[llvm-commits] [llvm] r127834 - in /llvm/trunk: include/llvm/Transforms/Utils/Local.h lib/Transforms/InstCombine/InstructionCombining.cpp lib/Transforms/Utils/Local.cpp test/Transforms/InstCombine/debuginfo.ll

[Eli Friedman]

On Thu, Mar 17, 2011 at 3:41 PM, Devang Patel <dpatel at apple.com> wrote:
>
> On Mar 17, 2011, at 3:36 PM, Eli Friedman wrote:
>
>> On Thu, Mar 17, 2011 at 3:18 PM, Devang Patel <dpatel at apple.com> wrote:
>>> Author: dpatel
>>> Date: Thu Mar 17 17:18:16 2011
>>> New Revision: 127834
>>>
>>> URL: http://llvm.org/viewvc/llvm-project?rev=127834&view=rev
>>> Log:
>>> Try to not lose variable's debug info during instcombine.
>>> This is done by lowering dbg.declare intrinsic into dbg.value intrinsic.
>>> Radar 9143931.
>>
>> This looks like the wrong solution to a problem only caused by a few
>> very specific pieces of instcombine.  Adding an extra iteration over
>> every instruction in the function isn't cheap
>
> instcombine is already going to iterator over once. If there are compile time regressions because of this patch, I'll take a look asap.

Not sure there will be; worth watch for, though.

>> , and it looks like this
>> could do some serious damage to the debug info for cases other than
>> the given testcase.
>
> ?

Assuming I'm reading the change correctly, take an example like the following:
void foo(int* x) { *x = 10; }
int bar(int i) {
  int a;
  a = i;
  foo(&a);
  return a; // If you "print a" at this point, you'll get the value of
i, not 10.
}

-Eli