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Avoid copying const string constants to the stack. #674

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Avoid copying const string constants to the stack. #674

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2 changes: 1 addition & 1 deletion objcgen/methodhelper.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -74,7 +74,7 @@ public void WriteMethodLookup ()
implementation.Indent++;
implementation.WriteLine ($"__method = mono_get_method (__{AssemblySafeName}_image, 0x{MetadataToken:X8}, {ObjCTypeName}_class);");
implementation.WriteLineUnindented ("#else");
implementation.WriteLine ($"const char __method_name [] = \"{ManagedTypeName}:{MonoSignature}\";");
implementation.WriteLine ($"static const char __method_name [] = \"{ManagedTypeName}:{MonoSignature}\";");
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Will this generate the same native code as if the string constant had been passed directly to the method call?

i.e.:

implementation.WriteLine ($"__method = mono_embeddinator_lookup_method (\"{ManagedTypeName}:{MonoSignature}\", {ObjCTypeName}_class);");

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Another way is to pass the literal directly.
There are tradeoffs either way.
With msvc:
Literals can be writable or not, depending on version/flags.
Literals can be single-instanced or not, depending on version/flags.
static const will be not writable and not single-instanced.
Ideal is readonly and single instanced.
Non-static const at least with msvc will copy to stack.
Though I have seen clang optimize similar, kinda surprising.
Perhaps literals w/o temporary are best.
Sometimes people will also assign the literal to a pointer.
That is a wasted assignment but only of a pointer, so minor.

implementation.WriteLine ($"__method = mono_embeddinator_lookup_method (__method_name, {ObjCTypeName}_class);");
implementation.Indent--;
implementation.WriteLineUnindented ("#endif");
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4 changes: 2 additions & 2 deletions objcgen/objcgenerator.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -864,7 +864,7 @@ protected void Generate (ProcessedFieldInfo field)
implementation.WriteLineUnindented ("#if TOKENLOOKUP");
implementation.WriteLine ($"__field = mono_class_get_field ({managed_type_name}_class, 0x{fi.MetadataToken:X8});");
implementation.WriteLineUnindented ("#else");
implementation.WriteLine ($"const char __field_name [] = \"{fi.Name}\";");
implementation.WriteLine ($"static const char __field_name [] = \"{fi.Name}\";");
implementation.WriteLine ($"__field = mono_class_get_field_from_name ({managed_type_name}_class, __field_name);");
implementation.WriteLineUnindented ("#endif");
implementation.Indent--;
Expand Down Expand Up @@ -898,7 +898,7 @@ protected void Generate (ProcessedFieldInfo field)
implementation.WriteLineUnindented ("#if TOKENLOOKUP");
implementation.WriteLine ($"__field = mono_class_get_field ({managed_type_name}_class, 0x{fi.MetadataToken:X8});");
implementation.WriteLineUnindented ("#else");
implementation.WriteLine ($"const char __field_name [] = \"{fi.Name}\";");
implementation.WriteLine ($"static const char __field_name [] = \"{fi.Name}\";");
implementation.WriteLine ($"__field = mono_class_get_field_from_name ({managed_type_name}_class, __field_name);");
implementation.WriteLineUnindented ("#endif");
implementation.Indent--;
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