From 281703e67ffaee8e26efef86e0df3e145477f4cb Mon Sep 17 00:00:00 2001
From: Sam McCall <sam.mccall@gmail.com>
Date: Wed, 7 Oct 2020 16:36:38 +0200
Subject: [PATCH] Revert "[ADT] function_ref's constructor is unavailable if
 the argument is not callable."

This reverts commit 4cae6228d129d4c4dfb156c043977bb6b5690031.

Breaks GCC build:
http://lab.llvm.org:8011/#/builders/8/builds/33/steps/6/logs/stdio
---
 llvm/include/llvm/ADT/STLExtras.h         | 13 +------------
 llvm/lib/AsmParser/LLParser.h             |  4 ++--
 llvm/lib/Bitcode/Reader/BitcodeReader.cpp |  4 +++-
 llvm/unittests/ADT/FunctionRefTest.cpp    | 11 -----------
 4 files changed, 6 insertions(+), 26 deletions(-)

diff --git a/llvm/include/llvm/ADT/STLExtras.h b/llvm/include/llvm/ADT/STLExtras.h
index b70a6f9..4be016b 100644
--- a/llvm/include/llvm/ADT/STLExtras.h
+++ b/llvm/include/llvm/ADT/STLExtras.h
@@ -186,27 +186,16 @@ class function_ref<Ret(Params...)> {
         std::forward<Params>(params)...);
   }
 
-  template <typename Callable,
-            typename Result =
-                typename std::result_of<Callable(Params...)>::type>
-  static constexpr bool IsCompatible =
-      std::is_void<Ret>::value || std::is_convertible<Result, Ret>::value;
-
 public:
   function_ref() = default;
   function_ref(std::nullptr_t) {}
 
   template <typename Callable>
-  // Only allow this constructor if the object is actually callable
-  // and returns the correct type.
   function_ref(
       Callable &&callable,
       std::enable_if_t<
-          // This is not the copy-constructor.
           !std::is_same<std::remove_cv_t<std::remove_reference_t<Callable>>,
-                        function_ref>::value &&
-          // Must be callable and return a suitable type.
-          IsCompatible<Callable>> * = nullptr)
+                        function_ref>::value> * = nullptr)
       : callback(callback_fn<typename std::remove_reference<Callable>::type>),
         callable(reinterpret_cast<intptr_t>(&callable)) {}
 
diff --git a/llvm/lib/AsmParser/LLParser.h b/llvm/lib/AsmParser/LLParser.h
index 5f581f0..a7fbcdd 100644
--- a/llvm/lib/AsmParser/LLParser.h
+++ b/llvm/lib/AsmParser/LLParser.h
@@ -166,8 +166,8 @@ namespace llvm {
         : Context(Context), Lex(F, SM, Err, Context), M(M), Index(Index),
           Slots(Slots), BlockAddressPFS(nullptr) {}
     bool Run(
-        bool UpgradeDebugInfo, DataLayoutCallbackTy DataLayoutCallback =
-                                   [](StringRef) { return None; });
+        bool UpgradeDebugInfo,
+        DataLayoutCallbackTy DataLayoutCallback = [](Module *) {});
 
     bool parseStandaloneConstantValue(Constant *&C, const SlotMapping *Slots);
 
diff --git a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
index 15ca3a5..4d69dd7 100644
--- a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -579,7 +579,9 @@ public:
   /// \returns true if an error occurred.
   Error parseBitcodeInto(
       Module *M, bool ShouldLazyLoadMetadata = false, bool IsImporting = false,
-      DataLayoutCallbackTy DataLayoutCallback = [](StringRef) { return None; });
+      DataLayoutCallbackTy DataLayoutCallback = [](std::string) {
+        return None;
+      });
 
   static uint64_t decodeSignRotatedValue(uint64_t V);
 
diff --git a/llvm/unittests/ADT/FunctionRefTest.cpp b/llvm/unittests/ADT/FunctionRefTest.cpp
index f084aa7..669b87d 100644
--- a/llvm/unittests/ADT/FunctionRefTest.cpp
+++ b/llvm/unittests/ADT/FunctionRefTest.cpp
@@ -48,15 +48,4 @@ TEST(FunctionRefTest, BadCopy) {
   ASSERT_EQ(1, X());
 }
 
-// Test that overloads on function_refs are resolved as expected.
-const char *returns(StringRef) { return "not a function"; }
-const char *returns(function_ref<double()> F) { return "number"; }
-const char *returns(function_ref<StringRef()> F) { return "string"; }
-
-TEST(FunctionRefTest, SFINAE) {
-  EXPECT_EQ("not a function", returns("boo!"));
-  EXPECT_EQ("number", returns([] { return 42; }));
-  EXPECT_EQ("string", returns([] { return "hello"; }));
-}
-
 } // namespace
-- 
2.7.4