[llvm-commits] [llvm] r52421 - /llvm/trunk/lib/CodeGen/LowerSubregs.cpp
Evan Cheng
evan.cheng at apple.com
Tue Jun 17 12:24:56 PDT 2008
Right. However, the current implementation separates SUBREG_TO_REG
from INSERT_SUBREG. The later is allowed to be coalesced away, but not
the former. For now, we'll use this distinction to determine whether
it's possible to remove (what looks like) the identity copy.
Evan
On Jun 17, 2008, at 11:16 AM, Chris Lattner wrote:
>
> On Jun 17, 2008, at 10:59 AM, Evan Cheng wrote:
>
>> Author: evancheng
>> Date: Tue Jun 17 12:59:16 2008
>> New Revision: 52421
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=52421&view=rev
>> Log:
>> It's not safe to remove SUBREG_TO_REG that looks like identity
>> copies, e.g. movl %eax, %eax on x86-64 actually does a zero-extend.
>
> It sounds like we need a "movl %eax, %eax" that is a copy, and a
> separate "movl %eax, %eax" machine instr that is a zeroextend.
>
> -Chris
>
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