shithub: scc

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Optimize the generation of the preambule

If the size of the stack frame is smaller than 6 bytes then is better
to use PUSH instructions that generate the ADD HL,SP sequence.

--- a/cc2/cgen.c

+++ b/cc2/cgen.c

@@ -350,21 +350,27 @@

 generate(void)

 {

 	extern char odebug;

-	char frame = curfun->u.f.locals != 0 || odebug;

+	uint8_t i, size = curfun->u.f.locals;

+	char frame =  size != 0 || odebug;

 	if (frame) {

-		code(PUSH, NULL, regs[IX]);

-		code(MOV, regs[IX], regs[SP]);

-		code(MOV, regs[HL], imm(-curfun->u.f.locals, &l_int16));

-		code(ADD, regs[HL], regs[SP]);

-		code(MOV, regs[SP], regs[HL]);

+		code(PUSH, NULL, &reg_IX);

+		code(MOV, &reg_IX, &reg_SP);

+		if (size > 6) {

+			code(MOV, &reg_HL, imm(-size, &l_int16));

+			code(ADD, &reg_HL, &reg_SP);

+			code(MOV, &reg_SP, &reg_HL);

+		} else {

+			for (i = size; i != 0; i-= 2)

+				code(PUSH, NULL, &reg_HL);

+		}

 	}

 	apply(applycgen);

 	if (frame) {

-		code(MOV, regs[SP], regs[IX]);

-		code(POP, regs[IX], NULL);

+		code(MOV, &reg_SP, &reg_IX);

+		code(POP, &reg_IX, NULL);

 		code(RET, NULL, NULL);

 	}

 }