[IR] Support scalable vectors in ShuffleVectorInst::increasesLength

[c-rhodes]

Summary

Since the length of the llvm::SmallVector shufflemask is related to the
minimum number of elements in a scalable vector, it is fine to just get
the Min field of the ElementCount. This is already done for the similar
function changesLength, tests have been added for both.

[sdesmalen]

LGTM

llvm/unittests/IR/InstructionsTest.cpp

1095

Nothing to change in this patch, but I just thought this interface had been removed so that it would take an ArrayRef instead of a Constant?

[c-rhodes]

llvm/unittests/IR/InstructionsTest.cpp

1095

Nothing to change in this patch, but I just thought this interface had been removed so that it would take an ArrayRef instead of a Constant?

There's two interfaces where Mask can be either an llvm::Value or ArrayRef<int>, I think most of these tests are using the former interface since they pass an llvm::Constant

llvm/include/llvm/IR/Instructions.h

bool changesLength() const {
     unsigned NumMaskElts = ShuffleMask.size();
     return NumSourceElts != NumMaskElts;
   }
 
   /// Return true if this shuffle returns a vector with a greater number of
   /// elements than its source vectors.
   /// Example: shufflevector <2 x n> A, <2 x n> B, <1,2,3>
   bool increasesLength() const {
-    unsigned NumSourceElts =
-        cast<FixedVectorType>(Op<0>()->getType())->getNumElements();
+    unsigned NumSourceElts = cast<VectorType>(Op<0>()->getType())
+                                 ->getElementCount()
+                                 .getKnownMinValue();
     unsigned NumMaskElts = ShuffleMask.size();
     return NumSourceElts < NumMaskElts;
   }
 
   /// Return true if this shuffle mask chooses elements from exactly one source
   /// vector.
   /// Example: <7,5,undef,7>
   /// This assumes that vector operands are the same length as the mask.

llvm/unittests/IR/InstructionsTest.cpp

TEST(InstructionsTest, ShuffleMaskQueries) {
   // subvector.
   Type *VScaleV4Int32Ty = ScalableVectorType::get(Int32Ty, 4);
   ShuffleVectorInst *Id13 =
       new ShuffleVectorInst(Constant::getAllOnesValue(VScaleV4Int32Ty),
                             UndefValue::get(VScaleV4Int32Ty),
                             Constant::getNullValue(VScaleV4Int32Ty));
   int Index = 0;
   EXPECT_FALSE(Id13->isExtractSubvectorMask(Index));
+  EXPECT_FALSE(Id13->changesLength());
+  EXPECT_FALSE(Id13->increasesLength());
   delete Id13;
+
+  // Result has twice as many operands.
+  Type *VScaleV2Int32Ty = ScalableVectorType::get(Int32Ty, 2);
+  ShuffleVectorInst *Id14 =
+      new ShuffleVectorInst(Constant::getAllOnesValue(VScaleV2Int32Ty),
+                            UndefValue::get(VScaleV2Int32Ty),
+                            Constant::getNullValue(VScaleV4Int32Ty));
+  EXPECT_TRUE(Id14->changesLength());
+  EXPECT_TRUE(Id14->increasesLength());
+  delete Id14;
 }
 
 TEST(InstructionsTest, GetSplat) {
   // Create the elements for various constant vectors.
   LLVMContext Ctx;
   Type *Int32Ty = Type::getInt32Ty(Ctx);
   Constant *CU = UndefValue::get(Int32Ty);
   Constant *C0 = ConstantInt::get(Int32Ty, 0);