Disable Loop unrolling protmotion for Alloc

Disable Loop unrolling protmotion for Alloc

Author: lioujheyu

IGC/Compiler/GenTTI.cpp

@@ -318,8 +318,7 @@ void GenIntrinsicsTTIImpl::getUnrollingPreferences(Loop *L, ScalarEvolution &SE,
   //       It can potentially do some global cost estimations.
   const unsigned UnrollMaxCountForAlloca = IGC_GET_FLAG_VALUE(PromoteLoopUnrollwithAllocaCountThreshold);
   bool AllocaFound = false;
-  if (MaxTripCount && MaxTripCount <= UnrollMaxCountForAlloca &&
-      IGC_IS_FLAG_ENABLED(EnablePromoteLoopUnrollwithAlloca)) {
+  if (MaxTripCount && MaxTripCount <= UnrollMaxCountForAlloca ) {
     unsigned int ThresholdBoost = 0;
     for (auto BB : L->blocks()) {
       for (auto &I : *BB) {
@@ -363,7 +362,8 @@ void GenIntrinsicsTTIImpl::getUnrollingPreferences(Loop *L, ScalarEvolution &SE,
       UP.UpperBound = true;
       UP.Force = UnrollLoopForCodeSizeOnly ? false : true;
 
-      if (ctx->type != ShaderType::OPENCL_SHADER) {
+      if (IGC_IS_FLAG_ENABLED(EnablePromoteLoopUnrollwithAlloca) &&
+          ctx->type != ShaderType::OPENCL_SHADER) {
         UP.Threshold += ThresholdBoost;
         LLVM_DEBUG(dbgs() << "Increasing L:" << L->getName() << " threshold to " << UP.Threshold
                           << " due to Alloca accessed by:");

IGC/common/igc_flags.h

@@ -447,7 +447,7 @@ DECLARE_IGC_REGKEY(DWORD, SetLoopUnrollMaxPercentThresholdBoostForHighRegPressur
                    "The LLVM internal value is 400.",
                    false)
 DECLARE_IGC_REGKEY(
-    bool, EnablePromoteLoopUnrollwithAlloca, true,
+    bool, EnablePromoteLoopUnrollwithAlloca, false,
     "Loop cost estimation assumes Load/Store who accesses Alloca with index deductible to loop count having 0 cost. "
     "Disable this flag makes them always cost something as well as disables dynamic threshold increase based on the "
     "size of alloca and number of GEP to the alloca in the loop, leading to the loop less likely to be unrolled.",