Don't allocate unused 2nd result register in JIT compiler backend.

src/lj_asm_arm.h

@@ -426,7 +426,7 @@ static void asm_gencall(ASMState *as, const CCallInfo *ci, IRRef *args)
 static void asm_setupresult(ASMState *as, IRIns *ir, const CCallInfo *ci)
 {
   RegSet drop = RSET_SCRATCH;
-  int hiop = ((ir+1)->o == IR_HIOP);
+  int hiop = ((ir+1)->o == IR_HIOP && !irt_isnil((ir+1)->t));
   if (ra_hasreg(ir->r))
     rset_clear(drop, ir->r);  /* Dest reg handled below. */
   if (hiop && ra_hasreg((ir+1)->r))

src/lj_asm_mips.h

@@ -291,7 +291,7 @@ static void asm_gencall(ASMState *as, const CCallInfo *ci, IRRef *args)
 static void asm_setupresult(ASMState *as, IRIns *ir, const CCallInfo *ci)
 {
   RegSet drop = RSET_SCRATCH;
-  int hiop = ((ir+1)->o == IR_HIOP);
+  int hiop = ((ir+1)->o == IR_HIOP && !irt_isnil((ir+1)->t));
   if ((ci->flags & CCI_NOFPRCLOBBER))
     drop &= ~RSET_FPR;
   if (ra_hasreg(ir->r))

src/lj_asm_ppc.h

@@ -298,7 +298,7 @@ static void asm_gencall(ASMState *as, const CCallInfo *ci, IRRef *args)
 static void asm_setupresult(ASMState *as, IRIns *ir, const CCallInfo *ci)
 {
   RegSet drop = RSET_SCRATCH;
-  int hiop = ((ir+1)->o == IR_HIOP);
+  int hiop = ((ir+1)->o == IR_HIOP && !irt_isnil((ir+1)->t));
   if ((ci->flags & CCI_NOFPRCLOBBER))
     drop &= ~RSET_FPR;
   if (ra_hasreg(ir->r))

src/lj_asm_x86.h

@@ -531,7 +531,7 @@ static void asm_gencall(ASMState *as, const CCallInfo *ci, IRRef *args)
 static void asm_setupresult(ASMState *as, IRIns *ir, const CCallInfo *ci)
 {
   RegSet drop = RSET_SCRATCH;
-  int hiop = (LJ_32 && (ir+1)->o == IR_HIOP);
+  int hiop = (LJ_32 && (ir+1)->o == IR_HIOP && !irt_isnil((ir+1)->t));
   if ((ci->flags & CCI_NOFPRCLOBBER))
     drop &= ~RSET_FPR;
   if (ra_hasreg(ir->r))