[SPIRV] fix build with clang and use PoisonValue instead of UndefValue

[iliya-diyachkov]

Summary

The patch fixes the backend build using clang (#57773). It also replaces UndefValue with PoisonValue in SPIRVRegularizer.cpp as requested by @nlopes.

[nlopes]

llvm/lib/Target/SPIRV/SPIRVRegularizer.cpp

241

This code seems to be implementing a splat of CI->getOperand(1) to a vector of type ArgoTy.
You can use IRBuilder's CreateVectorSplat() to simplify this code (https://llvm.org/doxygen/classllvm_1_1IRBuilderBase.html#a40ed7274ff11f079e5b5eae34c818c51).

[iliya-diyachkov]

llvm/lib/Target/SPIRV/SPIRVRegularizer.cpp

241

Thanks, Nuno. Yes it gives the same result as splat, but for now we'd prefer the backend to generate the same code as the SIPR-V translator does (inserting InsertElementInst and ShuffleVectorInst instructions). For instance (transcoding/OpMin.ll), it converts this call in LLVM IR

%call = tail call spir_func <2 x i32> @_Z3minDv2_ii(<2 x i32> <i32 1, i32 10>, i32 5) #2

to the following SPIR-V fragment:

          %8 = OpUndef %v2uint
         %14 = OpConstantComposite %v2uint %uint_1 %uint_10
...
         %10 = OpCompositeInsert %v2uint %uint_5 %8 0
         %11 = OpVectorShuffle %v2uint %10 %8 0 0
       %call = OpExtInst %v2uint %1 s_min %14 %11

so InsertElementInst and ShuffleVectorInst are required.

[iliya-diyachkov]

Add a comment.

llvm/lib/Target/SPIRV/SPIRVBuiltins.cpp

Type *ImageOpaqueType = StructType::getTypeByName(
       Context, "spirv.Image." + TypeParametersString.str());
   SPIRVType *TargetImageType =
       GR->getOrCreateSPIRVType(ImageOpaqueType, MIRBuilder);
   return GR->getOrCreateOpTypeSampledImage(TargetImageType, MIRBuilder);
 }
 
 namespace SPIRV {
 SPIRVType *lowerBuiltinType(const StructType *OpaqueType,
-                            AccessQualifier::AccessQualifier AccessQual,
+                            SPIRV::AccessQualifier::AccessQualifier AccessQual,
                             MachineIRBuilder &MIRBuilder,
                             SPIRVGlobalRegistry *GR) {
   assert(OpaqueType->hasName() &&
          "Structs representing builtin types must have a parsable name");
   unsigned NumStartingVRegs = MIRBuilder.getMRI()->getNumVirtRegs();
 
   const StringRef Name = OpaqueType->getName();
   LLVM_DEBUG(dbgs() << "Lowering builtin type: " << Name << "\n");

llvm/lib/Target/SPIRV/SPIRVRegularizer.cpp

CloneFunctionInto(NewF, OldF, VMap,
                       CloneFunctionChangeType::LocalChangesOnly, Returns);
     NewF->setAttributes(Attrs);
     Old2NewFuncs[OldF] = NewF;
   } else {
     NewF = Old2NewFuncs[OldF];
   }
   assert(NewF);
 
+  // This produces an instruction sequence that implements a splat of
+  // CI->getOperand(1) to a vector Arg0Ty. However, we use InsertElementInst
+  // and ShuffleVectorInst to generate the same code as the SPIR-V translator.
+  // For instance (transcoding/OpMin.ll), this call
+  //   call spir_func <2 x i32> @_Z3minDv2_ii(<2 x i32> <i32 1, i32 10>, i32 5)
+  // is translated to
+  //    %8 = OpUndef %v2uint
+  //   %14 = OpConstantComposite %v2uint %uint_1 %uint_10
+  //   ...
+  //   %10 = OpCompositeInsert %v2uint %uint_5 %8 0
+  //   %11 = OpVectorShuffle %v2uint %10 %8 0 0
+  // %call = OpExtInst %v2uint %1 s_min %14 %11
   auto ConstInt = ConstantInt::get(IntegerType::get(CI->getContext(), 32), 0);
-  UndefValue *UndefVal = UndefValue::get(Arg0Ty);
+  PoisonValue *PVal = PoisonValue::get(Arg0Ty);
   Instruction *Inst =
-      InsertElementInst::Create(UndefVal, CI->getOperand(1), ConstInt, "", CI);
+      InsertElementInst::Create(PVal, CI->getOperand(1), ConstInt, "", CI);
   ElementCount VecElemCount = cast<VectorType>(Arg0Ty)->getElementCount();
   Constant *ConstVec = ConstantVector::getSplat(VecElemCount, ConstInt);
-  Value *NewVec = new ShuffleVectorInst(Inst, UndefVal, ConstVec, "", CI);
+  Value *NewVec = new ShuffleVectorInst(Inst, PVal, ConstVec, "", CI);
   CI->setOperand(1, NewVec);
   CI->replaceUsesOfWith(OldF, NewF);
   CI->mutateFunctionType(NewF->getFunctionType());
 }
 
 bool SPIRVRegularizer::runOnFunction(Function &F) {
   runLowerConstExpr(F);
   visit(F);