From 38175a2e751593c24eb63679191572ed250c6d4c Mon Sep 17 00:00:00 2001
From: Richard Smith <richard-llvm@metafoo.co.uk>
Date: Wed, 28 Sep 2016 22:08:38 +0000
Subject: Fix bug where template argument deduction of a non-type template
 parameter used as a template argument in a template-id, from a null non-type
 template argument, failed.

Extracted from a patch by James Touton!

llvm-svn: 282641
---
 clang/lib/Sema/SemaTemplateDeduction.cpp | 31 ++++++++++++++++++++++++++++++-
 1 file changed, 30 insertions(+), 1 deletion(-)

(limited to 'clang/lib')

diff --git a/clang/lib/Sema/SemaTemplateDeduction.cpp b/clang/lib/Sema/SemaTemplateDeduction.cpp
index f8e825ff941..2311b2b7447 100644
--- a/clang/lib/Sema/SemaTemplateDeduction.cpp
+++ b/clang/lib/Sema/SemaTemplateDeduction.cpp
@@ -285,7 +285,7 @@ checkDeducedTemplateArguments(ASTContext &Context,
 }
 
 /// \brief Deduce the value of the given non-type template parameter
-/// from the given constant.
+/// from the given integral constant.
 static Sema::TemplateDeductionResult DeduceNonTypeTemplateArgument(
     Sema &S, NonTypeTemplateParmDecl *NTTP, const llvm::APSInt &Value,
     QualType ValueType, bool DeducedFromArrayBound, TemplateDeductionInfo &Info,
@@ -309,6 +309,32 @@ static Sema::TemplateDeductionResult DeduceNonTypeTemplateArgument(
   return Sema::TDK_Success;
 }
 
+/// \brief Deduce the value of the given non-type template parameter
+/// from the given null pointer template argument type.
+static Sema::TemplateDeductionResult DeduceNullPtrTemplateArgument(
+    Sema &S, NonTypeTemplateParmDecl *NTTP, QualType NullPtrType,
+    TemplateDeductionInfo &Info,
+    SmallVectorImpl<DeducedTemplateArgument> &Deduced) {
+  Expr *Value =
+      S.ImpCastExprToType(new (S.Context) CXXNullPtrLiteralExpr(
+                              S.Context.NullPtrTy, NTTP->getLocation()),
+                          NullPtrType, CK_NullToPointer)
+          .get();
+  DeducedTemplateArgument NewDeduced(Value);
+  DeducedTemplateArgument Result = checkDeducedTemplateArguments(
+      S.Context, Deduced[NTTP->getIndex()], NewDeduced);
+
+  if (Result.isNull()) {
+    Info.Param = NTTP;
+    Info.FirstArg = Deduced[NTTP->getIndex()];
+    Info.SecondArg = NewDeduced;
+    return Sema::TDK_Inconsistent;
+  }
+
+  Deduced[NTTP->getIndex()] = Result;
+  return Sema::TDK_Success;
+}
+
 /// \brief Deduce the value of the given non-type template parameter
 /// from the given type- or value-dependent expression.
 ///
@@ -1758,6 +1784,9 @@ DeduceTemplateArguments(Sema &S,
                                              Arg.getIntegralType(),
                                              /*ArrayBound=*/false,
                                              Info, Deduced);
+      if (Arg.getKind() == TemplateArgument::NullPtr)
+        return DeduceNullPtrTemplateArgument(S, NTTP, Arg.getNullPtrType(),
+                                             Info, Deduced);
       if (Arg.getKind() == TemplateArgument::Expression)
         return DeduceNonTypeTemplateArgument(S, NTTP, Arg.getAsExpr(),
                                              Info, Deduced);
-- 
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