[RISCV] Use the store value's VT as the MemoryVT after combining riscv.masked.strided.store (#89874)

According to `RISCVTargetLowering::getTgtMemIntrinsic`, the MemoryVT
is the scalar element VT for strided store and the MemoryVT is the
same as the store value's VT for unit-stride store.

After combining `riscv.masked.strided.store` to `masked.store`, we
just use the scalar element VT to construct `masked.store`, which is
wrong.

With wrong MemoryVT, the DAGCombiner will combine `trunc+masked.store`
to truncated `masked.store` because `TLI.canCombineTruncStore` returns
true.

So, we should use the store value's VT as the MemoryVT.

This fixes #89833.

Author: wangpc-pp

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

@@ -16832,7 +16832,7 @@ SDValue RISCVTargetLowering::PerformDAGCombine(SDNode *N,
           StrideC && StrideC->getZExtValue() == ElementSize)
         return DAG.getMaskedStore(Store->getChain(), DL, Value, Base,
                                   DAG.getUNDEF(XLenVT), Mask,
-                                  Store->getMemoryVT(), Store->getMemOperand(),
+                                  Value.getValueType(), Store->getMemOperand(),
                                   ISD::UNINDEXED, false);
       return SDValue();
     }

llvm/test/CodeGen/RISCV/pr89833.ll

@@ -0,0 +1,16 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc < %s -mtriple=riscv64 -mattr=+v | FileCheck %s
+
+declare void @llvm.riscv.masked.strided.store.nxv16i8.p0.i64(<vscale x 16 x i8>, ptr, i64, <vscale x 16 x i1>)
+
+define void @test(<vscale x 16 x i16> %value, <vscale x 16 x i1> %mask) {
+; CHECK-LABEL: test:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    vsetvli a0, zero, e8, m2, ta, ma
+; CHECK-NEXT:    vnsrl.wi v12, v8, 0
+; CHECK-NEXT:    vse8.v v12, (zero), v0.t
+; CHECK-NEXT:    ret
+  %trunc = trunc <vscale x 16 x i16> %value to <vscale x 16 x i8>
+  call void @llvm.riscv.masked.strided.store.nxv16i8.p0.i64(<vscale x 16 x i8> %trunc, ptr null, i64 1, <vscale x 16 x i1> %mask)
+  ret void
+}