Do not lower constant predicates

During predicate lowering we unbale, create new instructions and bale
again. But in a case of constant input, instead of instruction creation
constants are just folded. Such predicates should not be lowered - they
are represented as SETP

Author: mshelego

IGC/VectorCompiler/lib/GenXCodeGen/GenXPredRegionLowering.cpp

@@ -218,9 +218,11 @@ void GenXPredRegionLowering::processWrPredRegionBales() {
 void GenXPredRegionLowering::processWrPredRegion(Instruction &WrPredRegion) {
   IGC_ASSERT(vc::getAnyIntrinsicID(&WrPredRegion) ==
              GenXIntrinsic::genx_wrpredregion);
-  IRBuilder<> IRB(&WrPredRegion);
-
   Value *NewPred = WrPredRegion.getOperand(PredRegion::NewValueOperandNum);
+  // If wrpred has a constant input, it will be represented as SETP in vISA
+  if (isa<Constant>(NewPred))
+    return;
+  IRBuilder<> IRB(&WrPredRegion);
   Value *Sel = createSelect(*NewPred, IRB);
   NewPred = createPredWithICmp(*Sel, IRB);
 

IGC/VectorCompiler/test/PredRegionLowering/basic.ll

@@ -47,4 +47,12 @@ define spir_func void @test_rd_and_wrpredregion_bale(<32 x i1> %pred, <32 x i1>
 ; CHECK: %[[wrpr:.*]] = call <32 x i1> @llvm.genx.wrpredregion.v32i1.v16i1(<32 x i1> %pred2, <16 x i1> %[[cmp]], i32 16)
 }
 
+; CHECK-LABEL: test_const_wrpredregion
+; CHECK-NOT: select
+; CHECK-NOT: icmp
+define spir_func void @test_const_wrpredregion(<32 x i1> %pred) #0 {
+  %pred.wrpr = call <32 x i1> @llvm.genx.wrpredregion.v32i1.v16i1(<32 x i1> %pred, <16 x i1> <i1 true, i1 false, i1 true, i1 false, i1 true, i1 false, i1 true, i1 false, i1 true, i1 false, i1 true, i1 false, i1 true, i1 false, i1 true, i1 false>, i32 16)
+  ret void
+}
+
 attributes #0 = { "CMStackCall" }