patching MPICH preprocessors

and added a warning about a potential issue with v3.X MPICH compilers. Also added code warnings that MSVC does not support the `#warning` pragma (ridiculous!)

Author: TysonRayJones

quest/include/deprecated.h

@@ -30,15 +30,16 @@
 
 #if !defined(DISABLE_DEPRECATION_WARNINGS) || DISABLE_DEPRECATION_WARNINGS == 0
 
-    #warning \
-        "Deprecated functions have been included in compilation. The QuEST v3 API will be attemptedly \
-        automatically substituted for the v4 API, although some uses of the old API will still fail to \
-        compile. For example, access to v3 struct fields (e.g. 'ComplexMatrixN.real[0][0]') must be \
-        manually replaced with v4 struct fields (e.g. 'CompMatr.cpuElems[0][0]'), though new v4 functions \
-        make struct field access mostly redundant (e.g. via 'setCompMatr()'). Even when successfully \
-        compiling, use of the deprecated v3 functions is dangerous; these are not unit-tested, and the \
-        auto-porting to v4 may introduce new bugs. As such, you should only use this facility to help \
-        refactor your code to v4, and should absolutely not continue to use the old v3 API for simulation."
+    // #warning command is always recognised (deprecated API is not MSVC-compatible)
+    #warning "\
+Deprecated functions have been included in compilation. The QuEST v3 API will be attemptedly \
+automatically substituted for the v4 API, although some uses of the old API will still fail to \
+compile. For example, access to v3 struct fields (e.g. 'ComplexMatrixN.real[0][0]') must be \
+manually replaced with v4 struct fields (e.g. 'CompMatr.cpuElems[0][0]'), though new v4 functions \
+make struct field access mostly redundant (e.g. via 'setCompMatr()'). Even when successfully \
+compiling, use of the deprecated v3 functions is dangerous; these are not unit-tested, and the \
+auto-porting to v4 may introduce new bugs. As such, you should only use this facility to help \
+refactor your code to v4, and should absolutely not continue to use the old v3 API for simulation."
 
 #endif
 

quest/src/comm/comm_config.cpp

@@ -34,6 +34,7 @@
     #ifdef OPEN_MPI
         #include <mpi-ext.h>
 
+        // #warning command is always recognised (OpenMPI is not Windows compatible)
         #ifndef MPIX_CUDA_AWARE_SUPPORT
             #warning "Could not ascertain whether MPI is CUDA-aware, so we will assume it is not. This means inter-GPU communication will be slowly routed through the CPU/RAM."
         #elif !MPIX_CUDA_AWARE_SUPPORT
@@ -42,6 +43,8 @@
     #endif
 
     /// @todo check whether MPICH is CUDA-aware
+    /// beware MSVC cannot parse #warning, and
+    /// Intel MPI would crash (but not MSMPI?)
 
 #endif
 

quest/src/comm/comm_routines.cpp

@@ -101,45 +101,30 @@ qindex MAX_MESSAGE_LENGTH = powerOf2(28);
 
 #if COMPILE_MPI
 
-    // declare MPI type for qreal
-    #if   (FLOAT_PRECISION == 1)
-        #define MPI_QREAL MPI_FLOAT
-    #elif (FLOAT_PRECISION == 2)
-        #define MPI_QREAL MPI_DOUBLE
-    #elif (FLOAT_PRECISION == 4)
-        #define MPI_QREAL MPI_LONG_DOUBLE
+    // warn about strange behaviour on MPICH v3.X
+    #ifdef MPICH
+    #if MPI_VERSION < 4
+        // accursed Windows users get no warning (MSVC doesn't support #warning)
+        #ifndef _MSC_VER 
+        #warning "Using MPICH versions earlier than 4.0 may result in errors. Please run the distributed unit tests."
+        #endif
+    #endif
     #endif
 
-    /// @todo:
-    /// below is failing on ARCHER2 MPICH (depsite working on
-    /// other MPICH versions) because it defines the unsupported
-    /// preprocessors to be MPI_DATATYPE_NULL, as per:
-    /// https://trac.macports.org/ticket/71266. So below, we are
-    /// choosing to e.g. set MPI_QCOMP = MPI_CXX_DOUBLE_COMPLEX =
-    /// MPI_DATATYPE_NULL, which then fails at runtime. In lieu
-    /// of determining which MPICH versions do this, we presently
-    /// simply avoid the CXX macros altogether on MPICH.
-
-    // declare MPI type for qcomp, falling back to C types
-    // when the C++ type does not exist, as is the case for 
-    // MS MPI and other compilers at quad precision
-    #if   (FLOAT_PRECISION == 1) && defined(MPI_CXX_FLOAT_COMPLEX) && !defined(MPICH)
-        #define MPI_QCOMP MPI_CXX_FLOAT_COMPLEX
-    #elif (FLOAT_PRECISION == 1)
+    // declare MPI types for qreal and qcomp. We always use the 
+    // C macros, even when the deprecated CXX equivalents are 
+    // available, to maintain compatibility with modern MPICH
+    #if   (FLOAT_PRECISION == 1)
+        #define MPI_QREAL MPI_FLOAT
         #define MPI_QCOMP MPI_C_FLOAT_COMPLEX
-
-    #elif (FLOAT_PRECISION == 2) && defined(MPI_CXX_DOUBLE_COMPLEX) && !defined(MPICH)
-        #define MPI_QCOMP MPI_CXX_DOUBLE_COMPLEX
     #elif (FLOAT_PRECISION == 2)
+        #define MPI_QREAL MPI_DOUBLE
         #define MPI_QCOMP MPI_C_DOUBLE_COMPLEX
-
-    #elif (FLOAT_PRECISION == 4) && defined(MPI_CXX_LONG_DOUBLE_COMPLEX) && !defined(MPICH)
-        #define MPI_QCOMP MPI_CXX_LONG_DOUBLE_COMPLEX
     #elif (FLOAT_PRECISION == 4)
+        #define MPI_QREAL MPI_LONG_DOUBLE
         #define MPI_QCOMP MPI_C_LONG_DOUBLE_COMPLEX
-
     #else
-        #error "Something went horribly wrong in inferring the MPI type"
+        #error "Something went horribly wrong in inferring the MPI types"
     #endif
 
 #endif

quest/src/core/inliner.hpp

@@ -51,6 +51,8 @@
     #define INLINE inline __attribute__((always_inline))
 
 #else
+
+    // #warning command safe in non-MSVC compiler
     #warning "Could not ascertain compiler type in order to choose the correct inline attribute. Assuming GNU and proceeding..."
     #define INLINE inline __attribute__((always_inline))
 

quest/src/core/printer.cpp

@@ -155,6 +155,7 @@ int printer_getNumTrailingNewlines() {
 // fall-back to dangerous compiler-specific check (we know MSVC doesn't mangle)
 #elif ! defined _MSC_VER
 
+    // #warning command safe in non-MSVC compiler
     #warning "Attempting to include compiler-specific library <cxxabi.h>"
 
     #include <cxxabi.h>

tests/deprecated/test_main.cpp

@@ -27,7 +27,7 @@
 #include <stdexcept>
 
 
-/** Redefinition of QuEST_validation's invalidQuESTInputError function, called when a 
+/* Redefinition of QuEST_validation's invalidQuESTInputError function, called when a 
  * user passes an incorrect parameter (e.g. a negative qubit index). This is 
  * redefined here to, in lieu of printing and exiting, throw a C++ exception
  * which can be caught (and hence unit tested for) by Catch2