[llvm-commits] [llvm] r130485 - in /llvm/trunk: lib/Transforms/InstCombine/InstCombineShifts.cpp test/Transforms/InstCombine/shift.ll
Devang Patel
dpatel at apple.com
Mon May 2 14:17:20 PDT 2011
On May 1, 2011, at 12:40 PM, Chris Lattner wrote:
> On Apr 30, 2011, at 3:22 AM, Benjamin Kramer wrote:
>
>>
>> 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.
>
> More generally, we don't want to sprinkle setDebugLoc calls into *every* instcombine xform.
One other alternative is to consistently use IRBuilder.
> We need a better solution.
I agree.
-
Devang
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