[GVN] Add test for capture via vector GEP (NFC)

Reported at:
#69931 (comment)

Author: nikic

llvm/test/Transforms/GVN/captured-before.ll

@@ -132,3 +132,21 @@ loop:
   call void @use(i32 %v) memory(none)
   br label %loop
 }
+
+; FIXME: This is a miscompile.
+define i32 @test_splat_gep_capture(<1 x i32> %index) {
+; CHECK-LABEL: define i32 @test_splat_gep_capture(
+; CHECK-SAME: <1 x i32> [[INDEX:%.*]]) {
+; CHECK-NEXT:    [[A:%.*]] = alloca i32, align 4
+; CHECK-NEXT:    store i32 123, ptr [[A]], align 4
+; CHECK-NEXT:    [[PTRS:%.*]] = getelementptr inbounds i32, ptr [[A]], <1 x i32> [[INDEX]]
+; CHECK-NEXT:    call void @some_call(<1 x ptr> [[PTRS]])
+; CHECK-NEXT:    ret i32 123
+;
+  %a = alloca i32
+  store i32 123, ptr %a
+  %ptrs = getelementptr inbounds i32, ptr %a, <1 x i32> %index
+  call void @some_call(<1 x ptr> %ptrs)
+  %reload = load i32, ptr %a
+  ret i32 %reload
+}