[SROA] Remove unnecessary IsStorePastEnd handling (NFCI)

Unlike the load case, stores past the end of the alloca are
removed by SROA as undefined behavior. As such, there is no need
to handle this case when rewriting stores.

Author: nikic

llvm/lib/Transforms/Scalar/SROA.cpp

@@ -2891,26 +2891,10 @@ class llvm::sroa::AllocaSliceRewriter
     if (IntTy && V->getType()->isIntegerTy())
       return rewriteIntegerStore(V, SI, AATags);
 
-    const bool IsStorePastEnd =
-        DL.getTypeStoreSize(V->getType()).getFixedValue() > SliceSize;
     StoreInst *NewSI;
     if (NewBeginOffset == NewAllocaBeginOffset &&
         NewEndOffset == NewAllocaEndOffset &&
-        (canConvertValue(DL, V->getType(), NewAllocaTy) ||
-         (IsStorePastEnd && NewAllocaTy->isIntegerTy() &&
-          V->getType()->isIntegerTy()))) {
-      // If this is an integer store past the end of slice (and thus the bytes
-      // past that point are irrelevant or this is unreachable), truncate the
-      // value prior to storing.
-      if (auto *VITy = dyn_cast<IntegerType>(V->getType()))
-        if (auto *AITy = dyn_cast<IntegerType>(NewAllocaTy))
-          if (VITy->getBitWidth() > AITy->getBitWidth()) {
-            if (DL.isBigEndian())
-              V = IRB.CreateLShr(V, VITy->getBitWidth() - AITy->getBitWidth(),
-                                 "endian_shift");
-            V = IRB.CreateTrunc(V, AITy, "load.trunc");
-          }
-
+        canConvertValue(DL, V->getType(), NewAllocaTy)) {
       V = convertValue(DL, IRB, V, NewAllocaTy);
       Value *NewPtr =
           getPtrToNewAI(SI.getPointerAddressSpace(), SI.isVolatile());