From 7e58e5bb68cb058370b5015f576ee5507e56facc Mon Sep 17 00:00:00 2001 From: Brad King Date: Thu, 2 Aug 2012 11:53:25 -0400 Subject: Prefer generic system compilers by default for C, C++, and Fortran Teach CMake to prefer the system default compiler automatically when no compiler is specified. By default use "cc" for C, "CC" for C++, and "f95" for Fortran. Load a new Platform/-.cmake module to allow each platform to specify for each language its system compiler name(s) and/or exclude certain names. Create Platform/(CYGWIN|Darwin|Linux|Windows)-CXX.cmake modules to specify "c++" as the system C++ compiler name for these platforms. On systems that use case-insensitive filesystems exclude C++ compiler names that are distinguished from C compiler names only by case. This will change the default compiler selection for existing build scripts that do not specify a compiler when run on machines with separate system and GNU compilers both installed in the PATH. We do not make this change in default behavior lightly. However: (1) If a given build really needs specific compilers one should specify them explicitly e.g. by setting CC, CXX, and FC in the environment. (2) The motivating case is to prefer the system Clang on newer OS X systems over the older GNU compilers typically also installed. On such systems the names "cc" and "c++" link to Clang. This is the first platform known to CMake on which "c++" is not a GNU compiler. The old behavior selected "gcc" for C and "c++" C++ and therefore chooses GNU for C and Clang for C++ by default. The new behavior selects GNU or Clang consistently for both languages on older or newer OS X systems, respectively. (3) Other than the motivating OS X case the conditions under which the behavior changes do not tend to exist in default OS installations. They typically occur only on non-GNU systems with manually-installed GNU compilers. (4) The consequences of the new behavior are not dire. At worst the project fails to compile with the system compiler when it previously worked with the non-system GNU compiler. Such failure is easy to work around (see #1). In short this change creates a more sensible default behavior everywhere and fixes poor default behavior on a widely-used platform at the cost of a modest change in behavior in less-common conditions. --- Modules/CMakeDetermineASMCompiler.cmake | 5 +++-- Modules/CMakeDetermineCCompiler.cmake | 8 +++++++- Modules/CMakeDetermineCXXCompiler.cmake | 8 +++++++- Modules/CMakeDetermineCompiler.cmake | 6 ++++++ Modules/CMakeDetermineFortranCompiler.cmake | 4 ++++ Modules/Platform/CYGWIN-CXX.cmake | 7 +++++++ Modules/Platform/Darwin-CXX.cmake | 7 +++++++ Modules/Platform/Linux-CXX.cmake | 3 +++ Modules/Platform/Windows-CXX.cmake | 7 +++++++ 9 files changed, 51 insertions(+), 4 deletions(-) create mode 100644 Modules/Platform/CYGWIN-CXX.cmake create mode 100644 Modules/Platform/Darwin-CXX.cmake create mode 100644 