[IR] Bail out for scalable vectors in ShuffleVectorInst::isConcat

[c-rhodes]

Summary

Shuffle mask for concat can't be expressed for scalable vectors, so we
should bail out. A test has been added that previously crashed, also
tested isIdentityWithPadding and isIdentityWithExtract where we already
bail out.

[sdesmalen]

LGTM, a vector concat cannot be expressed for with shufflevector for scalable vectors.

llvm/lib/IR/Instructions.cpp

 }
 
 bool ShuffleVectorInst::isConcat() const {
   // Vector concatenation is differentiated from identity with padding.
   if (isa<UndefValue>(Op<0>()) || isa<UndefValue>(Op<1>()) ||
       isa<UndefValue>(Op<2>()))
     return false;
 
+  // FIXME: Not currently possible to express a shuffle mask for a scalable
+  // vector for this case.
+  if (isa<ScalableVectorType>(getType()))
+    return false;
+
   int NumOpElts = cast<FixedVectorType>(Op<0>()->getType())->getNumElements();
   int NumMaskElts = cast<FixedVectorType>(getType())->getNumElements();
   if (NumMaskElts != NumOpElts * 2)
     return false;
 
   // Use the mask length rather than the operands' vector lengths here. We
   // already know that the shuffle returns a vector twice as long as the inputs,
   // and neither of the inputs are undef vectors. If the mask picks consecutive

llvm/unittests/IR/InstructionsTest.cpp

TEST(InstructionsTest, ShuffleMaskQueries) {
   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;
+
+  // Not possible to express these masks for scalable vectors, make sure we
+  // don't crash.
+  ShuffleVectorInst *Id15 =
+      new ShuffleVectorInst(Constant::getAllOnesValue(VScaleV2Int32Ty),
+                            Constant::getNullValue(VScaleV2Int32Ty),
+                            Constant::getNullValue(VScaleV2Int32Ty));
+  EXPECT_FALSE(Id15->isIdentityWithPadding());
+  EXPECT_FALSE(Id15->isIdentityWithExtract());
+  EXPECT_FALSE(Id15->isConcat());
+  delete Id15;
 }
 
 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);