On Sun, Aug 25, 2013 at 01:26:08AM -0700, Jonathan Kotker wrote:
> Apologies for reviving an old thread, but I'm revisiting this issue, trying
> to see if I can patch a way around it, without having to constant-fold
> floating point numbers.
>
> Looking at the suggested line (line 2656 of src/cil.ml), it does not look
> like that particular code should be throwing the error that I'm seeing,
> because it checks if the type of the result is either an int or a float
> (using 'integralType' on line 2650). Indeed, the error that I am seeing is
> the following:
>
> C:/../testGlobalInit-gt.c:5: Bug: newTempVar called outside a function
> C:/../testGlobalInit-gt.c:5: Error: global initializer
>
> Are there any suggestions on how to get this to work? Ideally, I guess I'm
> looking for a way for expressions involving floating-point values to just
> 'go through' without any changes and constant foldings, but it looks like
> that's already happening.
The problem is that the ternary operator :? is not considered an expression in
CIL (unless you use --useLogicalOperators, in which case it is represented by
Question). So when CIL encounters this operator, it translates it into a
conditional: {x = a ? b : c} becomes {if(a) x = b else x = c}.
This translation does not work for global variables, because the C syntax does
not allow you to use an if statement outside of a function. CIL tries as hard as
it can to mitigate this issue by performing constant folding, in order to
eliminate :? when it is safe to do so. When constant-folding fails, it falls
back on the if trick, which requires (in general) a temporary variable, which
cannot be allocated outside of a function, hence the error that you get.
I don't see any way to solve this issue but using Question; it has been
introduced precisely for those cases. Now, if you are reluctant to enable
--useLogicalOperators as a whole, you can enable Question selectively with this
trivial patch:
diff --git a/src/frontc/cabs2cil.ml b/src/frontc/cabs2cil.ml
index 7d7f3d9..d7fd2d9 100644
--- a/src/frontc/cabs2cil.ml
+++ b/src/frontc/cabs2cil.ml
@@ -4470,7 +4470,7 @@ and doExp (asconst: bool) (* This expression is used as
a constant *)
| Some e2' ->
finishExp (se1 @@ se2) (snd (castTo t2 tresult e2')) tresult
end
- | CEExp (se1, e1') when !useLogicalOperators && isEmpty se2 && isEmpty
se3 ->
+ | CEExp (se1, e1') when isEmpty se2 && isEmpty se3 ->
let e2' = match e2'o with
None -> (* use e1' *)
snd (castTo t2 tresult e1')
One could argue that Question should use regardless of --useLogicalOperators
when constant folding fails. If you anyone feels this is a reasonable tweak to
introduce in the next release, I'm willing to consider it (but it will of
course change the fact that Question will not be optionnal anymore).
Best regards,
--
Gabriel
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