Ben Gamari authored Nov 08, 2021 and Marge Bot committed Dec 02, 2021

Previously primops.txt.pp stipulated that the word-size shift primops
were only defined for shift offsets in [0, word_size). However, there
was no further guidance for the definition of Cmm's sub-word size shift
MachOps.

Here we fix this by explicitly disallowing (checked in many cases by
CmmLint) shift operations where the shift offset is larger than the
shiftee. This is consistent with LLVM's shift operations, avoiding the
miscompilation noted in #20637.