d: Don't generate code that throws exceptions when compiling with `-fno-exceptions'

The version flags for RTMI, RTTI, and exceptions was unconditionally
predefined.  These are now only predefined if the feature flag is
enabled.  It was noticed that there was no `-fexceptions' definition
inside d/lang.opt, so the detection of the exceptions option flag was
only partially working.  Once that was fixed, a few places in the
front-end implementation were found to fall fowl of `nothrow' rules,
these have been fixed upstream and backported here as well.

Reviewed-on: https://github.com/dlang/dmd/pull/15357
	     https://github.com/dlang/dmd/pull/15360

	PR d/110471

gcc/d/ChangeLog:

	* d-builtins.cc (d_init_versions): Predefine D_ModuleInfo,
	D_Exceptions, and D_TypeInfo only if feature is enabled.
	* lang.opt: Add -fexceptions.

gcc/testsuite/ChangeLog:

	* gdc.dg/pr110471a.d: New test.
	* gdc.dg/pr110471b.d: New test.
	* gdc.dg/pr110471c.d: New test.

(cherry picked from commit da108c75ad386b3f1f47abb2265296e4b61d578a)

gcc/d/d-builtins.cc

@@ -500,9 +500,12 @@ d_init_versions (void)
     VersionCondition::addPredefinedGlobalIdent ("D_BetterC");
   else
     {
-      VersionCondition::addPredefinedGlobalIdent ("D_ModuleInfo");
-      VersionCondition::addPredefinedGlobalIdent ("D_Exceptions");
-      VersionCondition::addPredefinedGlobalIdent ("D_TypeInfo");
+      if (global.params.useModuleInfo)
+       VersionCondition::addPredefinedGlobalIdent ("D_ModuleInfo");
+      if (global.params.useExceptions)
+       VersionCondition::addPredefinedGlobalIdent ("D_Exceptions");
+      if (global.params.useTypeInfo)
+       VersionCondition::addPredefinedGlobalIdent ("D_TypeInfo");
     }
 
   if (optimize)

gcc/d/dmd/root/array.d

@@ -574,7 +574,7 @@ unittest
 private template arraySortWrapper(T, alias fn)
 {
     pragma(mangle, "arraySortWrapper_" ~ T.mangleof ~ "_" ~ fn.mangleof)
-    extern(C) int arraySortWrapper(scope const void* e1, scope const void* e2) nothrow
+    extern(C) int arraySortWrapper(scope const void* e1, scope const void* e2)
     {
         return fn(cast(const(T*))e1, cast(const(T*))e2);
     }

gcc/d/dmd/semantic2.d

@@ -807,9 +807,8 @@ private void doGNUABITagSemantic(ref Expression e, ref Expression* lastTag)
     // but it's a concession to practicality.
     // Casts are unfortunately necessary as `implicitConvTo` is not
     // `const` (and nor is `StringExp`, by extension).
-    static int predicate(const scope Expression* e1, const scope Expression* e2) nothrow
+    static int predicate(const scope Expression* e1, const scope Expression* e2)
     {
-        scope(failure) assert(0, "An exception was thrown");
         return (cast(Expression*)e1).toStringExp().compare((cast(Expression*)e2).toStringExp());
     }
     ale.elements.sort!predicate;

gcc/d/dmd/semantic3.d

@@ -1420,7 +1420,7 @@ private extern(C++) final class Semantic3Visitor : Visitor
          * https://issues.dlang.org/show_bug.cgi?id=14246
          */
         AggregateDeclaration ad = ctor.isMemberDecl();
-        if (!ctor.fbody || !ad || !ad.fieldDtor || !global.params.dtorFields || global.params.betterC || ctor.type.toTypeFunction.isnothrow)
+        if (!ctor.fbody || !ad || !ad.fieldDtor || !global.params.dtorFields || !global.params.useExceptions || ctor.type.toTypeFunction.isnothrow)
             return visit(cast(FuncDeclaration)ctor);
 
         /* Generate:

gcc/d/lang.opt

@@ -291,6 +291,10 @@ fdump-d-original
 D
 Display the frontend AST after parsing and semantic passes.
 
+fexceptions
+D
+; Documented in common.opt
+
 fextern-std=
 D Joined RejectNegative Enum(extern_stdcpp) Var(flag_extern_stdcpp)
 -fextern-std=<standard>	Set C++ name mangling compatibility with <standard>.

gcc/testsuite/gdc.dg/pr110471a.d

@@ -0,0 +1,5 @@
+// https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110471
+// { dg-do compile }
+// { dg-options "-fno-exceptions" }
+version (D_Exceptions)
+    static assert(0);

gcc/testsuite/gdc.dg/pr110471b.d

@@ -0,0 +1,5 @@
+// https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110471
+// { dg-do compile }
+// { dg-options "-fno-moduleinfo" }
+version (D_ModuleInfo)
+    static assert(0);

gcc/testsuite/gdc.dg/pr110471c.d

@@ -0,0 +1,5 @@
+// https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110471
+// { dg-do compile }
+// { dg-options "-fno-rtti" }
+version (D_TypeInfo)
+    static assert(0);