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py/emitnative: Emit shorter exception handler entry code on RV32.

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This commit improves the RV32 code sequence that is emitted if a
function needs to set up an exception handler as its prologue.

The old code would clear a temporary register and then copy that value
to places that needed to be initialised with zero values.  On RV32
there's a dedicated register that's hardwired to be equal to zero, which
allows us to bypass the extra register clear and use the zero register
to initialise values.

Signed-off-by: Alessandro Gatti <a.gatti@frob.it>
This commit is contained in:
Alessandro Gatti
2025-01-24 00:20:39 +01:00
committed by Damien George
parent bfc0d7b0b9
commit 40585eaa8f
2 changed files with 12 additions and 5 deletions
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15
py/emitnative.c
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@@ -288,6 +288,11 @@ struct _emit_t {
ASM_T *as;
};
#ifndef REG_ZERO
#define REG_ZERO REG_TEMP0
#define ASM_CLR_REG(state, rd) ASM_XOR_REG_REG(state, rd, rd)
#endif
static void emit_load_reg_with_object(emit_t *emit, int reg, mp_obj_t obj);
static void emit_native_global_exc_entry(emit_t *emit);
static void emit_native_global_exc_exit(emit_t *emit);
@@ -1200,12 +1205,12 @@ static void emit_native_global_exc_entry(emit_t *emit) {
ASM_JUMP_IF_REG_ZERO(emit->as, REG_RET, start_label, true);
} else {
// Clear the unwind state
ASM_XOR_REG_REG(emit->as, REG_TEMP0, REG_TEMP0);
ASM_MOV_LOCAL_REG(emit->as, LOCAL_IDX_EXC_HANDLER_UNWIND(emit), REG_TEMP0);
ASM_CLR_REG(emit->as, REG_ZERO);
ASM_MOV_LOCAL_REG(emit->as, LOCAL_IDX_EXC_HANDLER_UNWIND(emit), REG_ZERO);
// clear nlr.ret_val, because it's passed to mp_native_raise regardless
// of whether there was an exception or not
ASM_MOV_LOCAL_REG(emit->as, LOCAL_IDX_EXC_VAL(emit), REG_TEMP0);
ASM_MOV_LOCAL_REG(emit->as, LOCAL_IDX_EXC_VAL(emit), REG_ZERO);
// Put PC of start code block into REG_LOCAL_1
ASM_MOV_REG_PCREL(emit->as, REG_LOCAL_1, start_label);
@@ -1221,8 +1226,8 @@ static void emit_native_global_exc_entry(emit_t *emit) {
ASM_JUMP_IF_REG_NONZERO(emit->as, REG_RET, global_except_label, true);
// Clear PC of current code block, and jump there to resume execution
ASM_XOR_REG_REG(emit->as, REG_TEMP0, REG_TEMP0);
ASM_MOV_LOCAL_REG(emit->as, LOCAL_IDX_EXC_HANDLER_PC(emit), REG_TEMP0);
ASM_CLR_REG(emit->as, REG_ZERO);
ASM_MOV_LOCAL_REG(emit->as, LOCAL_IDX_EXC_HANDLER_PC(emit), REG_ZERO);
ASM_JUMP_REG(emit->as, REG_LOCAL_1);
// Global exception handler: check for valid exception handler