[LLVMdev] [cfe-dev] A problem with names that can not be demangled.

Fri Apr 17 11:42:44 PDT 2015

So looks like just adding a "." wold work. My preference would be to
do it for all Values and update the tests.

Also, the code currently looks like

-------------------------
 unsigned BaseSize = UniqueName.size();
  while (1) {
    // Trim any suffix off and append the next number.
    UniqueName.resize(BaseSize);
    raw_svector_ostream(UniqueName) << ++LastUnique;
-------------------------

Which means that currently if a name passes here multiple times we get

foo -> foo1 -> foo12

With the '.' we could change BaseSize to get

foo -> foo.1 -> foo.2

Cheers,
Rafael

On 16 April 2015 at 16:46, Cary Coutant <ccoutant at gmail.com> wrote:
> GCC has a generalized mangling syntax for cloned functions. See GCC PR 40831:
>
>    https://gcc.gnu.org/bugzilla/show_bug.cgi?id=40831
>
> and the discussion thread here:
>
>    https://gcc.gnu.org/ml/gcc-patches/2011-09/msg01375.html
>
> -cary
>
>
>
> On Tue, Apr 14, 2015 at 12:44 PM, David Blaikie <dblaikie at gmail.com> wrote:
>> Adding llvm-dev as that might be a more suitable audience for this
>> discussion.
>>
>> (& I know Lang's been playing around with the same problem in the Orc JIT,
>> so adding him too)
>>
>> Is there any basis/reason to believe that the .X suffix is a better, more
>> principled one than straight X? Is that documented somewhere as a thing the
>> demangling tools will ignore?
>>
>> On Tue, Apr 14, 2015 at 12:06 PM, Srivastava, Sunil
>> <sunil_srivastava at playstation.sony.com> wrote:
>>>
>>> Hi,
>>>
>>>
>>>
>>> We are running into a problem created by renaming of static symbols by
>>> llvm-link.  It first
>>>
>>> showed up using LTO, but we can illustrate this by using llvm-link as
>>> well.
>>>
>>>
>>>
>>> Say we have two files with the same named static symbol Bye
>>>
>>>
>>>
>>> --------------- t1.cpp ---------
>>>
>>> static void Bye(int* ba1) { ba1[0] /= ba1[2] - 2; }
>>>
>>> void main_a( int* inB) { void (*func)(int*) = Bye; func(inB); }
>>>
>>> --------------- t2.cpp ---------
>>>
>>> static void Bye(int* ba1) { ba1[0] *= ba1[2] + 2; }
>>>
>>> void main_b( int* inB) { void (*func)(int*) = Bye; func(inB+1); }
>>>
>>>
>>>
>>> --------- cmd sequence -------
>>>
>>> $ clang++ -c -emit-llvm t1.cpp -o t1.bc
>>>
>>> $ clang++ -c -emit-llvm t1.cpp -o t2.bc
>>>
>>> $ llvm-link t1.bc t2.bc -o t23.bc
>>>
>>> $ clang -c t23.bc
>>>
>>> $ nm t23.o
>>>
>>>
>>>
>>> t1.o and t2.o have the same named function “_ZL3ByePi”. In order to
>>> distinguish them,
>>>
>>> one gets a ‘1’ appended to it, making it  “_ZL3ByePi1”.
>>>
>>>
>>>
>>> While the code is all correct, the problem is that this modified name
>>> cannot be demangled.
>>>
>>>
>>>
>>> That is what I am trying to fix.
>>>
>>>
>>>
>>> In similar situations gcc appends a ‘.’ before appending the
>>> discriminating number, making “_ZL3ByePi.1”
>>>
>>>
>>>
>>> The following change in lib/IR/ValueSymbolTable.cpp seems to fix this
>>> problem.
>>>
>>>
>>>
>>> ------------ start diff -------------------
>>>
>>> @@ -54,5 +54,5 @@ void ValueSymbolTable::reinsertValue(Value* V) {
>>>
>>>      // Trim any suffix off and append the next number.
>>>
>>>      UniqueName.resize(BaseSize);
>>>
>>> -    raw_svector_ostream(UniqueName) << ++LastUnique;
>>>
>>> +    raw_svector_ostream(UniqueName) <<  "."  << ++LastUnique;
>>>
>>>
>>>
>>>      // Try insert the vmap entry with this suffix.
>>>
>>> -------------- end diff ---------------------
>>>
>>>
>>>
>>> However it causes 60 test failures. These are tests where some names that
>>> are expecting
>>>
>>> to get a plain numeric suffix now have a ‘.’ before it. These are all
>>> local symbols, so I think
>>>
>>> the generated code will always be correct, but the tests as written do not
>>> pass. For
>>>
>>> example, take test/CodeGen/ARM/global-merge-addrspace.ll
>>>
>>>
>>>
>>> ; RUN: llc < %s -mtriple=thumb-apple-darwin -O3 | FileCheck %s
>>>
>>> ; Test the GlobalMerge pass. Check that the pass does not crash when using
>>>
>>> ; multiple address spaces.
>>>
>>> ; CHECK: _MergedGlobals:
>>>
>>> @g1 = internal addrspace(1) global i32 1
>>>
>>> @g2 = internal addrspace(1) global i32 2
>>>
>>> ; CHECK: _MergedGlobals1:
>>>
>>> @g3 = internal addrspace(2) global i32 3
>>>
>>> @g4 = internal addrspace(2) global i32 4
>>>
>>>
>>>
>>> With my change, the symbol is named MergedGlobals.1, hence it fails this
>>> test.
>>>
>>>
>>>
>>> I could change these 60 tests to match the new behavior. That will fix
>>> these 60 failures.
>>>
>>> However, I do have a concern that there may be other places in llvm that
>>> expect the
>>>
>>> names to be pure identifiers. Adding a ‘.’ may cause them to fail. No such
>>> failure has been
>>>
>>> seen in running the whole clang test, but the concern is still there.
>>>
>>>
>>>
>>> I should note that even local symbols are treated similarly, so for
>>> example, a parameter
>>>
>>> named ‘str’ becomes ‘str.1’ with my change, instead of ‘str1’ currently
>>> (an actual
>>>
>>> example from a test).
>>>
>>>
>>>
>>> Alternatively, I could try to limit my change to just mangled names.
>>>
>>>
>>>
>>> Any suggestion about how this should be fixed ?
>>>
>>>
>>>
>>> There is another similar change about 40 lines below in
>>> ValueSymbolTable::createValueName().
>>>
>>> That is not needed to fix this particular problem, but looks similar, so
>>> perhaps should be treated
>>>
>>> similarly for consistency. It causes 66 more failures of the same nature
>>> though.
>>>
>>>
>>>
>>> Thanks
>>>
>>>
>>>
>>> Sunil Srivastava
>>>
>>> Sony Computer Entertainment
>>>
>>>
>>>
>>>
>>> _______________________________________________
>>> cfe-dev mailing list
>>> cfe-dev at cs.uiuc.edu
>>> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev
>>>
>>
>>
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