Improve unroll heuristics for 1-BB loops

Double LoopUnrollThreshold for 1-BB outermost loops in small OCL kernels
without Call instructions.

Author: agrabezh

IGC/Compiler/GenTTI.cpp

@@ -539,6 +539,28 @@ void GenIntrinsicsTTIImpl::getUnrollingPreferences(Loop *L, ScalarEvolution &SE,
     return;
   }
 
+  auto hasCall = [](BasicBlock *BB) {
+    for (auto BI = BB->begin(), BE = BB->end(); BI != BE; ++BI)
+      if (isa<CallInst>(&*BI))
+        return true;
+    return false;
+  };
+
+  // Double LoopUnrollThreshold for 1-BB outermost loops in small OCL kernels
+  // without Call instructions, since we expect better optimization
+  // when these loops are fully unrolled.
+  if (ctx->type == ShaderType::OPENCL_SHADER && !hasCall(L->getHeader()) && L->getHeader()->getParent()->size() < 5) {
+    if (!L->getParentLoop() && TripCount != 0 && TripCount < 256) {
+      UP.Count = TripCount;
+      UP.MaxCount = UP.Count;
+      UP.Threshold = LoopUnrollThreshold * 2;
+      UP.Runtime = false;
+      UP.Partial = false;
+      UP.Force = true;
+      return;
+    }
+  }
+
   for (I = loopBlock->begin(); I != loopBlock->end(); I++) {
     if (const auto pIntrinsic = llvm::dyn_cast<llvm::GenIntrinsicInst>(I)) {
       if (isSendMessage(pIntrinsic)) {