[llvm] [ConstantFolding] Implement canConstantFoldCallTo() using TLI (PR #221903)

[Ramkumar Ramachandra via llvm-commits]

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artagnon wrote:

Is it not necessary to pass GetTLI() in FunctionSpecialization?

```cpp
Constant *InstCostVisitor::visitCallBase(CallBase &I) {
  assert(LastVisited != KnownConstants.end() && "Invalid iterator!");

  Function *F = I.getCalledFunction();
  if (!F || !canConstantFoldCallTo(&I, F))
    return nullptr;
```

Is it possible then to make TLI non-optional, so callers don't forget to pass it?

https://github.com/llvm/llvm-project/pull/221903