[IR] Support scalable vectors in ShuffleVectorInst::increasesLength

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.

Reviewed By: sdesmalen

Differential Revision: https://reviews.llvm.org/D92472

llvm/include/llvm/IR/Instructions.h

@@ -2081,8 +2081,9 @@ public:
   /// 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;
   }

llvm/unittests/IR/InstructionsTest.cpp

@@ -1083,7 +1083,19 @@ TEST(InstructionsTest, ShuffleMaskQueries) {
                             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) {