[llvm] Refactor try demangle for vfabi to use only the vector abi mangled names (PR #67430)

[Paul Walker via llvm-commits]

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@@ -434,22 +434,33 @@ std::optional<VFInfo> VFABI::tryDemangleForVFABI(StringRef MangledName,
   // need to make sure that the VF field of the VFShape class is never
   // set to 0.
   if (IsScalable) {
-    const Function *F = M.getFunction(VectorName);
-    // The declaration of the function must be present in the module
-    // to be able to retrieve its signature.
-    if (!F)
+    if (ISA != VFISAKind::SVE)
       return std::nullopt;
-    const ElementCount EC = getECFromSignature(F->getFunctionType());
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paulwalker-arm wrote:

What about keeping `getECFromSignature` but passing it the `ISA` and the `FunctionType` of the `CallInst`?

https://github.com/llvm/llvm-project/pull/67430