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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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6
src/lj_opt_fold.c
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@@ -236,7 +236,7 @@ static int32_t kfold_intop(int32_t k1, int32_t k2, IROp op)
case IR_SUB: k1 -= k2; break;
case IR_MUL: k1 *= k2; break;
case IR_MOD: k1 = lj_vm_modi(k1, k2); break;
case IR_NEG: k1 = -k1; break;
case IR_NEG: k1 = (int32_t)(~(uint32_t)k1+1u); break;
case IR_BAND: k1 &= k2; break;
case IR_BOR: k1 |= k2; break;
case IR_BXOR: k1 ^= k2; break;
@@ -1160,7 +1160,7 @@ LJFOLDF(simplify_intsub_k)
if (fright->i == 0) /* i - 0 ==> i */
return LEFTFOLD;
fins->o = IR_ADD; /* i - k ==> i + (-k) */
fins->op2 = (IRRef1)lj_ir_kint(J, -fright->i); /* Overflow for -2^31 ok. */
fins->op2 = (IRRef1)lj_ir_kint(J, (int32_t)(~(uint32_t)fright->i+1u)); /* Overflow for -2^31 ok. */
return RETRYFOLD;
}
@@ -1191,7 +1191,7 @@ LJFOLDF(simplify_intsub_k64)
if (k == 0) /* i - 0 ==> i */
return LEFTFOLD;
fins->o = IR_ADD; /* i - k ==> i + (-k) */
fins->op2 = (IRRef1)lj_ir_kint64(J, (uint64_t)-(int64_t)k);
fins->op2 = (IRRef1)lj_ir_kint64(J, ~k+1u);
return RETRYFOLD;
}