JumpThreading and @llvm.dbg.declare()

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#1

Hi!

I have a small issue with the JumpThreading pass (in opt). As described in the code (JumpThreading.cpp), the pass may if certain criteria are fulfilled duplicate the content of a block. If the duplicated block contain a call to @llvm.dbg.declare() you will end up with invalid code as the intrinsic @llvm.dbg.declare() only should occur once for each variable.

I think the JumpThreading pass should lower all llvm.dbg.declare() into llvm.dbg.value() the same way as the instcombine pass do (see InstructionCombining.cpp):

   // Lower dbg.declare intrinsics otherwise their value may be clobbered
   // by instcombiner.
   bool DbgDeclaresChanged = LowerDbgDeclare(F);

Do you agree? Ok to commit?

Regards
/ Karl-Johan Karlsson

#2

Did you forget to attach a patch? A patch with a test case showing the
problem you're describing would be great.

Also, patches should generally be sent to the llvm-commits list, not llvmdev.

Thanks,
Hans

#3

I have a small issue with the JumpThreading pass (in opt). As described in
the code (JumpThreading.cpp), the pass may if certain criteria are fulfilled
duplicate the content of a block. If the duplicated block contain a call to
@llvm.dbg.declare() you will end up with invalid code as the intrinsic
@llvm.dbg.declare() only should occur once for each variable.

I think the JumpThreading pass should lower all llvm.dbg.declare() into
llvm.dbg.value() the same way as the instcombine pass do (see
InstructionCombining.cpp):

   // Lower dbg.declare intrinsics otherwise their value may be clobbered
   // by instcombiner.
   bool DbgDeclaresChanged = LowerDbgDeclare(F);

Do you agree? Ok to commit?

Did you forget to attach a patch? A patch with a test case showing the
problem you're describing would be great.

Also, patches should generally be sent to the llvm-commits list, not llvmdev.

I will create a patch with a testcase and send it to llvm-commits.

Regards
/ Karl-Johan Karlsson

#4

The jumpthreading algorithm might duplicate blocks, including
dbg.declare instrinsics. Avoid ending up with two dbg.declare
intrinsics for a single alloca, by using the same method as in
InstructionCombining. Lower the dbg.declare intrinsics into an
appropriate set of dbg.value instrinsics.

Regards
/ Karl-Johan Karlsson

jumpthreading.patch (5.27 KB)