[PATCH] D103865: [SystemZ] Generate XC loop for memset 0 of variable length.

[Jonas Paulsson via Phabricator via llvm-commits]

jonpa updated this revision to Diff 355670.
jonpa marked 2 inline comments as done.
jonpa added a comment.

Updated per review.

> I was thinking of just using emitInt16 for the three words, that will show as .word in the textual assembler output, which may not be pretty but is certainly correct. (You could in addition use an emitRawComment to print a textual representation to make the file more readable).

Ah, ok, I did not realize at the time I could just print the instruction as numbers... I tried this instead now, since we don't really want to have a generic subtarget around. Is there any reason to print 3 x Int16?  Would it be better to print it as one (or three) hex if possible?

> In the meantime I thought of yet another option: the instructions used via EXRL are really part of the function containing the EXRL, and should therefore be emitted using the same Subtarget that is in effect for that function (this is not *currently* a problem, but it might be a potential issue if we want to use an EXRL target instruction that is only available in some ISA levels).

This seems like the logical solution, but it is a bit unfortunate to have to go through all of that trouble just for this case where it is actually not really needed at all.

Not sure if the best thing is to do it the manual way, or to have an extra subtarget map on the side in the SystemZAsmPrinter...

I wonder if perhaps the MC layer could have an emitInstruction() / assembleInstruction() method without the STI argument, that was only very basic that could work in cases like this... It would be nice to reuse the bits encoding already available... On the other hand if we only have EXRL targets of this one format, maybe it's ok to do it on the side...


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D103865/new/

https://reviews.llvm.org/D103865

Files:
  llvm/lib/Target/SystemZ/SystemZAsmPrinter.cpp
  llvm/lib/Target/SystemZ/SystemZAsmPrinter.h
  llvm/lib/Target/SystemZ/SystemZISelLowering.cpp
  llvm/lib/Target/SystemZ/SystemZInstrFormats.td
  llvm/lib/Target/SystemZ/SystemZInstrInfo.td
  llvm/lib/Target/SystemZ/SystemZSelectionDAGInfo.cpp
  llvm/test/CodeGen/SystemZ/memset-05.ll

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