[llvm-commits] [llvm] r65996 - in /llvm/trunk: lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp lib/Target/X86/X86RegisterInfo.td test/CodeGen/X86/pr3701.ll

[Evan Cheng]

On Mar 5, 2009, at 9:08 AM, Dan Gohman wrote:

>
> On Mar 4, 2009, at 12:02 PM, Eli Friedman wrote:
>
>> On Wed, Mar 4, 2009 at 11:44 AM, Dan Gohman <gohman at apple.com> wrote:
>>>
>>> On Mar 3, 2009, at 6:48 PM, Evan Cheng wrote:
>>>
>>>>
>>>> On Mar 3, 2009, at 6:00 PM, Dan Gohman wrote:
>>>>
>>>>>
>>>>> On Mar 3, 2009, at 5:41 PM, Evan Cheng wrote:
>>>>>
>>>>>> Author: evancheng
>>>>>> Date: Tue Mar  3 19:41:49 2009
>>>>>> New Revision: 65996
>>>>>>
>>>>>> URL: http://llvm.org/viewvc/llvm-project?rev=65996&view=rev
>>>>>> Log:
>>>>>> Fix PR3701. 1. X86 target renamed eflags register to flags. This
>>>>>> matches what llvm-gcc generates so codegen knows flags register  
>>>>>> is
>>>>>> being clobbered by inline asm. 2. BURR scheduler should also  
>>>>>> check
>>>>>> if inline asm nodes can clobber "live" physical registers.
>>>>>> Previously it was only checking target nodes with implicit defs.
>>>>>
>>>>> What about the "~{dirflag}" part? Since DF isn't modeled
>>>>> separately, should "dirflag" be mapped to "flags"?
>>>>
>>>> Registers are matched by name. I don't see a need to special case
>>>> this
>>>> since all 3 flag registers are added to inline asm instructions.
>>>
>>> But now, IR with just "dirflag" clobbered, and not "flags", would be
>>> handled incorrectly.
>>
>> llvm-gcc is lying; inline asm doesn't clobber the direction flag.
>
>
> The comments with ix86_md_asm_clobbers suggest that dirflag is
> always marked clobbered in order to preserve compatibility with
> inline asms developed with earlier versions of GCC.
>
> But regardless, if an inline asm in LLVM IR can list "dirflag"
> as a clobber, codegen should be able to handle it correctly.

Patches welcome. :-)

>
> Also, it looks like "cc" should also get mapped to "flags".

I think it makes more sense to change llvm-gcc so it emits "flags"  
instead of "cc". I don't think we want to add register aliases to x86  
backend.

Evan


>
> Dan
>
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