Add control for branch swapping pass

Change-Id: I60ab20d834dac627186d3db8e12def82b3e0e55e

Author: fftzeng

IGC/Compiler/CISACodeGen/DriverInfo.hpp

@@ -86,7 +86,10 @@ class CDriverInfo
 
     /// We can safely ignore Nan
     virtual bool IgnoreNan() const { return false; }
-    
+
+    // Allow branch swapping for better Nan perf
+    virtual bool BranchSwapping() const { return false; }
+
     /// Allow propagation up-converstion of half if it can generate better code
     virtual bool AllowUnsafeHalf() const { return true; }
 

IGC/Compiler/CISACodeGen/ShaderCodeGen.cpp

@@ -565,7 +565,7 @@ inline void AddLegalizationPasses(CodeGenContext &ctx, IGCPassManager& mpm)
     mpm.add(new BreakConstantExpr());
     mpm.add(new Legalization(preserveNan));
 
-    if (IGC_IS_FLAG_DISABLED(DisableBranchSwaping))
+    if (IGC_IS_FLAG_DISABLED(DisableBranchSwaping) && ctx.m_DriverInfo.BranchSwapping())
     {
         mpm.add(createNanHandlingPass());
     }

IGC/common/igc_flags.def

@@ -88,7 +88,7 @@ DECLARE_IGC_REGKEY(bool, DisableMatchPow,               false, "Setting this to
 DECLARE_IGC_REGKEY(bool, DisableIRVerification,         false, "Setting this to 1/true adds a compiler switch to disable IGC IR verification.")
 DECLARE_IGC_REGKEY(bool, DisableLoopUnroll,             false, "Setting this to 1/true adds a compiler switch to disable loop unrolling.")
 DECLARE_IGC_REGKEY(bool, DisableRuntimeLoopUnrolling,   false, "Setting this to 1/true adds a compiler switch to disable runtime loop unrolling.")
-DECLARE_IGC_REGKEY(bool, DisableBranchSwaping,          true,  "Setting this to 1/true adds a compiler switch to disable branch NAN swapping.")
+DECLARE_IGC_REGKEY(bool, DisableBranchSwaping,          false, "Setting this to 1/true adds a compiler switch to disable branch NAN swapping.")
 DECLARE_IGC_REGKEY(DWORD,SetLoopUnrollThreshold,        0,     "Set the loop unroll threshold. Value 0 will use the default threshold.")
 DECLARE_IGC_REGKEY(DWORD,SetBranchSwapThreshold,        100,   "Set the branch swaping threshold.")
 DECLARE_IGC_REGKEY(debugString, LLVMCommandLine,        0,     "applies LLVM command line")