[LoongArch] use TypeWidenVector for most illegal vector types (llvm#126456)

`TypeWidenVector` makes an illegal vector a larger one
e.g. in lsx
v2i32 -> v4i32
v4i16 -> v8i16
With this we can make good use of `vilvh`, `vilvl` instructions in
vector `sext`, `zext` in later pr.

Previous action is `TypePromoteInteger`, which replaces integer with a
larger one
e.g. in lsx
v2i32 -> v2i64
v4i16 -> v4i32

Author: tangaac

llvm/lib/Target/LoongArch/LoongArchISelLowering.cpp

@@ -6570,3 +6570,12 @@ bool LoongArchTargetLowering::shouldAlignPointerArgs(CallInst *CI,
 
   return true;
 }
+
+TargetLoweringBase::LegalizeTypeAction
+LoongArchTargetLowering::getPreferredVectorAction(MVT VT) const {
+  if (!VT.isScalableVector() && VT.getVectorNumElements() != 1 &&
+      VT.getVectorElementType() != MVT::i1)
+    return TypeWidenVector;
+
+  return TargetLoweringBase::getPreferredVectorAction(VT);
+}

llvm/lib/Target/LoongArch/LoongArchISelLowering.h

@@ -281,6 +281,7 @@ class LoongArchTargetLowering : public TargetLowering {
                               Align &PrefAlign) const override;
 
   bool isFPImmVLDILegal(const APFloat &Imm, EVT VT) const;
+  LegalizeTypeAction getPreferredVectorAction(MVT VT) const override;
 
 private:
   /// Target-specific function used to lower LoongArch calling conventions.