[LLVMdev] Memcpy / Memset for address spaces >= 256 (original) (raw)

Jeremy Lakeman Jeremy.Lakeman at gmail.com
Wed Mar 12 02:53:43 PDT 2014

So a set of target specific legalisation passes? Like from the recent "PNaCl's IR simplification passes" discussion.

On Wed, Mar 12, 2014 at 7:18 PM, David Chisnall <David.Chisnall at cl.cam.ac.uk

wrote:

I have some patches that automatically expand all memcpy and similar if the operands are not in AS 0. I think this is probably not quite the right approach though, and we should be asking the back end for the function that does a memcpy / memset / whatever in a non-0 address space, and expand automatically if it doesn't provide one.

In an ideal world, I'd rather have the memcpy / memset lowering moved entirely out of SelectionDAG and into a FunctionPass, where it would be much easier to debug. I'd also want to do the same for lowering of unaligned loads / stores, so by the time you get to the back end every load and store is something that can map trivially to a single instruction (assuming an adequate addressing mode exists). David On 11 Mar 2014, at 22:23, Manuel Jacob <me at manueljacob.de> wrote: > Hi, > > SelectionDAGBuilder doesn't know how to lower a Memcpy and Memset if one of the pointer operands have an address space >= 256. This is understandable since the libc's memcpy / memset don't work for these address spaces. However, both Clang (when copying a struct) and some optimization passes (LoopIdiomRecognize, MemCpyOpt) can emit memcpy / memset for these address spaces. This triggers an assert in SelectionDAGBuilder. The optimization passes could be modified to give up when they encounter an address space >= 256, but I think clang would need some new code that emits a struct copy member-by-member. I think it's better to extend the code generator to be able to emit code for that. What do you think? > > The problem is also described here: http://llvm.org/bugs/showbug.cgi?id=18549 > > -Manuel _> ________________________ > LLVM Developers mailing list > LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

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