[llvm-dev] Change memcpy/memmove/memset to have dest and source alignment attributes
Hal Finkel via llvm-dev
llvm-dev at lists.llvm.org
Tue Jan 2 12:19:16 PST 2018
On 01/02/2018 02:11 PM, Daniel Neilson via llvm-dev wrote:
> Good day all,
> I’ve spent a few days resurrecting the circa-2015 work on removing
> the explicit alignment argument (4th arg) from the
> @llvm.memcpy/memmove/memset intrinsics in favour of using the
> alignment attribute on the pointer args of calls to the intrinsic.
> This work was first proposed back in August 2015 by Lang Hames:
> http://lists.llvm.org/pipermail/llvm-dev/2015-August/089384.html (item 2)
> and an attempt at landing the work was made by Pete Cooper in
> November 2015, but then backed out due to unspecified bot failures:
> I’ve prepared changes for LLVM, Clang, and Polly that are now up for
> * https://reviews.llvm.org/D41675 (LLVM part)
> * https://reviews.llvm.org/D41676 (polly part)
> * https://reviews.llvm.org/D41677 (Clang part)
> Importantly for those maintaining downstream users of the LLVM API,
> this changes the prototypes for the @llvm.memcpy/memmove/memset
> intrinsics and changes the IRBuilder API for creating memcpy and
> memmove calls.
> For example, IR which used to read:
> call void @llvm.memcpy.p0i8.p0i8.i32(i8* %dest, i8* %src, i32
> 100, i32 4, i1 false)
> will now read
> call void @llvm.memcpy.p0i8.p0i8.i32(i8* align 4 %dest, i8* align
> 4 %src, i32 100, i1 false)
> The LLVM change includes auto upgrade of the old IR. However, match
> expressions in IR tests and calls to IRBuilder’s CreateMemCpy &
> CreateMemMove will need to be updated.
> My plan is to post another note to the list when the change is
> landed, and stable.
> Comments? Concerns?
Thanks for working on this. This still seems like the right thing to do
(and will let us represent separate source and destination alignments).
> Daniel Neilson, Ph.D.
> Azul Systems
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory
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