shithub: scc

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Add optimization for SUB to

SUB accept the same optimizations that ADD, is only to change a
variable.

--- a/cc2/cc2.h

+++ b/cc2/cc2.h

@@ -134,7 +134,8 @@

 	RET,

 	NOP,

 	INC,

-	SUB

+	SUB,

+	DEC

 };

 enum {

--- a/cc2/code.c

+++ b/cc2/code.c

@@ -32,7 +32,8 @@

 	[RET] = inst0,

 	[NOP] = inst0,

 	[INC] = inst1,

-	[SUB] = inst2

+	[SUB] = inst2,

+	[DEC] = inst1

 };

 static char *insttext[] = {

@@ -47,7 +48,8 @@

 	[RET] = "RET",

 	[NOP] = "NOP",

 	[INC] = "INC",

-	[SUB] = "SUB"

+	[SUB] = "SUB",

+	[DEC] = "DEC"

 };

 Inst *pc, *prog;

--- a/cc2/peep.c

+++ b/cc2/peep.c

@@ -10,6 +10,7 @@

 {

 	Addr to, from;

 	TINT i;

+	uint8_t op;

 	for (pc = prog; pc; pc = pc->next) {

 		to = pc->to;

@@ -16,13 +17,15 @@

 		from = pc->from;

 		switch (pc->op) {

+		case SUB:

 		case ADD:

 			if (from.kind == CONST) {

 				if ((i = from.u.i) == 0 || i < 4) {

 					delcode();

+					op = (pc->op == ADD) ? INC : DEC;

 					while (i--)

-						inscode(INC, &to, NULL);

+						inscode(op, &to, NULL);

 				}

 			/* TODO: More optimizations (ex: -1) */

 			}