Avoid bad compile time scaling of test registration with optimizations

GCC is especially bad, as it had quadratic scaling in the number of
registered test cases in a TU, but Clang also scaled superlinearly, and
this commit fixes both.

AIUI:
1) Each `TEST_CASE` creates a separate global fragment to handle creating
   the `unique_ptr<ITestInvoker>`, moving the instance into AutoReg,
   destroying the old instance, etc, etc.
2) With optimizations enabled, the compiler merges all these global
   fragments into one big global fragment.
3) Then the compiler runs various optimizations passes on this new global
   fragment.
4) Because some of the passes scale superlinearly, the compilation times
   scale superlinearly in the number of `TEST_CASE` in a translation unit.

For bonus point, no optimization actually happens.

This commit fixes the problem (for non-LTO builds) by adding new `AutoReg`
constructor, one that takes the function pointer raw, instead of wrapped
in `ITestInvoker`. By delaying the construction of the `ITestInvoker`
into the outlined constructor, we no longer create big global fragments
for the compiler to optimize.

3 files changed, 29 insertions, 5 deletions

diff --git a/src/catch2/internal/catch_template_test_registry.hpp b/src/catch2/internal/catch_template_test_registry.hpp
index ed25251a..47da95bb 100644
--- a/src/catch2/internal/catch_template_test_registry.hpp
+++ b/src/catch2/internal/catch_template_test_registry.hpp
@@ -136,7 +136,7 @@
                     constexpr char const* tmpl_types[] = {CATCH_REC_LIST(INTERNAL_CATCH_STRINGIZE_WITHOUT_PARENS, INTERNAL_CATCH_REMOVE_PARENS(TmplTypes))};\
                     constexpr char const* types_list[] = {CATCH_REC_LIST(INTERNAL_CATCH_STRINGIZE_WITHOUT_PARENS, INTERNAL_CATCH_REMOVE_PARENS(TypesList))};\
                     constexpr auto num_types = sizeof(types_list) / sizeof(types_list[0]);\
-                    (void)expander{(Catch::AutoReg( Catch::makeTestInvoker( &TestFuncName<Types> ), CATCH_INTERNAL_LINEINFO, Catch::StringRef(), Catch::NameAndTags{ Name " - " + std::string(tmpl_types[index / num_types]) + '<' + types_list[index % num_types] + '>', Tags } ), index++)... };/* NOLINT */\
+                    (void)expander{(Catch::AutoReg( &TestFuncName<Types>, CATCH_INTERNAL_LINEINFO, Catch::StringRef(), Catch::NameAndTags{ Name " - " + std::string(tmpl_types[index / num_types]) + '<' + types_list[index % num_types] + '>', Tags } ), index++)... };/* NOLINT */\
                 }                                                     \
             };                                                        \
             static const int INTERNAL_CATCH_UNIQUE_NAME( globalRegistrar ) = [](){ \
@@ -182,7 +182,7 @@
             void reg_tests() {                                          \
                 size_t index = 0;                                    \
                 using expander = size_t[];                           \
-                (void)expander{(Catch::AutoReg( Catch::makeTestInvoker( &TestFunc<Types> ), CATCH_INTERNAL_LINEINFO, Catch::StringRef(), Catch::NameAndTags{ Name " - " INTERNAL_CATCH_STRINGIZE(TmplList) " - " + std::to_string(index), Tags } ), index++)... };/* NOLINT */\
+                (void)expander{(Catch::AutoReg( &TestFunc<Types>, CATCH_INTERNAL_LINEINFO, Catch::StringRef(), Catch::NameAndTags{ Name " - " INTERNAL_CATCH_STRINGIZE(TmplList) " - " + std::to_string(index), Tags } ), index++)... };/* NOLINT */\
             }                                                     \
         };\
         static const int INTERNAL_CATCH_UNIQUE_NAME( globalRegistrar ) = [](){ \
diff --git a/src/catch2/internal/catch_test_registry.cpp b/src/catch2/internal/catch_test_registry.cpp
index d017c50e..3a2f006a 100644
--- a/src/catch2/internal/catch_test_registry.cpp
+++ b/src/catch2/internal/catch_test_registry.cpp
@@ -66,6 +66,15 @@ namespace Catch {
         return Detail::make_unique<TestInvokerAsFunction>( testAsFunction );
     }
 
