[RISCV] Don't enable loop vectorizer interleaving if the V extension is scalable

[liaolucy]

Summary

Possible scalable vectorization does not require unroll

[kito-cheng]

llvm/lib/Target/RISCV/RISCVSubtarget.h

226

useRVVForFixedLengthVectors() means we CAN use fixed vector but isn't means we CAN ONLY use fixed vector for vectorizer, so I think that would be vectorizer issue rather than backend's issue.

[liaolucy]

llvm/lib/Target/RISCV/RISCVSubtarget.h

226

Thanks kito, any good modification suggestions?

llvm/lib/Target/RISCV/RISCVSubtarget.h

 //===-- RISCVSubtarget.h - Define Subtarget for the RISCV -------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
public:
   bool hasVInstructionsF16() const { return HasStdExtZve32f && HasStdExtZfh; }
   // FIXME: Consider Zfinx in the future
   bool hasVInstructionsF32() const { return HasStdExtZve32f && HasStdExtF; }
   // FIXME: Consider Zdinx in the future
   bool hasVInstructionsF64() const { return HasStdExtZve64d && HasStdExtD; }
   // F16 and F64 both require F32.
   bool hasVInstructionsAnyF() const { return hasVInstructionsF32(); }
   unsigned getMaxInterleaveFactor() const {
-    return hasVInstructions() ? MaxInterleaveFactor : 1;
+    return useRVVForFixedLengthVectors() ? MaxInterleaveFactor : 1;
   }
 
 protected:
   // GlobalISel related APIs.
   std::unique_ptr<CallLowering> CallLoweringInfo;
   std::unique_ptr<InstructionSelector> InstSelector;
   std::unique_ptr<LegalizerInfo> Legalizer;
   std::unique_ptr<RegisterBankInfo> RegBankInfo;