Re: Odd GCC Behavior
Re: Odd GCC Behavior
- Subject: Re: Odd GCC Behavior
- From: "Clark Cox" <email@hidden>
- Date: Mon, 30 Jun 2008 09:26:50 -0700
On Mon, Jun 30, 2008 at 6:38 AM, J. Aaron Pendergrass
<email@hidden> wrote:
> I'm aware that this is undefined.
> I did explicitly say that the C spec leaves this unspecified.
> But {1,2,7,4} seems like such an odd choice. Especially when looking at the
> disassembly:
>
> lwz r2,56(r30)
> addi r2,r2,-8
> lwz r9,0(r2)
> lwz r2,56(r30)
> addi r0,r2,-4
> stw r0,56(r30)
> lwz r2,56(r30)
> lwz r0,0(r2)
> add r0,r9,r0
> lwz r2,56(r30)
> addi r2,r2,-8
> stw r0,0(r2)
>
> which really seems to be going out of its way to implement a fairly
> unintuitive semantics
> for this piece of undefined behavior and I was curious what the motivation
> behind this behavior might be.
With undefined behavior, there is no such thing as an "odd choice".
There is no choice to be made.
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