[llvm] r217629 - [CodeGenPrepare] Teach the addressing mode matcher how to promote zext.

[Quentin Colombet]

> On Sep 16, 2014, at 1:41 PM, Quentin Colombet <qcolombet at apple.com> wrote:
> 
> 
>> On Sep 16, 2014, at 12:28 PM, Joerg Sonnenberger <joerg at britannica.bec.de> wrote:
>> 
>> On Thu, Sep 11, 2014 at 09:22:14PM -0000, Quentin Colombet wrote:
>>> Author: qcolombet
>>> Date: Thu Sep 11 16:22:14 2014
>>> New Revision: 217629
>>> 
>>> URL: http://llvm.org/viewvc/llvm-project?rev=217629&view=rev
>>> Log:
>>> [CodeGenPrepare] Teach the addressing mode matcher how to promote zext.
>>> I.e., teach it about 'sext (zext a to ty) to ty2' => zext a to ty2.
>> 
>> More fun, again, build with -O2.
> 
> Nice!
> This one is funny, we have in the IR 'zext i8 undef to i32’, which when it is promoted gives a constant 0 instead of ‘zext i8 undef to i64’ (because of how the IRBuilder works).

And the problem is that we expect an instruction, not a value!

> I do not know why it is valid to have 'zext i8 undef to i32’ and not 'zext i8 undef to i64’… It looks to me we shouldn’t have ''zext i8 undef to i32’ in the first place.
> 
> Looking.
> 
> -Quentin
> 
>> 
>> Joerg
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