Avoid negation of signed integers in C that may hold INT*_MIN.

Reported by minoki.
Recent C compilers 'take advantage' of the undefined behavior.
This completely changes the meaning of expressions like (k == -k).

1 files changed, 1 insertions, 1 deletions

diff --git a/src/lj_asm_mips.h b/src/lj_asm_mips.h
index c0e491a6..1d4c8a25 100644
--- a/src/lj_asm_mips.h
+++ b/src/lj_asm_mips.h
@@ -1227,7 +1227,7 @@ static void asm_arithov(ASMState *as, IRIns *ir)
   Reg right, left, tmp, dest = ra_dest(as, ir, RSET_GPR);
   if (irref_isk(ir->op2)) {
     int k = IR(ir->op2)->i;
-    if (ir->o == IR_SUBOV) k = -k;
+    if (ir->o == IR_SUBOV) k = (int)(~(unsigned int)k+1u);
     if (checki16(k)) {  /* (dest < left) == (k >= 0 ? 1 : 0) */
       left = ra_alloc1(as, ir->op1, RSET_GPR);
       asm_guard(as, k >= 0 ? MIPSI_BNE : MIPSI_BEQ, RID_TMP, RID_ZERO);