[llvm] [clang] [clang] report inlining decisions with -Wattribute-{warning|error} (PR #73552)

[Nick Desaulniers via cfe-commits]

================
@@ -449,3 +451,22 @@ void DiagnosticInfoDontCall::print(DiagnosticPrinter &DP) const {
   if (!getNote().empty())
     DP << ": " << getNote();
 }
+
+SmallVector<StringRef> DiagnosticInfoDontCall::getInliningDecisions() const {
+  SmallVector<StringRef> InliningDecisions;
+
+  if (MDN) {
+    const MDOperand &MO = MDN->getOperand(0);
+    if (auto *MDT = dyn_cast<MDTuple>(MO)) {
----------------
nickdesaulniers wrote:

Copying @aeubanks 's [comment](https://reviews.llvm.org/D141451#inline-1446137) from the phab review:

> seems simpler if this is always a MDTuple instead of special casing one entry to be MDString

For the life of me I cannot figure out why when an MDTuple is created via:
```c++
Metadata *MD = MDString::get(CI->getContext(), CalledFunc->getName());
MDTuple *MDT = MDNode::get(CI->getContext(), {MD});
CI->setMetadata("inlined.from", MDT);
```
you get
```llvm
!10 = !{!"my_memcpy"}
```

but when you copy a `MDTuple` and then append to it, you get a layer of indirection:
```c++
Metadata *MD = MDString::get(CI->getContext(), CalledFunc->getName());                                                                                                                                                   
if (MDNode *N = CI->getMetadata("inlined.from")) {                                                                                                                                                                       
  TempMDTuple Temp = cast<MDTuple>(N)->clone();                                                                                                                                                                          
  Temp->push_back(MD);                                                                                                                                                                                                   
  MD = MDNode::replaceWithUniqued(std::move(Temp));                                                                                                                                                                      
}                                                                                                                                                                                                                        
MDTuple *MDT = MDNode::get(CI->getContext(), {MD});                                                                                                                                                                      
CI->setMetadata("inlined.from", MDT);
```
```llvm
!10 = !{!11}
!11 = !{!"my_memcpy", !"my_driver"}
```
when I would have expected:
```llvm
!10 = !{!"my_memcpy", !"my_driver"}
```
am I holding the API wrong??

https://github.com/llvm/llvm-project/pull/73552