ValueTracking: do not return nullptr in case non-const index is detected

In case a part of structure that didn't contain image was modified with dynamic
index, we could lose opportunity to track the value.
When we return nullptr, the BTI is set to 0 and we end up with wrong access. It
is better to continue searching, as no high-level API is allowed to access
images dynamically currently.

Author: PawelJurek

IGC/Compiler/Optimizer/ValueTracker.cpp

@@ -286,16 +286,7 @@ Value* ValueTracker::findAllocaValue(Value* V, const uint depth)
         if (auto* GEP = dyn_cast<GetElementPtrInst>(U))
         {
             if (!GEP->hasAllConstantIndices()) {
-                // We can continue, only if the non-const index was after our depth.
-                unsigned firstNonConstIndex = 0;
-                for (unsigned i = 0; i < GEP->getNumIndices(); ++i) {
-                    if (!isa<ConstantInt>(GEP->getOperand(i + 1))) {
-                        firstNonConstIndex = i;
-                        break;
-                    }
-                }
-                if (firstNonConstIndex < depth)
-                    return nullptr;
+                continue;
             }
 
             unsigned numIndices = GEP->getNumIndices();