[RISCV] remove useless code

[Miss_Grape]

Summary

when legality check for vectoring reduction， hasVInstructions() check be unneeded. RISCV can only loop vectorization with hasVInstructions()

[craig.topper]

LGTM, but please fix the description to use hasVInstructions instead of hasStdExtV since that's what's in the code.

[Miss_Grape]

In D125460#3509580, @craig.topper wrote:

LGTM, but please fix the description to use hasVInstructions instead of hasStdExtV since that's what's in the code.

Done.

[kito-cheng]

hasVInstructions() check be unneeded. RISCV can only loop vectorization with hasVInstructions()

For long term, I think that's not true, P/Packed-SIMD extensions should be able to apply loop vectorization too, but I am not opposite this getting merge, just remind we might need to add back in future.

[Miss_Grape]

In D125460#3510567, @kito-cheng wrote:

hasVInstructions() check be unneeded. RISCV can only loop vectorization with hasVInstructions()

For long term, I think that's not true, P/Packed-SIMD extensions should be able to apply loop vectorization too, but I am not opposite this getting merge, just remind we might need to add back in future.

I think we may need another feature to support P/Packed-SIMD extensions. We need to process this before legalization。

llvm/lib/Target/RISCV/RISCVTargetTransformInfo.h

public:
   TargetTransformInfo::VPLegalization
   getVPLegalizationStrategy(const VPIntrinsic &PI) const {
     using VPLegalization = TargetTransformInfo::VPLegalization;
     return VPLegalization(VPLegalization::Legal, VPLegalization::Legal);
   }
 
   bool isLegalToVectorizeReduction(const RecurrenceDescriptor &RdxDesc,
                                    ElementCount VF) const {
-    if (!ST->hasVInstructions())
-      return false;
-
     if (!VF.isScalable())
       return true;
 
     Type *Ty = RdxDesc.getRecurrenceType();
     if (!TLI->isLegalElementTypeForRVV(Ty))
       return false;
 
     switch (RdxDesc.getRecurrenceKind()) {