RFR: 5038439: Warning message for literal shift amounts outside the canonical domain
Archie Cobbs
acobbs at openjdk.org
Tue Oct 7 19:40:35 UTC 2025
When bit shifting an `int` or `long` value by an amount `X`, all but the last 5 or 6 (respectively) bits of `X` are ignored.
This can create a trap for the unwary, as in this example:
public long readLongBigEndian(byte[] buf, int offset) {
return ((buf[offset + 0] & 0xff) << 56) // BUG HERE
| ((buf[offset + 1] & 0xff) << 48) // BUG HERE
| ((buf[offset + 2] & 0xff) << 40) // BUG HERE
| ((buf[offset + 3] & 0xff) << 32) // BUG HERE
| ((buf[offset + 4] & 0xff) << 24)
| ((buf[offset + 5] & 0xff) << 16)
| ((buf[offset + 6] & 0xff) << 8)
| ((buf[offset + 7] & 0xff);
}
This PR adds a new warning when the compiler detects an out-of-range bit shift, i.e., an `int` bit shift not in the range `[0...31]` or a `long` bit shift not in the range `[0...63]`.
-------------
Commit messages:
- Merge branch 'master' into JDK-5038439 to fix conflict.
- Add "long" as a supported message parameter type.
- Use "bit(s)" instead of "bits" where value could be 1.
- Merge branch 'master' into JDK-5038439
- Sprinkle more variety into the regression test.
- Minor diff cleanup.
- Update "lossy-conversions" description in compiler module Javadoc.
- Warn for bit shifts using an out-of-range shift amount.
Changes: https://git.openjdk.org/jdk/pull/27102/files
Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27102&range=00
Issue: https://bugs.openjdk.org/browse/JDK-5038439
Stats: 194 lines in 14 files changed: 184 ins; 0 del; 10 mod
Patch: https://git.openjdk.org/jdk/pull/27102.diff
Fetch: git fetch https://git.openjdk.org/jdk.git pull/27102/head:pull/27102
PR: https://git.openjdk.org/jdk/pull/27102
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