Re: Help restricting args of an intrinsic function

[Mike Stump <mrs@apple.com>]

On Monday, February 2, 2004, at 03:26 PM, Joe Buck wrote:
> On Fri, Jan 30, 2004 at 07:59:34PM -0800, Mike Stump wrote:
>> On Friday, January 30, 2004, at 05:38  PM, Diego Novillo wrote:
>>> Yes, that's fine.  Here's what tree-ssa emits after the tree
>>> optimization passes for the test cases you mentioned.
>>
>> So, does your scheme work when the optimizer is off (-O0)?
>>
>> If not, why would that be a solution?
>
> Who says that exactly one instruction must be emitted with the 
> optimizer
> off?  It seems to me that it would suffice to have the builtin function
> emit the one instruction in the case where the mask arguments, after 
> any
> optimization, are constant, and otherwise emit whatever code is needed 
> to
> compute the correct result (or simply emit a call to a library 
> function).

This violates the users expectations.

The _point_ of having builtins for single machine instructions is so 
that the generated code will use them (or something better).  Tweaking 
a builtin to generate an external lib call or 5 instructions instead of 
using that one machine instruction isn't, uhm, winning.

The one case were it would be winning, is if you wanted to use x86 
builtins on the ppc and the compiler did its best to make it just work.