Because all that should be needed (on windows) is 
#define PERL_GET_CONTEXT TlsGetValue(PL_thr_key)
#define PERL_SET_CONTEXT(t) TlsSetValue(PL_thr_key, (t))

download

Quite why those calls are bracketed to preserve information from a previous error is strange.

What previous error have we ignored -- by continuing to this piece of code -- that we want to retain the extended error information for?

And what are we going to do with that retained information? And when?

You do realize your idea will break $^E?

Remember there is this questionable file that can steal your C lib away from you, win32/win32iop.h in perl.git.

errno is nearly useless on Windows since its so vague and rarely set compared to LastError/$^E. Side note, on a nytprof profiler in my experience, Win32::GetLastError() is 10 times faster than $^E. Perl does its best to always keep Win32's last error accurate to the last Win32 call you consciously made (CRT things, like malloc or free, or Kernel32 HeapAlloc (http://msdn.microsoft.com/en-us/library/windows/desktop/aa366597%28v=vs.85%29.aspx), should not and do not change LastError), otherwise a mortal sweeping at scope boundaries would make LastError absolutely useless in perl as it frees SVPVs and make it impossible to do many Win32-ish things. Sometimes I've had GetLastError be screwed up in Perl because a 
$obj = Win32::Foo->new("create me");
#new returned a blessed object
$obj = Win32::Foo->new("dont create me");
#new returned undef and LastError has failure code, DESTROY of "create
+ me" fires, changes LastError
if(! defined  $obj){
     #$^E happens to be ERROR_SUCCESS (it is actually undefined/random
+), programmer pounds head on keyboard screaming WHY ME!!!!
     die "creating obj failed ".($^E+0);
}

[download]
IMHO, LastError is a terrible design. Native API's NTSTATUS error code system is much better thought out (http://msdn.microsoft.com/en-us/library/cc231200%28v=prot.10%29) with positive signed numbers being informational non-errors, 0 being success with no information, and negative being errors.

In reply to Re^16: Perl 5 Optimizing Compiler, Part 4: LLVM Backend? by bulk88
in thread Perl 5 Optimizing Compiler, Part 4: LLVM Backend? by Will_the_Chill

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