Set loop unroll threshold for high register pressure shaders via IGC flag

Also control the register pressure threshold used to limit the loop
unroll to smaller loops via IGC flag

Change-Id: Icef68a541145da98c1a04744dbeb3e1152cc5c7e

Author: srividyakarumuri

IGC/Compiler/GenTTI.cpp

@@ -133,19 +133,22 @@ namespace llvm {
             LoopUnrollThreshold = IGC_GET_FLAG_VALUE(SetLoopUnrollThreshold);
         }
         unsigned totalInstCountInShader = countTotalInstructions(L->getBlocks()[0]->getParent());
-        bool lowPressure = (this->ctx->m_tempCount < 64) && (totalInstCountInShader < LoopUnrollThreshold);
+        bool lowPressure = (this->ctx->m_tempCount < IGC_GET_FLAG_VALUE(SetRegisterPressureThresholdForLoopUnroll)) && (totalInstCountInShader < LoopUnrollThreshold);
         // For OCL shaders, do a two-step loop unrolling. The first
         // unrolling is simple and full, and the second runs after
         // LICM, which allows partial unrolling. Same for other APIs?
-        if (lowPressure || (ctx->type == ShaderType::OPENCL_SHADER) || (IGC_GET_FLAG_VALUE(SetLoopUnrollThreshold)))
+        if (lowPressure || (ctx->type == ShaderType::OPENCL_SHADER))
         {
             UP.Threshold = LoopUnrollThreshold;
             UP.PartialThreshold = LoopUnrollThreshold;
             UP.Partial = true;
         }
         else  // for high registry pressure shaders, limit the unrolling to small loops and only fully unroll
         {
-            UP.Threshold = 200;
+            if(IGC_GET_FLAG_VALUE(SetLoopUnrollThresholdForHighRegPressure) != 0)
+                UP.Threshold = IGC_GET_FLAG_VALUE(SetLoopUnrollThresholdForHighRegPressure);
+            else
+                UP.Threshold = 200;
         }
 
 #if LLVM_VERSION_MAJOR == 4

IGC/common/igc_flags.def

@@ -116,6 +116,8 @@ DECLARE_IGC_REGKEY(bool, DisableLoopUnroll,             false, "Setting this to
 DECLARE_IGC_REGKEY(bool, DisableRuntimeLoopUnrolling,   false, "Setting this to 1/true adds a compiler switch to disable runtime loop unrolling.", false)
 DECLARE_IGC_REGKEY(bool, DisableBranchSwaping,          false, "Setting this to 1/true adds a compiler switch to disable branch swapping.", false)
 DECLARE_IGC_REGKEY(DWORD,SetLoopUnrollThreshold,        0,     "Set the loop unroll threshold. Value 0 will use the default threshold.", false)
+DECLARE_IGC_REGKEY(DWORD,SetLoopUnrollThresholdForHighRegPressure,        0,     "Set the loop unroll threshold for shaders with high reg pressure. Value 0 will use the default threshold.", false)
+DECLARE_IGC_REGKEY(DWORD,SetRegisterPressureThresholdForLoopUnroll,       64,     "Set the register pressure threshold for limiting the loop unroll to smaller loops", false)
 DECLARE_IGC_REGKEY(DWORD,SetBranchSwapThreshold,        400,   "Set the branch swaping threshold.", false)
 DECLARE_IGC_REGKEY(debugString, LLVMCommandLine,        0,     "applies LLVM command line", false)
 DECLARE_IGC_REGKEY(bool, DisableDX9LowPrecision,        true,  "Disables HF in DX9.", false)