[PATCH] D97129: [Support] unsafe pointer arithmetic in llvm_regcomp()

[Vitaly Buka via Phabricator via llvm-commits]

vitalybuka accepted this revision.
vitalybuka added inline comments.


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Comment at: llvm/lib/Support/regcomp.c:252
 #define	PEEK2()	(*(p->next+1))
-#define	MORE()	(p->next < p->end)
-#define	MORE2()	(p->next+1 < p->end)
+#define	MORE()	(p->end - p->next > 0)
+#define	MORE2()	(p->end - p->next > 1)
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vitalybuka wrote:
> MaskRay wrote:
> > vitalybuka wrote:
> > > I understand all but this line. I guess it had no UB there.
> > I think this clause applies
> > https://www.iso-9899.info/n1570.html#6.5.6p8 "...  If both the pointer operand and the result point to elements of the same array object, or one past the last element of the array object, the evaluation shall not produce an overflow; otherwise, the behavior is undefined."
> > 
> > There was a UB.
> I am aware of this rule, but I assume that end and next always "point to elements of the same array object, or one past the last element"
> So old MORE2 violates the rule, but MORE does not.
I am fine if it 's done just for consistency. But I would appreciate explanation if there is UB in MORE() as well.


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  https://reviews.llvm.org/D97129/new/

https://reviews.llvm.org/D97129