[llvm-commits] [llvm] r130485 - in /llvm/trunk: lib/Transforms/InstCombine/InstCombineShifts.cpp test/Transforms/InstCombine/shift.ll

[Benjamin Kramer]

On 30.04.2011, at 00:00, Devang Patel wrote:

> 
> On Apr 29, 2011, at 2:50 PM, Benjamin Kramer wrote:
>> 
>> Are you sure this specific transformation destroys the DebugLoc? When InstCombine simply replaces one
>> instruction with another it preserves debug information (InstructionCombining.cpp:1592).
> 
> I added line 1592 however I am not sure that this particular transformation is covered by 1592 in all cases. I have seen "shl" without DebugLoc generated by instcombine before your patch landed in svn. If you're interested I can send you more info.

There is a way this transform can lose a DebugLoc

x = C1 <<  A # with DebugLoc
y = x  << C2 # without DebugLoc

InstCombine will then replace 'y' with a new instruction (but there's no DebugLoc to attach to it) and 'x' is DCE'd.
I think the only feasible way to improve here is to find out why 'y' has no debug info attached to it.

If you have a test case where InstCombine introduces SHLs without DebugLocs, I'd be interested in seeing it.