This pass finds all string.const and creates globals for them. After this transform, no string.const appears anywhere but in a global, and each string appears in one global which is then global.get-ed everywhere. This avoids overhead in VMs where executing a string.const is an allocation, and is also a good step towards imported strings. For that, this pass will be extended from gathering to a full lowering pass, which will first gather into globals as this pass does, and then turn each of those globals with a string.const into an imported externref. (For that reason this pass is in a file called StringLowering, as the two passes will share much of their code, and the larger pass should decide the name I think.) This pass runs in -O2 and above. Repeated executions have no downside (see details in code).