[VPlan] Support extends and truncs in getSCEVExprForVPValue. (NFCI)

Handle extends and truncates in getSCEVExprForVPValue. This enables
computing SCEVs in more cases in the VPlan-based cost-model, but should
compute the matching costs in all cases.

Author: fhahn

llvm/lib/Transforms/Vectorize/VPlanUtils.cpp

@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "VPlanUtils.h"
+#include "VPlanAnalysis.h"
 #include "VPlanCFG.h"
 #include "VPlanDominatorTree.h"
 #include "VPlanPatternMatch.h"
@@ -116,6 +117,27 @@ const SCEV *vputils::getSCEVExprForVPValue(const VPValue *V,
     return CreateSCEV({LHSVal, RHSVal}, [&](ArrayRef<const SCEV *> Ops) {
       return SE.getMinusSCEV(Ops[0], Ops[1], SCEV::FlagAnyWrap, 0);
     });
+  if (match(V, m_Trunc(m_VPValue(LHSVal)))) {
+    const VPlan *Plan = V->getDefiningRecipe()->getParent()->getPlan();
+    Type *DestTy = VPTypeAnalysis(*Plan).inferScalarType(V);
+    return CreateSCEV({LHSVal}, [&](ArrayRef<const SCEV *> Ops) {
+      return SE.getTruncateExpr(Ops[0], DestTy);
+    });
+  }
+  if (match(V, m_ZExt(m_VPValue(LHSVal)))) {
+    const VPlan *Plan = V->getDefiningRecipe()->getParent()->getPlan();
+    Type *DestTy = VPTypeAnalysis(*Plan).inferScalarType(V);
+    return CreateSCEV({LHSVal}, [&](ArrayRef<const SCEV *> Ops) {
+      return SE.getZeroExtendExpr(Ops[0], DestTy);
+    });
+  }
+  if (match(V, m_SExt(m_VPValue(LHSVal)))) {
+    const VPlan *Plan = V->getDefiningRecipe()->getParent()->getPlan();
+    Type *DestTy = VPTypeAnalysis(*Plan).inferScalarType(V);
+    return CreateSCEV({LHSVal}, [&](ArrayRef<const SCEV *> Ops) {
+      return SE.getSignExtendExpr(Ops[0], DestTy);
+    });
+  }
 
   // TODO: Support constructing SCEVs for more recipes as needed.
   const VPRecipeBase *DefR = V->getDefiningRecipe();