Don't fold (select C, (gep Ptr, Idx), Ptr) if C is vector but Idx is scalar

The folding rule (select C, (gep Ptr, Idx), Ptr) -> (gep Ptr, (select C,
Idx, 0)) creates a malformed SELECT IR if C is a vector while Idx is scalar.

  SELECT VecC, ScalarIdx, 0

We could splat Idx to a vector but it defeats the purpose of
optimisation. Don't apply the folding rule in this case.

This fixes a regression from commit d561b6f.

Author: kongy

llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp

@@ -3004,8 +3004,10 @@ Instruction *InstCombinerImpl::visitSelectInst(SelectInst &SI) {
     if (Gep->getNumOperands() != 2 || Gep->getPointerOperand() != Base ||
         !Gep->hasOneUse())
       return nullptr;
-    Type *ElementType = Gep->getResultElementType();
     Value *Idx = Gep->getOperand(1);
+    if (isa<VectorType>(CondVal->getType()) && !isa<VectorType>(Idx->getType()))
+      return nullptr;
+    Type *ElementType = Gep->getResultElementType();
     Value *NewT = Idx;
     Value *NewF = Constant::getNullValue(Idx->getType());
     if (Swap)

llvm/test/Transforms/InstCombine/select-gep.ll

@@ -244,3 +244,16 @@ define i32* @test6(i32* %p, i64 %x, i64 %y) {
   ret i32* %sel
 }
 declare void @use_i32p(i32*)
+
+; We cannot create a select-with-idx with a vector condition but scalar idx.
+
+define <2 x i64*> @test7(<2 x i64*> %p1, i64 %idx, <2 x i1> %cc) {
+; CHECK-LABEL: @test7(
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr i64, <2 x i64*> [[P1:%.*]], i64 [[IDX]]
+; CHECK-NEXT:    [[SELECT:%.*]] = select <2 x i1> [[CC:%.*]], <2 x i64*> [[P1:%.*]], <2 x i64*> [[GEP]]
+; CHECK-NEXT:    ret <2 x i64*> [[SELECT]]
+;
+  %gep = getelementptr i64, <2 x i64*> %p1, i64 %idx
+  %select = select <2 x i1> %cc, <2 x i64*> %p1, <2 x i64*> %gep
+  ret <2 x i64*> %select
+}