From 5a9220e6798f1052bbdb4cfa96711fa5ce2f00e9 Mon Sep 17 00:00:00 2001
From: Richard Smith <richard-llvm@metafoo.co.uk>
Date: Fri, 1 Dec 2017 21:24:36 +0000
Subject: [PATCH] [c++17] When deducing the type of a non-type template
 parameter from the type of its argument, perform function-to-pointer and
 array-to-pointer decay on the parameter type first.

Otherwise deduction will fail, as the type of the argument will be decayed.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@319584 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Sema/SemaTemplateDeduction.cpp           | 5 +++--
 test/SemaTemplate/temp_arg_nontype_cxx1z.cpp | 4 ++++
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/lib/Sema/SemaTemplateDeduction.cpp b/lib/Sema/SemaTemplateDeduction.cpp
index 51f21be64a..a91c190cb0 100644
--- a/lib/Sema/SemaTemplateDeduction.cpp
+++ b/lib/Sema/SemaTemplateDeduction.cpp
@@ -354,8 +354,9 @@ static Sema::TemplateDeductionResult DeduceNonTypeTemplateArgument(
     // expanded NTTP should be a pack expansion type?
     return Sema::TDK_Success;
 
-  // Get the type of the parameter for deduction.
-  QualType ParamType = NTTP->getType();
+  // Get the type of the parameter for deduction. If it's a (dependent) array
+  // or function type, we will not have decayed it yet, so do that now.
+  QualType ParamType = S.Context.getAdjustedParameterType(NTTP->getType());
   if (auto *Expansion = dyn_cast<PackExpansionType>(ParamType))
     ParamType = Expansion->getPattern();
 
diff --git a/test/SemaTemplate/temp_arg_nontype_cxx1z.cpp b/test/SemaTemplate/temp_arg_nontype_cxx1z.cpp
index d0fb25c047..1a84d545c6 100644
--- a/test/SemaTemplate/temp_arg_nontype_cxx1z.cpp
+++ b/test/SemaTemplate/temp_arg_nontype_cxx1z.cpp
@@ -238,6 +238,10 @@ namespace Auto {
     constexpr char s[] = "test";
     template<const auto* p> struct S { };
     S<s> p;
+
+    template<typename R, typename P, R F(P)> struct A {};
+    template<typename R, typename P, R F(P)> void x(A<R, P, F> a);
+    void g(int) { x(A<void, int, &g>()); }
   }
 
   namespace DecltypeAuto {
-- 
2.50.1