[LLVMdev] "equivalent" .ll files diverge after optimizations are applied

[Chris Lattner]

On Sep 1, 2010, at 9:43 AM, Bob Wilson wrote:

> 
> On Aug 31, 2010, at 10:19 PM, Chris Lattner wrote:
>> 
>> Hi Argiris,
>> 
>> The real problem here is that the X86 backend is turning datatypes like <1 x i64> into MMX operations, but doesn't do so in a safe way (it's not inserting the requisite EMMS instructions).  After discussing this with Dale and Bill, the right fix is to stop mapping generic vectors onto MMX operations.  This will define away the existing -disable-mmx flag and make stuff like this impossible.
>> 
>> However, this isn't going to happen in the next couple days, certainly not in time for the 2.8 release branch on friday.  As such, I checked in a horrible hack in r112696 that prevents SRoA from introducing mmx specific vector types.  I'm not aware of a target where those datatypes are actually useful, so this shouldn't be bad.  On your testcase, no mmx operations are produced.
> 
> Those types are all used with NEON.  I'll try to do some experiments to measure the impact of this....

If it matters, I can conditionalize the hack on the target triple being i386/x86-64.  Just let me know.

-Chris