[clang] nonblocking/nonallocating attributes (was: nolock/noalloc) (PR #84983)

[Aaron Ballman via cfe-commits]

================
@@ -2743,3 +2759,153 @@ bool Sema::isDeclaratorFunctionLike(Declarator &D) {
   });
   return Result;
 }
+
+FunctionEffectDifferences::FunctionEffectDifferences(
+    const FunctionEffectsRef &Old, const FunctionEffectsRef &New) {
+
+  FunctionEffectsRef::iterator POld = Old.begin();
+  FunctionEffectsRef::iterator OldEnd = Old.end();
+  FunctionEffectsRef::iterator PNew = New.begin();
+  FunctionEffectsRef::iterator NewEnd = New.end();
+
+  while (true) {
+    int cmp = 0;
+    if (POld == OldEnd) {
+      if (PNew == NewEnd)
+        break;
+      cmp = 1;
+    } else if (PNew == NewEnd)
+      cmp = -1;
+    else {
+      FunctionEffectWithCondition Old = *POld;
+      FunctionEffectWithCondition New = *PNew;
+      if (Old.Effect.kind() < New.Effect.kind())
+        cmp = -1;
+      else if (New.Effect.kind() < Old.Effect.kind())
+        cmp = 1;
+      else {
+        cmp = 0;
+        if (Old.Cond.expr() != New.Cond.expr()) {
+          // TODO: Cases where the expressions are equivalent but
+          // don't have the same identity.
+          push_back(FunctionEffectDiff{
+              Old.Effect.kind(), FunctionEffectDiff::Kind::ConditionMismatch,
+              Old, New});
+        }
+      }
+    }
+
+    if (cmp < 0) {
+      // removal
+      FunctionEffectWithCondition Old = *POld;
+      push_back(FunctionEffectDiff{
+          Old.Effect.kind(), FunctionEffectDiff::Kind::Removed, Old, {}});
+      ++POld;
+    } else if (cmp > 0) {
+      // addition
+      FunctionEffectWithCondition New = *PNew;
+      push_back(FunctionEffectDiff{
+          New.Effect.kind(), FunctionEffectDiff::Kind::Added, {}, New});
+      ++PNew;
+    } else {
+      ++POld;
+      ++PNew;
+    }
+  }
+}
+
+bool FunctionEffectDiff::shouldDiagnoseConversion(
+    QualType SrcType, const FunctionEffectsRef &SrcFX, QualType DstType,
+    const FunctionEffectsRef &DstFX) const {
+
+  switch (EffectKind) {
+  case FunctionEffect::Kind::NonAllocating:
+    // nonallocating can't be added (spoofed) during a conversion, unless we
+    // have nonblocking
+    if (DiffKind == Kind::Added) {
+      for (const auto &CFE : SrcFX) {
+        if (CFE.Effect.kind() == FunctionEffect::Kind::NonBlocking)
+          return false;
+      }
+    }
+    [[fallthrough]];
+  case FunctionEffect::Kind::NonBlocking:
+    // nonblocking can't be added (spoofed) during a conversion.
+    switch (DiffKind) {
+    case Kind::Added:
+      return true;
+    case Kind::Removed:
+      return false;
+    case Kind::ConditionMismatch:
+      // TODO: Condition mismatches are too coarse right now -- expressions
----------------
AaronBallman wrote:

```suggestion
      // FIXME: Condition mismatches are too coarse right now -- expressions
```

https://github.com/llvm/llvm-project/pull/84983