[RISCV][IA] Rework VL for strided LD/ST optimization [nfc] (llvm#150525)

I'd originally written this creating a new VL, but realized it was
probably cleaner to be explicit about the truncation which is happening.
As these VLs are all constants (since these two codepaths see fixed
vectors) this should result in identical constants being created.

Author: preames

llvm/lib/Target/RISCV/RISCVInterleavedAccess.cpp

@@ -224,10 +224,10 @@ bool RISCVTargetLowering::lowerInterleavedLoad(
     Value *Stride = ConstantInt::get(XLenTy, Factor * ScalarSizeInBytes);
     Value *Offset = ConstantInt::get(XLenTy, Indices[0] * ScalarSizeInBytes);
     Value *BasePtr = Builder.CreatePtrAdd(Ptr, Offset);
-    // Note: Same VL as above, but i32 not xlen due to signature of
-    // vp.strided.load
-    VL = Builder.CreateElementCount(Builder.getInt32Ty(),
-                                    VTy->getElementCount());
+    // For rv64, need to truncate i64 to i32 to match signature.  As VL is at most
+    // the number of active lanes (which is bounded by i32) this is safe.
+    VL = Builder.CreateTrunc(VL, Builder.getInt32Ty());
+
     CallInst *CI =
         Builder.CreateIntrinsic(Intrinsic::experimental_vp_strided_load,
                                 {VTy, BasePtr->getType(), Stride->getType()},
@@ -302,10 +302,9 @@ bool RISCVTargetLowering::lowerInterleavedStore(Instruction *Store,
     Value *Stride = ConstantInt::get(XLenTy, Factor * ScalarSizeInBytes);
     Value *Offset = ConstantInt::get(XLenTy, Index * ScalarSizeInBytes);
     Value *BasePtr = Builder.CreatePtrAdd(Ptr, Offset);
-    // Note: Same VL as above, but i32 not xlen due to signature of
-    // vp.strided.store
-    VL = Builder.CreateElementCount(Builder.getInt32Ty(),
-                                    VTy->getElementCount());
+    // For rv64, need to truncate i64 to i32 to match signature.  As VL is at
+    // most the number of active lanes (which is bounded by i32) this is safe.
+    VL = Builder.CreateTrunc(VL, Builder.getInt32Ty());
 
     CallInst *CI =
         Builder.CreateIntrinsic(Intrinsic::experimental_vp_strided_store,