Designs for better debug info in GCC

Alexandre Oliva
Wed Dec 19 20:07:00 GMT 2007

On Dec 19, 2007, "Daniel Berlin" <> wrote:

> Here is the easy one:

> z_5 = a_3 + b_3
> x_4 = z_5 + c_3

> DEBUG(x, x_4)

> Reassoc may transform this into:

> z_5 = c_3 + b_3
> x_4 = z_5 + a_3

> DEBUG(x, x_4)

> Now x has the wrong value.

As Andrew said, no, it doesn't.

Now, if z_5 were present in a debug expression, then it would need
adjusting.  No different from the adjusting need for any other
instruction in which z_5 was present, though.  That's what I mean when
I talk about letting the optimizers do their job on debug instructions

Alexandre Oliva
FSF Latin America Board Member
Red Hat Compiler Engineer   aoliva@{,}
Free Software Evangelist  oliva@{,}

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