+    AutoReg::AutoReg( void ( *testAsFunction )(),
+                      SourceLineInfo const& lineInfo,
+                      StringRef classOrMethod,
+                      NameAndTags const& nameAndTags ) noexcept:
+        AutoReg( makeTestInvoker( testAsFunction ),
+                 lineInfo,
+                 classOrMethod,
+                 nameAndTags ) {}
+
     AutoReg::AutoReg( Detail::unique_ptr<ITestInvoker> invoker, SourceLineInfo const& lineInfo, StringRef classOrMethod, NameAndTags const& nameAndTags ) noexcept {
         CATCH_TRY {
             getMutableRegistryHub()
diff --git a/src/catch2/internal/catch_test_registry.hpp b/src/catch2/internal/catch_test_registry.hpp
index 213b2bdc..e81c728d 100644
--- a/src/catch2/internal/catch_test_registry.hpp
+++ b/src/catch2/internal/catch_test_registry.hpp
@@ -85,7 +85,22 @@ struct NameAndTags {
 };
 
 struct AutoReg : Detail::NonCopyable {
-    AutoReg( Detail::unique_ptr<ITestInvoker> invoker, SourceLineInfo const& lineInfo, StringRef classOrMethod, NameAndTags const& nameAndTags ) noexcept;
+    AutoReg( Detail::unique_ptr<ITestInvoker> invoker,
+             SourceLineInfo const& lineInfo,
+             StringRef classOrMethod,
+             NameAndTags const& nameAndTags ) noexcept;
+
+    /**
+     * Overload that takes the simple function pointer directly.
+     *
+     * Useful to keep compilation costs low; the unique_ptr overload
+     * combined with `makeTestInvoker` causes quadratic compilation times
+     * with GCC + optimizations (and super-linear with Clang + optims).
+     */
+    AutoReg( void ( *testAsFunction )(),
+             SourceLineInfo const& lineInfo,
+             StringRef classOrMethod,
+             NameAndTags const& nameAndTags ) noexcept;
 };
 
 } // end namespace Catch
@@ -111,7 +126,7 @@ struct AutoReg : Detail::NonCopyable {
         CATCH_INTERNAL_START_WARNINGS_SUPPRESSION \
         CATCH_INTERNAL_SUPPRESS_GLOBALS_WARNINGS \
         CATCH_INTERNAL_SUPPRESS_UNUSED_VARIABLE_WARNINGS \
-        namespace{ const Catch::AutoReg INTERNAL_CATCH_UNIQUE_NAME( autoRegistrar )( Catch::makeTestInvoker( &TestName ), CATCH_INTERNAL_LINEINFO, Catch::StringRef(), Catch::NameAndTags{ __VA_ARGS__ } ); } /* NOLINT */ \
+        namespace{ const Catch::AutoReg INTERNAL_CATCH_UNIQUE_NAME( autoRegistrar )( &TestName, CATCH_INTERNAL_LINEINFO, Catch::StringRef(), Catch::NameAndTags{ __VA_ARGS__ } ); } /* NOLINT */ \
         CATCH_INTERNAL_STOP_WARNINGS_SUPPRESSION \
         static void TestName()
     #define INTERNAL_CATCH_TESTCASE( ... ) \
@@ -214,7 +229,7 @@ static int catchInternalSectionHint = 0;
             CATCH_INTERNAL_START_WARNINGS_SUPPRESSION \
             CATCH_INTERNAL_SUPPRESS_GLOBALS_WARNINGS \
             CATCH_INTERNAL_SUPPRESS_UNUSED_VARIABLE_WARNINGS \
-            Catch::AutoReg INTERNAL_CATCH_UNIQUE_NAME( autoRegistrar )( Catch::makeTestInvoker( Function ), CATCH_INTERNAL_LINEINFO, Catch::StringRef(), Catch::NameAndTags{ __VA_ARGS__ } ); /* NOLINT */ \
+            Catch::AutoReg INTERNAL_CATCH_UNIQUE_NAME( autoRegistrar )( Function, CATCH_INTERNAL_LINEINFO, Catch::StringRef(), Catch::NameAndTags{ __VA_ARGS__ } ); /* NOLINT */ \
             CATCH_INTERNAL_STOP_WARNINGS_SUPPRESSION \
         } while(false)