Modules/Platform/Linux-CXX.cmake create mode 100644 Modules/Platform/Windows-CXX.cmake diff --git a/Modules/CMakeDetermineASMCompiler.cmake b/Modules/CMakeDetermineASMCompiler.cmake index a56020fb67..7da6ac04aa 100644 --- a/Modules/CMakeDetermineASMCompiler.cmake +++ b/Modules/CMakeDetermineASMCompiler.cmake @@ -33,8 +33,9 @@ IF(NOT CMAKE_ASM${ASM_DIALECT}_COMPILER) SET(CMAKE_ASM_COMPILER_ID "${CMAKE_CXX_COMPILER_ID}") ELSE() # List all default C and CXX compilers - SET(CMAKE_ASM${ASM_DIALECT}_COMPILER_LIST ${_CMAKE_TOOLCHAIN_PREFIX}gcc ${_CMAKE_TOOLCHAIN_PREFIX}cc cl bcc xlc - ${_CMAKE_TOOLCHAIN_PREFIX}c++ ${_CMAKE_TOOLCHAIN_PREFIX}g++ CC aCC cl bcc xlC) + SET(CMAKE_ASM${ASM_DIALECT}_COMPILER_LIST + ${_CMAKE_TOOLCHAIN_PREFIX}cc ${_CMAKE_TOOLCHAIN_PREFIX}gcc cl bcc xlc + CC ${_CMAKE_TOOLCHAIN_PREFIX}c++ ${_CMAKE_TOOLCHAIN_PREFIX}g++ aCC cl bcc xlC) ENDIF() ENDIF() ELSE() # some specific assembler "dialect" diff --git a/Modules/CMakeDetermineCCompiler.cmake b/Modules/CMakeDetermineCCompiler.cmake index 9ebf0b3957..3ce968c02d 100644 --- a/Modules/CMakeDetermineCCompiler.cmake +++ b/Modules/CMakeDetermineCCompiler.cmake @@ -33,6 +33,12 @@ INCLUDE(${CMAKE_ROOT}/Modules/CMakeDetermineCompiler.cmake) +# Load system-specific compiler preferences for this language. +INCLUDE(Platform/${CMAKE_SYSTEM_NAME}-C OPTIONAL) +IF(NOT CMAKE_C_COMPILER_NAMES) + SET(CMAKE_C_COMPILER_NAMES cc) +ENDIF() + IF(NOT CMAKE_C_COMPILER) SET(CMAKE_C_COMPILER_INIT NOTFOUND) @@ -56,7 +62,7 @@ IF(NOT CMAKE_C_COMPILER) # finally list compilers to try IF(NOT CMAKE_C_COMPILER_INIT) - SET(CMAKE_C_COMPILER_LIST ${_CMAKE_TOOLCHAIN_PREFIX}gcc ${_CMAKE_TOOLCHAIN_PREFIX}cc cl bcc xlc clang) + SET(CMAKE_C_COMPILER_LIST ${_CMAKE_TOOLCHAIN_PREFIX}cc ${_CMAKE_TOOLCHAIN_PREFIX}gcc cl bcc xlc clang) ENDIF() _cmake_find_compiler(C) diff --git a/Modules/CMakeDetermineCXXCompiler.cmake b/Modules/CMakeDetermineCXXCompiler.cmake index 43b44acd92..0116d341ab 100644 --- a/Modules/CMakeDetermineCXXCompiler.cmake +++ b/Modules/CMakeDetermineCXXCompiler.cmake @@ -32,6 +32,12 @@ INCLUDE(${CMAKE_ROOT}/Modules/CMakeDetermineCompiler.cmake) +# Load system-specific compiler preferences for this language. +INCLUDE(Platform/${CMAKE_SYSTEM_NAME}-CXX OPTIONAL) +IF(NOT CMAKE_CXX_COMPILER_NAMES) + SET(CMAKE_CXX_COMPILER_NAMES CC) +ENDIF() + IF(NOT CMAKE_CXX_COMPILER) SET(CMAKE_CXX_COMPILER_INIT NOTFOUND) @@ -55,7 +61,7 @@ IF(NOT CMAKE_CXX_COMPILER) # finally list compilers to try IF(NOT CMAKE_CXX_COMPILER_INIT) - SET(CMAKE_CXX_COMPILER_LIST ${_CMAKE_TOOLCHAIN_PREFIX}c++ ${_CMAKE_TOOLCHAIN_PREFIX}g++ CC aCC cl bcc xlC clang++) + SET(CMAKE_CXX_COMPILER_LIST CC ${_CMAKE_TOOLCHAIN_PREFIX}c++ ${_CMAKE_TOOLCHAIN_PREFIX}g++ aCC cl bcc xlC clang++) ENDIF() _cmake_find_compiler(CXX) diff --git a/Modules/CMakeDetermineCompiler.cmake b/Modules/CMakeDetermineCompiler.cmake index 55d554bdcf..2d12c07578 100644 --- a/Modules/CMakeDetermineCompiler.cmake +++ b/Modules/CMakeDetermineCompiler.cmake @@ -29,10 +29,16 @@ macro(_cmake_find_compiler lang) list(APPEND CMAKE_${lang}_COMPILER_LIST ${_${lang}_COMPILER_NAMES_${CMAKE_${l}_COMPILER_ID}}) endforeach() + # Prefer vendors based on the platform. + list(APPEND CMAKE_${lang}_COMPILER_LIST ${CMAKE_${lang}_COMPILER_NAMES}) # Append the rest of the list and remove duplicates. list(APPEND CMAKE_${lang}_COMPILER_LIST ${_${lang}_COMPILER_LIST}) unset(_${lang}_COMPILER_LIST) list(REMOVE_DUPLICATES CMAKE_${lang}_COMPILER_LIST) + if(CMAKE_${lang}_COMPILER_EXCLUDE) + list(REMOVE_ITEM CMAKE_${lang}_COMPILER_LIST + ${CMAKE_${lang}_COMPILER_EXCLUDE}) + endif() endif() # Look for directories containing compilers of reference languages. diff --git a/Modules/CMakeDetermineFortranCompiler.cmake b/Modules/CMakeDetermineFortranCompiler.cmake index 6d6990e6f4..45033c2a39 100644 --- a/Modules/CMakeDetermineFortranCompiler.cmake +++ b/Modules/CMakeDetermineFortranCompiler.cmake @@ -20,6 +20,10 @@ # as a default compiler INCLUDE(${CMAKE_ROOT}/Modules/CMakeDetermineCompiler.cmake) +INCLUDE(Platform/${CMAKE_SYSTEM_NAME}-Fortran OPTIONAL) +IF(NOT CMAKE_Fortran_COMPILER_NAMES) + SET(CMAKE_Fortran_COMPILER_NAMES f95) +ENDIF() IF(NOT CMAKE_Fortran_COMPILER) # prefer the environment variable CC diff --git a/Modules/Platform/CYGWIN-CXX.cmake b/Modules/Platform/CYGWIN-CXX.cmake new file mode 100644 index 0000000000..bf37f79030 --- /dev/null +++ b/Modules/Platform/CYGWIN-CXX.cmake @@ -0,0 +1,7 @@ +if(NOT CMAKE_CXX_COMPILER_NAMES) + set(CMAKE_CXX_COMPILER_NAMES c++) +endif() + +# Exclude C++ compilers differing from C compiler only by case +# because this platform may have a case-insensitive filesystem. +set(CMAKE_CXX_COMPILER_EXCLUDE CC aCC xlC) diff --git a/Modules/Platform/Darwin-CXX.cmake b/Modules/Platform/Darwin-CXX.cmake new file mode 100644 index 0000000000..bf37f79030 --- /dev/null +++ b/Modules/Platform/Darwin-CXX.cmake @@ -0,0 +1,7 @@ +if(NOT CMAKE_CXX_COMPILER_NAMES) + set(CMAKE_CXX_COMPILER_NAMES c++) +endif() + +# Exclude C++ compilers differing from C compiler only by case +# because this platform may have a case-insensitive filesystem. +set(CMAKE_CXX_COMPILER_EXCLUDE CC aCC xlC) diff --git a/Modules/Platform/Linux-CXX.cmake b/Modules/Platform/Linux-CXX.cmake new file mode 100644 index 0000000000..b594daeb0b --- /dev/null +++ b/Modules/Platform/Linux-CXX.cmake @@ -0,0 +1,3 @@ +if(NOT CMAKE_CXX_COMPILER_NAMES) + set(CMAKE_CXX_COMPILER_NAMES c++) +endif() diff --git a/Modules/Platform/Windows-CXX.cmake b/Modules/Platform/Windows-CXX.cmake new file mode 100644 index 0000000000..bf37f79030 --- /dev/null +++ b/Modules/Platform/Windows-CXX.cmake @@ -0,0 +1,7 @@ +if(NOT CMAKE_CXX_COMPILER_NAMES) + set(CMAKE_CXX_COMPILER_NAMES c++) +endif() + +# Exclude C++ compilers differing from C compiler only by case +# because this platform may have a case-insensitive filesystem. +set(CMAKE_CXX_COMPILER_EXCLUDE CC aCC xlC) -- cgit v1.2.1