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

[Paul Walker via llvm-commits]

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@@ -374,6 +424,24 @@ std::optional<VFInfo> VFABI::tryDemangleForVFABI(StringRef MangledName,
   if (Parameters.empty())
     return std::nullopt;
 
+  // Figure out the number of lanes in vectors for this function variant. This
+  // is easy for fixed length, as the vlen encoding just gives us the value
+  // directly. However, if the vlen mangling indicated that this function
+  // variant expects scalable vectors, then we need to figure out the minimum
+  // based on the widest scalar types in vector arguments.
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paulwalker-arm wrote:

The `then we need to figure out the minimum based on the widest scalar types in vector arguments` part doesn't really belong here given that the secret source provided by getScalableECFromSignature. 

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