vISA will use dispatch simdsize from attribute instead of figuring

out by scanning all instructions.

Change-Id: I341c4ebc92c73d95211efceabcb765a5aaa82e69

Author: jgu222

visa/FlowGraph.cpp

@@ -6140,6 +6140,15 @@ void G4_Kernel::calculateSimdSize()
         return;
     }
 
+    // First, get simdsize from attribute (0 : not given)
+    simdSize = m_kernelAttrs->getIntKernelAttribute(Attributes::ATTR_SimdSize);
+    if (simdSize == 8 || simdSize == 16 || simdSize == 32)
+    {   // got it from attribute, done.
+        return;
+    }
+    // If not 0|8|16|32, wrong value from attribute.
+    assert(simdSize == 0 && "vISA: wrong value for SimdSize attribute");
+
     simdSize = 8;
 
     for (auto bb : fg)