Alessandro Gatti 7a69b2d786 py/asmrv32: Use Zcmp opcodes for function prologues and epilogues. ...

This commit introduces the possibility of using Zcmp opcodes when
generating function prologues and epilogues, reducing the generated code
size.

With the addition of selected Zcmp opcodes, each generated function can
be up to 30 bytes shorter and having a faster prologue and epilogue.  If
Zcmp opcodes can be used then register saving is a matter of a simple
CM.PUSH opcode rather than a series of C.SWSP opcodes.  Conversely,
register restoring is a single CM.POPRET opcode instead of a series of
C.LWSP opcodes followed by a C.JR RA opcode.  This should also lead to
faster code given that there's only one opcode doing the registers
saving rather than a series of them.

For functions that allocate less than three locals then the generated
code will allocate up to 12 bytes of unused stack space.  Whilst this is
a relatively rare occurrence for generated native and viper code,
inline assembler blocks will probably incur into this penalty.  Still,
considering that at the moment the only targets that support Zcmp
opcodes are relatively high-end MCUs (the RP2350 in RV32 mode and the
ESP32P4), this is probably not much of an issue.

Signed-off-by: Alessandro Gatti <a.gatti@frob.it>

2025-12-19 17:06:53 +11:00

25 KiB

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