[Flang][Runtime] Handle missing definitions in <cfenv> (llvm#101242)

According to the C99 standard, <fenv.h> may not define FE_INVALID and
the likes. Even if C++11 mandate them, musl and emscripten don't provide
them, so handle that case.

Author: serge-sans-paille

flang/runtime/edit-input.cpp

@@ -507,18 +507,29 @@ static RT_API_ATTRS void RaiseFPExceptions(
 #define RAISE std::feraiseexcept
 #endif
 #endif // !defined(RT_DEVICE_COMPILATION)
+
+// Some environment (e.g. emscripten, musl) don't define FE_OVERFLOW as allowed
+// by c99 (but not c++11) :-/
+#if defined(FE_OVERFLOW) || defined(RT_DEVICE_COMPILATION)
   if (flags & decimal::ConversionResultFlags::Overflow) {
     RAISE(FE_OVERFLOW);
   }
+#endif
+#if defined(FE_UNDERFLOW) || defined(RT_DEVICE_COMPILATION)
   if (flags & decimal::ConversionResultFlags::Underflow) {
     RAISE(FE_UNDERFLOW);
   }
+#endif
+#if defined(FE_INEXACT) || defined(RT_DEVICE_COMPILATION)
   if (flags & decimal::ConversionResultFlags::Inexact) {
     RAISE(FE_INEXACT);
   }
+#endif
+#if defined(FE_INVALID) || defined(RT_DEVICE_COMPILATION)
   if (flags & decimal::ConversionResultFlags::Invalid) {
     RAISE(FE_INVALID);
   }
+#endif
 #undef RAISE
 }
 

flang/runtime/exceptions.cpp

@@ -12,9 +12,26 @@
 #include "terminator.h"
 #include <cfenv>
 
+// When not supported, these macro are undefined in cfenv.h,
+// set them to zero in that case.
+#ifndef FE_INVALID
+#define FE_INVALID 0
+#endif
 #ifndef __FE_DENORM
 #define __FE_DENORM 0 // denorm is nonstandard
 #endif
+#ifndef FE_DIVBYZERO
+#define FE_DIVBYZERO 0
+#endif
+#ifndef FE_OVERFLOW
+#define FE_OVERFLOW 0
+#endif
+#ifndef FE_UNDERFLOW
+#define FE_UNDERFLOW 0
+#endif
+#ifndef FE_INEXACT
+#define FE_INEXACT 0
+#endif
 
 namespace Fortran::runtime {
 
@@ -45,7 +62,12 @@ uint32_t RTNAME(MapException)(uint32_t excepts) {
   if (excepts == 0 || excepts >= mapSize) {
     terminator.Crash("Invalid excepts value: %d", excepts);
   }
-  return map[excepts];
+  uint32_t except_value = map[excepts];
+  if (except_value == 0) {
+    terminator.Crash(
+        "Excepts value %d not supported by flang runtime", excepts);
+  }
+  return except_value;
 }
 
 // Verify that the size of ieee_modes_type and ieee_status_type objects from

flang/runtime/stop.cpp

@@ -26,21 +26,31 @@ static void DescribeIEEESignaledExceptions() {
 #endif
   if (excepts) {
     std::fputs("IEEE arithmetic exceptions signaled:", stderr);
+#ifdef FE_DIVBYZERO
     if (excepts & FE_DIVBYZERO) {
       std::fputs(" DIVBYZERO", stderr);
     }
+#endif
+#ifdef FE_INEXACT
     if (excepts & FE_INEXACT) {
       std::fputs(" INEXACT", stderr);
     }
+#endif
+#ifdef FE_INVALID
     if (excepts & FE_INVALID) {
       std::fputs(" INVALID", stderr);
     }
+#endif
+#ifdef FE_OVERFLOW
     if (excepts & FE_OVERFLOW) {
       std::fputs(" OVERFLOW", stderr);
     }
+#endif
+#ifdef FE_UNDERFLOW
     if (excepts & FE_UNDERFLOW) {
       std::fputs(" UNDERFLOW", stderr);
     }
+#endif
     std::fputc('\n', stderr);
   }
 }