9bd9c628aa
We had previously fixed a bug in which constant shift amounts should be masked to modulo the number of bits in the operand; however, we did not fix the analogous case for shifts incorporated into the second register argument of ALU instructions that support integrated shifts. This failure to mask resulted in illegal instructions being generated, e.g. in https://bugzilla.mozilla.org/show_bug.cgi?id=1653502. This PR fixes the issue by masking the amount, as the shift semantics require.