IIRC the first (unusable) Windows version was written in Pascal.
I remember reading somewhere that Pascal calling convention was more efficient. Return from a function and cleaning the parameters from the stack could be done with a single RET N instruction, while C calls needed both a RET and a separate stack realignment, because C allows variable number of params.
I don't know if it's still the case with recent processors.
C requires that variable-argument-list fuctions be called with a correct prototype in scope, so it is perfectly feasible to use a "callee-cleans-up" ("Pascal") calling convention for regular C functions and a "caller cleans up" ("cdecl") convention for varargs functions.
The point is moot though, because just because an operation can be represented using a single assembler mnemonic doesn't mean that it's any faster than an alternative that uses several. A case in point is the "REP MOVS" style string functions, that until very recently were actually slower than opencoding the equivalents, since they trapped to microcode.
I remember reading somewhere that Pascal calling convention was more efficient. Return from a function and cleaning the parameters from the stack could be done with a single RET N instruction, while C calls needed both a RET and a separate stack realignment, because C allows variable number of params.
I don't know if it's still the case with recent processors.