[flang][msvc] Do not use gcc/clang command line options for msvc.

[Meinersbur]

Summary

The command line options -Wno-error and -Wno-unused-parameter are specific to gcc/clang, do not use them when compiling with other compilers.

This patch is part of the series to make flang compilable with MS Visual Studio.

[isuruf]

What's the reason for keeping these? IMO, the lines should be removed and let FLANG_ENABLE_WERROR cmake option add it if a developer needs it.

[Meinersbur]

Some developers build with -Werror and removing them entirely would break their build since these components seem to have warnings in them. There were lengthy discussions about the point of -Werror already (see D78306, D81695), which this patch is not about, just making it msvc-compatible.

[klausler]

In D85355#2199935, @Meinersbur wrote:

Some developers build with -Werror and removing them entirely would break their build since these components seem to have warnings in them. There were lengthy discussions about the point of -Werror already (see D78306, D81695), which this patch is not about, just making it msvc-compatible.

We always built with -Werror before we contributed f18 to llvm, and still do so in-house for the discipline it enforces, but gcc's warning about unused function arguments produced false messages in the case of templatized code (esp. with constexpr) that are not practical to work around, so that warning is explicitly disabled.

[tskeith]

In D85355#2200014, @klausler wrote:

In D85355#2199935, @Meinersbur wrote:

Some developers build with -Werror and removing them entirely would break their build since these components seem to have warnings in them. There were lengthy discussions about the point of -Werror already (see D78306, D81695), which this patch is not about, just making it msvc-compatible.

We always built with -Werror before we contributed f18 to llvm, and still do so in-house for the discipline it enforces, but gcc's warning about unused function arguments produced false messages in the case of templatized code (esp. with constexpr) that are not practical to work around, so that warning is explicitly disabled.

I removed the setting of CMAKE_CXX_FLAGS and couldn't find a version of GCC that failed. Can we just get rid of this? @schweitz?

[tskeith]

I've created https://reviews.llvm.org/D85465 to remove these options completely.

flang/lib/Lower/CMakeLists.txt

+if (LLVM_COMPILER_IS_GCC_COMPATIBLE)
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-error -Wno-unused-parameter")
+endif ()
 get_property(dialect_libs GLOBAL PROPERTY MLIR_DIALECT_LIBS)
 
 add_flang_library(FortranLower
   CharacterExpr.cpp
   CharacterRuntime.cpp
   Coarray.cpp
   ComplexExpr.cpp
   ConvertType.cpp

flang/lib/Optimizer/CMakeLists.txt

+if (LLVM_COMPILER_IS_GCC_COMPATIBLE)
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-unused-parameter -Wno-error")
+endif ()
 get_property(dialect_libs GLOBAL PROPERTY MLIR_DIALECT_LIBS)
 
 add_flang_library(FIROptimizer
   Dialect/FIRAttr.cpp
   Dialect/FIRDialect.cpp
   Dialect/FIROps.cpp
   Dialect/FIRType.cpp