[GlobalOpt] Add test for PR39751 (NFC)

This has been fixed by D114889, as noted in the comments.

llvm/test/Transforms/GlobalOpt/pr39751.ll

@@ -0,0 +1,20 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --check-globals
+; RUN: opt -S -globalopt < %s | FileCheck %s
+
+; Check that we don't crash on vector GEP indices.
+
+@a = internal global [2 x i16] zeroinitializer, align 1
+
+;.
+; CHECK: @[[A:[a-zA-Z0-9_$"\\.-]+]] = internal unnamed_addr global [2 x i16] zeroinitializer, align 1
+;.
+define void @f1() {
+; CHECK-LABEL: @f1(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds [2 x i16], [2 x i16]* @a, i32 0, <2 x i32> <i32 0, i32 1>
+; CHECK-NEXT:    ret void
+;
+entry:
+  %gep = getelementptr inbounds [2 x i16], [2 x i16]* @a, i32 0, <2 x i32> <i32 0, i32 1>
+  ret void
+}