[llvm] [SVE] Don't require lookup when demangling vector function mappings (PR #72260)

[Graham Hunter via llvm-commits]

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@@ -66,24 +66,26 @@ ParseRet tryParseMask(StringRef &MangledName, bool &IsMasked) {
 /// vector length. On success, the `<vlen>` token is removed from
 /// the input string `ParseString`.
 ///
-ParseRet tryParseVLEN(StringRef &ParseString, unsigned &VF, bool &IsScalable) {
+ParseRet tryParseVLEN(StringRef &ParseString,
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huntergr-arm wrote:

That's pretty much the same thing expressed a different way -- we either have a valid non-zero fixed length VF, or we know that the VF is scalable but the minimum is yet to be determined.

It's a pity std::variant is so limited; something like Rust's enums would be great for this (or any language with sum types).

Maybe we could return a variant that's either an unsigned for a fixed VF, a dummy bool for scalable, or a ParseRet for failure?

https://github.com/llvm/llvm-project/pull/72260