llvm dev - May 2013 - [LLVMdev] How to always generate epilogue code?

Hi!

I am still working on the Win64 EH code and now have a pretty usable 
result. (The MC part is already posted to llvm-commits, the other
part follows soon. If you are curious the whole patch is here: 
http://www.redstar.de/ldc/win64eh_all_20130524.diff.)

However, in one case I have a problem with LLVM being too smart. 
Consider the following D code:

void doIt()
{
     printf("doIt: start\n");
     try
     {
         printf("doIt: try\n");
         throw new Exception("Failure");
     }
     finally
     {
         printf("doIt: finally\n");
     }
     printf("doIt: end\n");
}

The code after the throw statement is unreachable. The last instruction 
of the finally block is a resume. LLVM now removes the last printf call 
and the epilogue code because it is all dead code. In fact the last 
instruction generated for this function is a call to the unwind_resume 
library function.

Unfortunately Windows 64bit requires the epilogue code to perform the 
stack unwinding. In this special case it is not dead code but another 
form of metadata. See here: 
http://msdn.microsoft.com/en-us/library/8ydc79k6.aspx.

Is there a simple way to always enforce the generation of the epilogue? 
E.g. can I mark the epilogue as always reachable?

Regards
Kai

Hi!

Nobody there who can give me a hint?

Regards
Kai

On 26.05.2013 13:22, Kai Nacke wrote:
> Hi!
>
> I am still working on the Win64 EH code and now have a pretty usable
> result. (The MC part is already posted to llvm-commits, the other
> part follows soon. If you are curious the whole patch is here:
> http://www.redstar.de/ldc/win64eh_all_20130524.diff.)
>
> However, in one case I have a problem with LLVM being too smart.
> Consider the following D code:
>
> void doIt()
> {
>      printf("doIt: start\n");
>      try
>      {
>          printf("doIt: try\n");
>          throw new Exception("Failure");
>      }
>      finally
>      {
>          printf("doIt: finally\n");
>      }
>      printf("doIt: end\n");
> }
>
> The code after the throw statement is unreachable. The last instruction
> of the finally block is a resume. LLVM now removes the last printf call
> and the epilogue code because it is all dead code. In fact the last
> instruction generated for this function is a call to the unwind_resume
> library function.
>
> Unfortunately Windows 64bit requires the epilogue code to perform the
> stack unwinding. In this special case it is not dead code but another
> form of metadata. See here:
> http://msdn.microsoft.com/en-us/library/8ydc79k6.aspx.
>
> Is there a simple way to always enforce the generation of the epilogue?
> E.g. can I mark the epilogue as always reachable?
>
> Regards
> Kai
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