[VPlan] Use VPInstructionWithType for casts in VPlan0. (NFC)

Use VPInstructionWithType for casts in VPlan0, to enable additional
analysis/transforms on VPlan0, and more accurate modeling in VPlan0.

Author: fhahn

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -8157,9 +8157,10 @@ VPRecipeBase *VPRecipeBuilder::tryToCreateWidenRecipe(VPSingleDefRecipe *R,
     return new VPWidenSelectRecipe(*cast<SelectInst>(Instr), R->operands());
 
   if (Instruction::isCast(VPI->getOpcode())) {
+    auto *CastR = cast<VPInstructionWithType>(R);
     auto *CI = cast<CastInst>(Instr);
     return new VPWidenCastRecipe(CI->getOpcode(), VPI->getOperand(0),
-                                 CI->getType(), *CI);
+                                 CastR->getResultType(), *CI);
   }
 
   return tryToWiden(VPI);

llvm/lib/Transforms/Vectorize/VPlanConstruction.cpp

@@ -20,6 +20,7 @@
 #include "llvm/Analysis/LoopInfo.h"
 #include "llvm/Analysis/LoopIterator.h"
 #include "llvm/Analysis/ScalarEvolution.h"
+#include "llvm/IR/InstrTypes.h"
 #include "llvm/IR/MDBuilder.h"
 
 #define DEBUG_TYPE "vplan"
@@ -233,10 +234,15 @@ void PlainCFGBuilder::createVPInstructionsForVPBB(VPBasicBlock *VPBB,
       for (Value *Op : Inst->operands())
         VPOperands.push_back(getOrCreateVPOperand(Op));
 
-      // Build VPInstruction for any arbitrary Instruction without specific
-      // representation in VPlan.
-      NewR = cast<VPInstruction>(
-          VPIRBuilder.createNaryOp(Inst->getOpcode(), VPOperands, Inst));
+      if (auto *CI = dyn_cast<CastInst>(Inst)) {
+        NewR = VPIRBuilder.createScalarCast(CI->getOpcode(), VPOperands[0],
+                                            CI->getType(), CI->getDebugLoc());
+        NewR->setUnderlyingValue(CI);
+      } else {
+        // Build VPInstruction for any arbitrary Instruction without specific
+        // representation in VPlan.
+        NewR = VPIRBuilder.createNaryOp(Inst->getOpcode(), VPOperands, Inst);
+      }
     }
 
     IRDef2VPValue[Inst] = NewR;