1 files changed, 34 insertions, 13 deletions

diff --git a/clang/lib/Sema/SemaOverload.cpp b/clang/lib/Sema/SemaOverload.cpp
index 34ac5c16470..d730bb27a1f 100644
--- a/clang/lib/Sema/SemaOverload.cpp
+++ b/clang/lib/Sema/SemaOverload.cpp
@@ -6189,6 +6189,24 @@ Sema::SelectBestMethod(Selector Sel, MultiExprArg Args, bool IsInstance,
   return nullptr;
 }
 
+// specific_attr_iterator iterates over enable_if attributes in reverse, and
+// enable_if is order-sensitive. As a result, we need to reverse things
+// sometimes. Size of 4 elements is arbitrary.
+static SmallVector<EnableIfAttr *, 4>
+getOrderedEnableIfAttrs(const FunctionDecl *Function) {
+  SmallVector<EnableIfAttr *, 4> Result;
+  if (!Function->hasAttrs())
+    return Result;
+
+  const auto &FuncAttrs = Function->getAttrs();
+  for (Attr *Attr : FuncAttrs)
+    if (auto *EnableIf = dyn_cast<EnableIfAttr>(Attr))
+      Result.push_back(EnableIf);
+
+  std::reverse(Result.begin(), Result.end());
+  return Result;
+}
+
 static bool
 convertArgsForAvailabilityChecks(Sema &S, FunctionDecl *Function, Expr *ThisArg,
                                  ArrayRef<Expr *> Args, Sema::SFINAETrap &Trap,
@@ -6262,9 +6280,9 @@ convertArgsForAvailabilityChecks(Sema &S, FunctionDecl *Function, Expr *ThisArg,
 
 EnableIfAttr *Sema::CheckEnableIf(FunctionDecl *Function, ArrayRef<Expr *> Args,
                                   bool MissingImplicitThis) {
-  auto EnableIfAttrs = Function->specific_attrs<EnableIfAttr>();
-
-  if (EnableIfAttrs.begin() == EnableIfAttrs.end())
+  SmallVector<EnableIfAttr *, 4> EnableIfAttrs =
+      getOrderedEnableIfAttrs(Function);
+  if (EnableIfAttrs.empty())
     return nullptr;
 
   SFINAETrap Trap(*this);
@@ -6274,7 +6292,7 @@ EnableIfAttr *Sema::CheckEnableIf(FunctionDecl *Function, ArrayRef<Expr *> Args,
   if (!convertArgsForAvailabilityChecks(
           *this, Function, /*ThisArg=*/nullptr, Args, Trap,
           /*MissingImplicitThis=*/true, DiscardedThis, ConvertedArgs))
-    return *EnableIfAttrs.begin();
+    return EnableIfAttrs[0];
 
   for (auto *EIA : EnableIfAttrs) {
     APValue Result;
@@ -8923,21 +8941,24 @@ static Comparison compareEnableIfAttrs(const Sema &S, const FunctionDecl *Cand1,
     return Cand1Attr ? Comparison::Better : Comparison::Worse;
   }
 
-  auto Cand1Attrs = Cand1->specific_attrs<EnableIfAttr>();
-  auto Cand2Attrs = Cand2->specific_attrs<EnableIfAttr>();
+  // FIXME: The next several lines are just
+  // specific_attr_iterator<EnableIfAttr> but going in declaration order,
+  // instead of reverse order which is how they're stored in the AST.
+  auto Cand1Attrs = getOrderedEnableIfAttrs(Cand1);
+  auto Cand2Attrs = getOrderedEnableIfAttrs(Cand2);
+
+  // It's impossible for Cand1 to be better than (or equal to) Cand2 if Cand1
+  // has fewer enable_if attributes than Cand2.
+  if (Cand1Attrs.size() < Cand2Attrs.size())
+    return Comparison::Worse;
 
   auto Cand1I = Cand1Attrs.begin();
   llvm::FoldingSetNodeID Cand1ID, Cand2ID;
-  for (auto Cand2A : Cand2Attrs) {
+  for (auto &Cand2A : Cand2Attrs) {
     Cand1ID.clear();
     Cand2ID.clear();
 
-    // It's impossible for Cand1 to be better than (or equal to) Cand2 if Cand1
-    // has fewer enable_if attributes than Cand2.
-    if (Cand1I == Cand1Attrs.end())
-      return Comparison::Worse;
-    auto Cand1A = Cand1I++;
-
+    auto &Cand1A = *Cand1I++;
     Cand1A->getCond()->Profile(Cand1ID, S.getASTContext(), true);
     Cand2A->getCond()->Profile(Cand2ID, S.getASTContext(), true);
     if (Cand1ID != Cand2ID)