misc: Updates for gcc7.2 for x86

GCC 7.2 is much stricter than previous GCC versions. The following changes
are needed:

* There is now a warning if there is an implicit fallthrough between two
  case statments. C++17 adds the [[fallthrough]]; declaration. However,
  to support non C++17 standards (i.e., C++11), we use M5_FALLTHROUGH.
  M5_FALLTHROUGH checks for [[fallthrough]] compliant C++17 compiler and
  if that doesn't exist, it defaults to nothing (no older compilers
  generate warnings).
* The above resulted in a couple of bugs that were found. This is noted
  in the review request on gerrit.
* throw() for dynamic exception specification is deprecated
* There were a couple of new uninitialized variable warnings
* Can no longer perform bitwise operations on a bool.
* Must now include <functional> for std::function
* Compiler bug for void* lambda. Changed to auto as work around. See
  https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82878

Change-Id: I5d4c782a4e133fa4cdb119e35d9aff68c6e2958e
Signed-off-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-on: https://gem5-review.googlesource.com/5802
Reviewed-by: Gabe Black <gabeblack@google.com>

1 files changed, 14 insertions, 0 deletions

diff --git a/src/base/compiler.hh b/src/base/compiler.hh
index 2fdd323b9..6920dad10 100644
--- a/src/base/compiler.hh
+++ b/src/base/compiler.hh
@@ -63,6 +63,20 @@
 #  define M5_CLASS_VAR_USED
 #endif
 
+// This can be removed once all compilers support C++17
+#if defined __has_cpp_attribute
+    // Note: We must separate this if statement because GCC < 5.0 doesn't
+    //       support the function-like syntax in #if statements.
+    #if __has_cpp_attribute(fallthrough)
+        #define M5_FALLTHROUGH [[fallthrough]]
+    #else
+        #define M5_FALLTHROUGH
+    #endif
+#else
+    // Unsupported (and no warning) on GCC < 7.
+    #define M5_FALLTHROUGH
+#endif
+
 // std::make_unique redefined for C++11 compilers
 namespace m5
 {