...The both ESP32 and ESP8266 have hardware MULL and MUL16 type instructions. The necessary code to generate the CPU specific instructions hasn't been implemented yet [1] - this target is relatively new so not much time has been invested yet into optimizing the generated code.
i have almost zero knowledge in this xtensa cpu. Is there any reason why fpc does not generate MUL* instruction, instead calling multiply helper function? missing native MUL instruction perhaps?
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Edit: [1] Not quite true, there is actually some code that can generate a hardware MULL instruction, but it is disabled by default (probably because it lacks error checking).