Messages in this thread | | | Subject | Re: [PATCH] s390 (7/13): gcc 3.3 adaptions. | From | Andreas Schwab <> | Date | Tue, 25 Feb 2003 16:39:53 +0100 |
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Linus Torvalds <torvalds@transmeta.com> writes:
|> On Tue, 25 Feb 2003, Andreas Schwab wrote: |> > |> |> > |> The point is that the compiler should see that the run-time value of i is |> > |> _obviously_never_negative_ and as such the warning is total and utter |> > |> crap. |> > |> > This requires a complete analysis of the loop body, which means that the |> > warning must be moved down from the front end (the common type of the |> > operands only depends on the type of the operands, not of any current |> > value of the expressions). |> |> So? Gcc does that anyway. _Any_ good compiler has to.
But the point is that determining the common type does not require _any_ kind of data flow analysis, and this is the place where the unsigned warning is generated.
|> Trivial example: |> |> int x[2][2]; |> |> int main(int argc, char **argv) |> { |> return x[1][-1]; |> } |> |> |> the above is actually a well-defined C program, and 100% |> standards-conforming ("strictly conforming").
This isn't as trivial as it seems. Look in comp.std.c for recent discussions on this topic (out-of-array references).
Andreas.
-- Andreas Schwab, SuSE Labs, schwab@suse.de SuSE Linux AG, Deutschherrnstr. 15-19, D-90429 Nürnberg Key fingerprint = 58CA 54C7 6D53 942B 1756 01D3 44D5 214B 8276 4ED5 "And now for something completely different." - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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