8371162: Compiler warns about implicit cast from long to int in shift operation

[archiecobbs]

Consider code like this:

int x = 1;
x <<= 1L;

The compiler currently emits this warning:

warning: [lossy-conversions] implicit cast from long to int in compound assignment is possibly lossy
        x <<= 1L;
              ^

By definition, bit shift operations only use the bottom 5 or 6 bits of the specified shift amount (in this example, 1L), and the JLS does not require the shift amount to be any specific integral type, only that that it be some integral type. So as long all but the bottom 5 or 6 bits are zero, there is no loss of information and the warning is inappropriate.

The case where the bottom 5 or 6 bits are not all zero is addressed separately in JDK-5038439.

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Issue

• JDK-8371162: Compiler warns about implicit cast from long to int in shift operation (Bug - P4)(⚠️ The fixVersion in this issue is [27] but the fixVersion in .jcheck/conf is 26, a new backport will be created when this pr is integrated.)

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