[PATCH] Turn off uninitialized-use warnings for gcc in cmake build

[Edwin Vane]

  Vast simplification based on reviewer observation that although gcc
  won't complain about unsupported -Wno-* flags it *will* complain about
  unsupported -W flags. Instead of testing for -Wno-maybe-uninitialized we
  test for the positive.

  Someone should fix up the logic in autoconf/configure.ac the same way
  too.

Hi chandlerc, gribozavr, doug.gregor,

http://llvm-reviews.chandlerc.com/D353

CHANGE SINCE LAST DIFF
  http://llvm-reviews.chandlerc.com/D353?vs=835&id=842#toc

Files:
  cmake/config-ix.cmake
  cmake/modules/HandleLLVMOptions.cmake

Index: cmake/config-ix.cmake
===================================================================
--- cmake/config-ix.cmake
+++ cmake/config-ix.cmake
@@ -304,6 +304,24 @@
 
 check_cxx_compiler_flag("-Wno-variadic-macros" SUPPORTS_NO_VARIADIC_MACROS_FLAG)
 
+set(USE_NO_MAYBE_UNINITIALIZED 0)
+set(USE_NO_UNINITIALIZED 0)
+
+# Disable gcc's potentially uninitialized use analysis as it presents lots of
+# false positives.
+if (CMAKE_COMPILER_IS_GNUCXX)
+  check_cxx_compiler_flag("-Wmaybe-uninitialized" HAS_MAYBE_UNINITIALIZED)
+  if (HAS_MAYBE_UNINITIALIZED)
+    set(USE_NO_MAYBE_UNINITIALIZED 1)
+  else()
+    # Only recent versions of gcc make the distinction between -Wuninitialized
+    # and -Wmaybe-uninitialized. If -Wmaybe-uninitialized isn't supported, just
+    # turn off all uninitialized use warnings.
+    check_cxx_compiler_flag("-Wuninitialized" HAS_UNINITIALIZED)
+    set(USE_NO_UNINITIALIZED ${HAS_UNINITIALIZED})
+  endif()
+endif()
+
 include(GetHostTriple)
 get_host_triple(LLVM_HOST_TRIPLE)
 
Index: cmake/modules/HandleLLVMOptions.cmake
===================================================================
--- cmake/modules/HandleLLVMOptions.cmake
+++ cmake/modules/HandleLLVMOptions.cmake
@@ -178,6 +178,14 @@
 elseif( LLVM_COMPILER_IS_GCC_COMPATIBLE )
   if (LLVM_ENABLE_WARNINGS)
     add_llvm_definitions( -Wall -W -Wno-unused-parameter -Wwrite-strings )
+    # Turn off missing field initializer warnings for gcc to avoid noise from
+    # false positives with empty {}. Turn them on otherwise (they're off by
+    # default for clang).
+    if (CMAKE_COMPILER_IS_GNUCXX)
+      add_llvm_definitions( -Wno-missing-field-initializers )
+    else()
+      add_llvm_definitions( -Wmissing-field-initializers )
+    endif()
     if (LLVM_ENABLE_PEDANTIC)
       add_llvm_definitions( -pedantic -Wno-long-long )
     endif (LLVM_ENABLE_PEDANTIC)
@@ -189,6 +197,12 @@
     if( C_SUPPORTS_COVERED_SWITCH_DEFAULT_FLAG )
       set( CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wcovered-switch-default" )
     endif()
+    if (USE_NO_UNINITIALIZED)
+      set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-uninitialized")
+    endif()
+    if (USE_NO_MAYBE_UNINITIALIZED)
+      set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-maybe-uninitialized")
+    endif()
   endif (LLVM_ENABLE_WARNINGS)
   if (LLVM_ENABLE_WERROR)
     add_llvm_definitions( -Werror )
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