[cfe-commits] r58440 - /cfe/trunk/lib/Analysis/GRExprEngine.cpp

[Ted Kremenek]

On Oct 30, 2008, at 9:44 PM, Zhongxing Xu wrote:

> On Fri, Oct 31, 2008 at 12:27 PM, Ted Kremenek <kremenek at apple.com>  
> wrote:
>
> On Oct 30, 2008, at 7:56 PM, Zhongxing Xu wrote:
>
> Hi Ted,
>
> Would visiting the InitList from right to left lead to some bugs?  
> For example:
>
> int x = 3;
> int a[3] = {1, x = 1, 2*x+3};
>
> At last a should be { 1, 1, 5 }. But visit from right to left  
> results { 1, 1, 9 }
>
> I don't think the order of evaluation is defined (we should consult  
> the standard).  If there is an explicit control-flow dependency  
> between the subexpressions, we should put that explicitly in the  
> CFG.  In that case visiting the subexpressions from right-to-left or  
> left-to-right won't matter (as the expressions will have already  
> been evaluated).
>
> Agree.

Another thing I thought of is cases like the following:

int a[3] = { x = (y = 2 * x), (x = 2 * y) ? 4 : 5, x };

Here there is a bunch of control-flow, but because of the ? operator  
the expression "(x = 2 * y) ? 4" will always be evaluated first (since  
it is hoisted in the CFG as a block-level expression), even if we did  
left-to-right visitation of the the subexpressions of the  
InitListExpr.  Thus the only way to ensure a fixed order of evaluation  
is to put it in the CFG (i.e., we couldn't do it in GRExprEngine even  
if we wanted to).
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