From 053105d58552c600a2e56473592212a9bddafcd4 Mon Sep 17 00:00:00 2001
From: Douglas Gregor <dgregor@apple.com>
Date: Tue, 2 Nov 2010 00:02:34 +0000
Subject: [PATCH] When performing template argument deduction against a
 template-id, only keep deduction results for successful deductions, so that
 they can be compared against each other. Fixes PR8462, from Richard Smith!

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@117983 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Sema/SemaTemplateDeduction.cpp            | 11 ++++++++--
 .../temp.deduct/temp.deduct.call/p3.cpp       | 22 +++++++++++++++++++
 2 files changed, 31 insertions(+), 2 deletions(-)

diff --git a/lib/Sema/SemaTemplateDeduction.cpp b/lib/Sema/SemaTemplateDeduction.cpp
index 855516cf10..905e17e9c1 100644
--- a/lib/Sema/SemaTemplateDeduction.cpp
+++ b/lib/Sema/SemaTemplateDeduction.cpp
@@ -721,6 +721,8 @@ DeduceTemplateArguments(Sema &S,
           llvm::SmallVector<const RecordType *, 8> ToVisit;
           ToVisit.push_back(RecordT);
           bool Successful = false;
+          llvm::SmallVectorImpl<DeducedTemplateArgument> DeducedOrig(0);
+          DeducedOrig = Deduced;
           while (!ToVisit.empty()) {
             // Retrieve the next class in the inheritance hierarchy.
             const RecordType *NextT = ToVisit.back();
@@ -738,9 +740,14 @@ DeduceTemplateArguments(Sema &S,
                                           QualType(NextT, 0), Info, Deduced);
 
               // If template argument deduction for this base was successful,
-              // note that we had some success.
-              if (BaseResult == Sema::TDK_Success)
+              // note that we had some success. Otherwise, ignore any deductions
+              // from this base class.
+              if (BaseResult == Sema::TDK_Success) {
                 Successful = true;
+                DeducedOrig = Deduced;
+              }
+              else
+                Deduced = DeducedOrig;
             }
 
             // Visit base classes
diff --git a/test/CXX/temp/temp.fct.spec/temp.deduct/temp.deduct.call/p3.cpp b/test/CXX/temp/temp.fct.spec/temp.deduct/temp.deduct.call/p3.cpp
index 19962c5349..3c22cf349c 100644
--- a/test/CXX/temp/temp.fct.spec/temp.deduct/temp.deduct.call/p3.cpp
+++ b/test/CXX/temp/temp.fct.spec/temp.deduct/temp.deduct.call/p3.cpp
@@ -101,3 +101,25 @@ void test_f4(D d, E e, F f, G g) {
   C<int, 1> *ci3c = f4c(&g);
   int       *ip1 = f4c(&f);
 }
+
+// PR8462
+namespace N {
+  struct T0;
+  struct T1;
+
+  template<typename X, typename Y> struct B {};
+
+  struct J : B<T0,T0> {};
+  struct K : B<T1,T1> {};
+
+  struct D : J, K {};
+
+  template<typename X, typename Y> void F(B<Y,X>);
+
+  void test()
+  {
+    D d; 
+    N::F<T0>(d); // Fails
+    N::F<T1>(d); // OK
+  }
+}
-- 
2.40.0