$y .= $y; # should warn once
EXPECT
Use of uninitialized value $x in concatenation (.) or string at - line 5.
-Use of uninitialized value $y in concatenation (.) or string at - line 6.
Use of uninitialized value $x in concatenation (.) or string at - line 6.
+Use of uninitialized value $y in concatenation (.) or string at - line 6.
Use of uninitialized value $y in concatenation (.) or string at - line 7.
Use of uninitialized value $y in concatenation (.) or string at - line 8.
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