shithub: mc

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Don't eliminate all record of prepainted liveness.

	If we have a prepainted register that we coalesced, we
	can't eliminate the move, because that means we could
	clobber it.

--- a/6/ra.c

+++ b/6/ra.c

@@ -1129,13 +1129,14 @@

 	return remapped;

 }

-static int nopmov(Insn *insn)

+static int nopmov(Isel *s, Insn *insn)

 {

-	if (insn->op != Imov && insn->op != Imovs)

+	if (insn->op != Imov)

 		return 0;

 	if (insn->args[0]->type != Locreg || insn->args[1]->type != Locreg)

 		return 0;

-	return insn->args[0]->reg.id == insn->args[1]->reg.id;

+	/* Prepainted register moves need to be kept live to avoid coalescing over them */

+	return insn->args[0]->reg.id == insn->args[1]->reg.id && !bshas(s->prepainted, insn->args[0]->reg.id);

 }

 void replacealias(Isel *s, Loc **map, size_t nreg, Insn *insn)

@@ -1198,7 +1199,7 @@

 	for (j = bb->ni; j > 0; j--) {

 		insn = bb->il[j - 1];

 		replacealias(s, aliasmap, s->nreg, insn);

-		if (nopmov(insn))

+		if (nopmov(s, insn))

 			continue;

 		nuse = uses(insn, use);

 		ndef = defs(insn, def);