index) {
    return myLut[index];
}

void main() {
    /* lots of stuff */
    float thing = func(lutIndex); // lutIndex might be INVALID_LUT_INDEX 
}

[pmistryNV]

What is the impact on an application that turns on this feature that uses local variables heavily?
If every variable starts checking for OOB, will that not cause significant slowdown on GPU?

[spencer-lunarg]

(to start) it would only be for local variables that have an array and doing a dynamic index into them

It might be slow, would want to profile it (when there is an implementation to test)

we also have a "safe" and "unsafe" and could just do it on "safe" mode

also all of GPU-AV has this issue currently, everything you do in a shader could be invalid and this is a known concern

[pmistryNV]

Ok this is a limitation of this approach I guess and is probably not a scalable framework. Probably works well on a CPU, but on GPU branching for OOB is a problem

[spencer-lunarg]

@pmistryNV open for better ideas

[spencer-lunarg]

for the record, the GPU-AV code we do for Descriptor indexing OOB looks like

float func(int index) {
    float a = 0;
    if (index <= SIZE) {
         a = myLut[index];
    } else {
         ReportError();
    }
    return a;
}

for safe mode and for unsafe mode its just

float func(int index) {
    if (index > SIZE) {
         ReportError();
    }
    return myLut[index];
}

... welcome to debugging things on the GPU, again, VERY open to better solutions to GPU-AV