[PATCH][FastISel] Let the target decide first if it wants to materialize a constant.

[Juergen Ributzka]

I didn’t hear anyone object in general, so I though I will just go ahead and move this to post-commit review and incorporate feedback afterwards or revert when necessary.

-Juergen

On Aug 13, 2014, at 6:20 PM, Eric Christopher <echristo at gmail.com> wrote:

> So, this was in my list of things to look at but it seems like you
> went ahead and committed it without actually waiting for feedback?
> 
> -eric
> 
> On Tue, Aug 12, 2014 at 9:23 AM, Juergen Ributzka <juergen at apple.com> wrote:
>> ping :D
>> 
>> On Aug 7, 2014, at 2:51 PM, Juergen Ributzka <juergen at apple.com> wrote:
>> 
>>> Hi @ll,
>>> 
>>> I want to change the order in which FastISel tries to materialize a constant.
>>> 
>>> Originally it would try to use a simple target-independent approach, which can lead to the generation of inefficient code.
>>> 
>>> On X86 this would result in the use of movabsq to materialize any 64bit integer constant - even for simple and small values such as 0 and 1. Also
>>> some very funny floating-point materialization could be observed too.
>>> 
>>> On AArch64 it would materialize the constant 0 in a register even the architecture has an actual "zero" register.
>>> 
>>> On ARM it would generate unnecessary mov instructions or not use mvn, etc
>>> 
>>> I want to simply change the order and always asks the target first if it likes to materialize the constant. The patches a pretty simple and straight forward, but since it changes the way how FastISel works with respect to constants I wanted everyone affected by it to have at least a quick look first.
>>> 
>>> Thanks
>>> 
>>> Cheers,
>>> Juergen
>>> 
>>> <0001-FastISel-AArch64-Cleanup-constant-materialization-co.patch><0002-FastISel-ARM-Fix-a-bug-in-the-integer-materializatio.patch><0003-FastISel-ARM-Use-MOVT-MOVW-if-the-subtarget-requests.patch><0004-FastISel-X86-Refactor-constant-materialization.-NFCI.patch><0005-FastISel-Let-the-target-decide-first-if-it-wants-to-.patch><0006-FastISel-AArch64-Make-use-of-the-zero-register-when-.patch><0007-FastISel-X86-Emit-more-efficient-instructions-for-in.patch><0008-FastISel-X86-Use-XOR-to-materialize-the-0-value.patch>
>>