[LLVMdev] RFC: llvm-convert.cpp Patch

[Dale Johannesen]

On Nov 7, 2007, at 12:16 AM, Bill Wendling wrote:
> On Nov 6, 2007, at 6:07 PM, Dale Johannesen wrote:
>>
>> Not sure I'm getting it, is this Bar itself or the constructed C.0
>> that's getting realigned?
>>
> It's C.0 that's getting realigned.

OK then, it looks like other people have made the points I was going  
to, but briefly:

Using DECL_USER_ALIGN is wrong; that is for user-specified  
alignments, and if
you use it for something else, you'll break that.

The alignment on memcpy needs to take both the source & destination  
into account.
You seem to have gotten this far.  Unfortunately that bit of llvm- 
convert is a maze of
recursive little passages, but your last patch seems to be thinking  
along the right lines.

Would it be terrible to drop the alignment on memcpy altogether?  The  
source and
destination have alignments and llvm should be able to figure out  
what the safe
alignment is for memcpy.  This is a target-dependent decision anyway;  
misaligned
loads are a good idea on some targets, not on others.