[LLVMdev] minimum function ir

[Reed Kotler]

On 04/22/2013 08:24 AM, Joe Groff wrote:
> On Mon, Apr 22, 2013 at 8:09 AM, Pete Couperus <pjcoup at gmail.com
> <mailto:pjcoup at gmail.com>> wrote:
>
>     Hello Reed,
>
>     Basic blocks need to end with a terminator instruction.
>     There is an "unreachable" terminator instruction, whose
>     documentation says:
>     "the presence of this instruction indicates some higher level
>     knowledge that the end of the block cannot be reached."
>     (see include/llvm/IR/Instructions.h).
>     I've been able to suppress the return using this.  I'm not
>     completely clear if this would be the right use for your scenario.
>
>
> This is the right thing to do. If your inline assembly always transfers
> code out of the block, then the end of the block is indeed unreachable.
> You do need to ensure that the asm expression has the "sideeffect"
> attribute so that it doesn't get optimized away.
>
> -Joe
>
>
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Cool. That worked for me.

So I think that clang should replace "return instruction" with 
"unreachable instruction" if the "naked" attribute is present.

The only issue here is that targets need to declare whether they support 
"naked".