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digitalmars.D.bugs - [Issue 12384] New: Improve optimization of nothrow code

https://d.puremagic.com/issues/show_bug.cgi?id=12384

           Summary: Improve optimization of nothrow code
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: bugzilla digitalmars.com


--- Comment #0 from Walter Bright <bugzilla digitalmars.com> 2014-03-16
16:48:55 PDT ---
Consider:

----------------------------
import core.stdc.stdlib;

void fun() nothrow;

struct B {
  int* p;
  size_t x;
}

size_t fun4(ref B a) {
   B b;
   scope (exit) free(b.p);
   fun();
   return b.x + a.x;
}
----------------------------

This current sets up an exception handler to call free(b.p), even though no
exceptions can be thrown. Instead, the code rewrite should be:

---------------------
size_t fun4(ref B a) {
   B b;
   fun();
   auto tmp = b.x + a.x;
   free(b.p);
   return tmp;
}
-----------------------

This will result in significant performance improvements. Currently, only one
such rewrite case is handled in TryFinallyStatement::semantic(). There's more
low hanging fruit, such as the return statement case above, that should be
handled there.

(scope-statements are rewritten as try-finally-statements.)

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Mar 16 2014