RFR: fixing bug in null checks generation

[Vicente Romero]

Javac is generating erroneous null checks for code like, test case provided by Jan:


public class Main {
    public String g() {
        return Other.str = "";
    }
}
class Other {
    public static String! str = "";
}

so there is no point in generating null checks on the left side of an assignment statement. So the proposal is to use a switch to indicate when null checks shouldn't be generated.

TIA

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Commit messages:
 - fixing bug in null checks generation

Changes: https://git.openjdk.org/valhalla/pull/1972/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1972&range=00
  Stats: 65 lines in 1 file changed: 39 ins; 1 del; 25 mod
  Patch: https://git.openjdk.org/valhalla/pull/1972.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1972/head:pull/1972

PR: https://git.openjdk.org/valhalla/pull/1972