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

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Reported by minoki.
Recent C compilers 'take advantage' of the undefined behavior.
This completely changes the meaning of expressions like (k == -k).
This commit is contained in:
Mike Pall
2022-12-22 00:03:06 +01:00
parent b2791179ef
commit 8a5e398c52
12 changed files with 32 additions and 32 deletions
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2
src/lj_asm_mips.h
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@@ -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);