[llvm] r304123 - Don't capture a temporary std::string in a StringRef.

[Craig Topper via llvm-commits]

Hmm the one I fixed earlier was a similar getValueAsString being captured
in to a StringRef. I unable to reproduce it with debug symbols enabled, but
valgrind was able to flag it as an invalid access. But valgrind wasn't
flagging the one you fixed. Does MSVC's implementation of std::string null
terminates the array before destructing?

~Craig

On Sun, May 28, 2017 at 7:38 PM, Zachary Turner <zturner at google.com> wrote:

> Also it wasn't actually "crashing", it was hitting the llvm_unreachable at
> the bottom of this function.
>
> On Sun, May 28, 2017 at 7:38 PM Zachary Turner <zturner at google.com> wrote:
>
>> Just let it crash under the debugger, and when I looked at Name it was
>> "\0em16".  But when I stepped into getValueAsString it looked like it was
>> indeed returning "Mem16", which should have been correct.  So there was
>> obviously some memory corruption, but since it happened in such a narrow
>> time frame (between the return statement and assigning the value to the
>> StringRef, there weren't really a lot of possibilities.  So when I checked
>> the function signature, sure enough it was returning a std::string.
>>
>> On Sun, May 28, 2017 at 7:33 PM Craig Topper <craig.topper at gmail.com>
>> wrote:
>>
>>> How did you narrow it down to that?
>>>
>>> ~Craig
>>>
>>> On Sun, May 28, 2017 at 7:20 PM, Zachary Turner via llvm-commits <
>>> llvm-commits at lists.llvm.org> wrote:
>>>
>>>> Author: zturner
>>>> Date: Sun May 28 21:20:12 2017
>>>> New Revision: 304123
>>>>
>>>> URL: http://llvm.org/viewvc/llvm-project?rev=304123&view=rev
>>>> Log:
>>>> Don't capture a temporary std::string in a StringRef.
>>>>
>>>> This fixes the breakages in llvm-tblgen.
>>>>
>>>> Modified:
>>>>     llvm/trunk/utils/TableGen/X86FoldTablesEmitter.cpp
>>>>
>>>> Modified: llvm/trunk/utils/TableGen/X86FoldTablesEmitter.cpp
>>>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/utils/
>>>> TableGen/X86FoldTablesEmitter.cpp?rev=304123&r1=304122&r2=
>>>> 304123&view=diff
>>>> ============================================================
>>>> ==================
>>>> --- llvm/trunk/utils/TableGen/X86FoldTablesEmitter.cpp (original)
>>>> +++ llvm/trunk/utils/TableGen/X86FoldTablesEmitter.cpp Sun May 28
>>>> 21:20:12 2017
>>>> @@ -285,7 +285,7 @@ getMemOperandSize(const Record *MemRec,
>>>>          (MemRec->getName() == "sdmem" || MemRec->getName() == "ssmem"))
>>>>        return 128;
>>>>
>>>> -    StringRef Name =
>>>> +    std::string Name =
>>>>          MemRec->getValueAsDef("ParserMatchClass")->
>>>> getValueAsString("Name");
>>>>      if (Name == "Mem8")
>>>>        return 8;
>>>>
>>>>
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>>>>
>>>
>>>
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