[mypyc] feat: further optimize equality check with string literals #19883
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This PR further optimizes string equality checks against literals by getting rid of the PyUnicode_GET_LENGTH call against the literal value, which is not necessary since the value is known at compile-time
I think this optimization will be helpful in cases where the non-literal string DOES match but is actually a subtype of string (actual strings instances that match would be caught by the identity check), or in cases where an exact string does NOT match. But we can also extend this implementation to use c-strings in certain cases where we know at compile-time that the literal value is compact ascii. Actually, maybe I should do that now? Thoughts?