Use ByteString to represent Cmm string literals (#16198)

Also used ByteString in some other relevant places.

mentioned in issue #16198 (closed)

Sounds reasonable to me.

My only slight concern is about fragmentation due to the pinned nature of ByteStrings. Particularly in the case of long-lived compiler runs (e.g. the GHCi sessions that @simonmar and his group are known to use). We could in principle introduce our own unpinned byte array type into GHC but perhaps this is best left for future work.

We already pay the price of pinned ByteStrings in Core. GHCi uses Core to ByteCode transformation (except with -fobject-code), so no Cmm involved afaik.

We could use ByteArrays but it would be a much more invasive change.

Could there be a Note giving an overview of the handling of string literals, in the way this patch does it? Stressing the efficiency issues that led to the change?

You know the details now! Writing them down, and then referring to that Note from appropriate places, would be a help. Thanks!

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• cbdec328...a1e9cd6a - 33 commits from branch ghc:master
• 9e9552d8 - Use ByteString to represent Cmm string literals (#16198 (closed))
• 166f48ab - Optimize pprASCII

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Sounds good to me. I'm not sure that changing [Word8] to ByteString really deserves a full Note.

Thanks. Indeed I don't really know what to put in the note. It was probably an oversight to use [Word8] instead of FastBytes/ByteString to begin with.

mentioned in merge request !143 (merged)

approved this merge request

Let's do this!

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• 166f48ab...8c3133a6 - 12 commits from branch ghc:master
• 44eb3ca9 - Use ByteString to represent Cmm string literals (#16198 (closed))
• 9f973dc0 - Optimize pprASCII

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enabled an automatic merge when the pipeline for 9f973dc0 succeeds

mentioned in merge request !141 (merged)

assigned to @marge-bot

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• 9f973dc0...a5373c1f - 11 commits from branch ghc:master
• 2f2fabdc - Use ByteString to represent Cmm string literals (#16198 (closed))
• a5a7adb2 - Optimize pprASCII

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assigned to @hsyl20

I couldn't merge this branch: CI failed!

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• a5a7adb2...7cdcd3e1 - 48 commits from branch ghc:master
• f9abab52 - Use ByteString to represent Cmm string literals (#16198 (closed))
• 430ebfc3 - Optimize pprASCII

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assigned to @marge-bot

assigned to @hsyl20