Add option to disable scalarization of phi nodes

Add option DisablePHIScalarization to skip phi nodes scalarization in
ScalarizeFunction pass

Author: admitric

IGC/Compiler/Optimizer/Scalarizer.cpp

@@ -383,7 +383,10 @@ void ScalarizeFunction::dispatchInstructionToScalarize(Instruction* I)
         scalarizeInstruction(dyn_cast<CastInst>(I));
         break;
     case Instruction::PHI:
-        scalarizeInstruction(dyn_cast<PHINode>(I));
+        if (IGC_IS_FLAG_DISABLED(DisablePHIScalarization))
+            scalarizeInstruction(dyn_cast<PHINode>(I));
+        else
+            recoverNonScalarizableInst(I);
         break;
     case Instruction::Select:
         scalarizeInstruction(dyn_cast<SelectInst>(I));

IGC/common/igc_flags.h

@@ -489,6 +489,7 @@ DECLARE_IGC_REGKEY(bool, DisableScalarAtomics,          false, "Disable the Scal
 DECLARE_IGC_REGKEY(bool, EnableScalarTypedAtomics,      true, "Enable the Scalar Typed Atomics optimization", false)
 DECLARE_IGC_REGKEY(bool, EnableVectorizer,              true, "Enable IGCVectorizer pass", false)
 DECLARE_IGC_REGKEY(bool, DisableOCLScalarizer,          false, "Disable ScalarizeFunction pass in OCL pipeline", true)
+DECLARE_IGC_REGKEY(bool, DisablePHIScalarization,       false, "Disable scalarization of PHINode instructions", true)
 DECLARE_IGC_REGKEY(bool, EnableSelectiveScalarizer,     false,  "enable selective scalarizer on GPGPU path", true)
 DECLARE_IGC_REGKEY(bool, HoistPSConstBufferValues,      true,  "Hoists up down converts for contant buffer accesses, so they an be vectorized more easily.", false)
 DECLARE_IGC_REGKEY(bool, EnableSingleVertexDispatch,    false, "Vertex Shader Single Patch Dispatch Regkey", false)

IGC/ocloc_tests/Options/disable_scalarize_option.ll

@@ -10,13 +10,14 @@
 
 ; RUN: llvm-as %s -o %t.bc
 ; RUN: ocloc compile -llvm_input -file %t.bc -device pvc -options " -ze-opt-large-register-file -igc_opts 'DisableOCLScalarizer=1,EnableVectorizer=0,PrintToConsole=1,PrintAfter=EmitPass'" 2>&1 | FileCheck %s --check-prefixes=CHECK
+; RUN: ocloc compile -llvm_input -file %t.bc -device pvc -options " -ze-opt-large-register-file -igc_opts 'DisablePHIScalarization=1,EnableVectorizer=0,PrintToConsole=1,PrintAfter=EmitPass'" 2>&1 | FileCheck %s --check-prefixes=CHECK
 
-; Check that scalarizer is disabled when DisableOCLScalarizer=1 is passed to IGC
+; Check that phi is not scalarized when DisableOCLScalarizer=1 or DisablePHIScalarization=1 is passed to IGC
 ; Disabling vectorizer as well in order to check that scalarizer is disabled and not vectorizer transformed the code
 
 ; CHECK-LABEL: @foo(
-; CHECK:       [[VEC_PHI:%.*]] = phi <8 x [[TYPE:[A-Za-z0-9]+]]> [ zeroinitializer, [[BB1:%.*]] ], [ [[V:%.*]], [[BB2:%.*]] ]
-; CHECK-NOT:   [[SCALAR_FLOAT_PHI:%.*]] = phi float [ [[ZERO:.*]], [[BB1:%.*]] ], [ [[TMP:%.*]], [[BB2:%.*]] ]
+; CHECK:       [[VEC_PHI:%.*]] = phi <8 x [[TYPE:[A-Za-z0-9]+]]>
+; CHECK-NOT:   [[SCALAR_FLOAT_PHI:%.*]] = phi float
 ; CHECK:       ret void