[llvm-commits] [llvm] r142992 - in /llvm/trunk: lib/VMCore/Instructions.cpp test/Bitcode/shuffle.ll

[Mon Ping Wang]

The bit code reader tries to look up the constant based on an index.  If it is hasn't encountered the constant yet, it places a placeholder and fixes it up later.  This happens rarely and allows the reader to run in one pass.  Updating the verifier is a good idea.  I'll do that.

-- Mon Ping

On Oct 26, 2011, at 12:36 AM, Duncan Sands wrote:

> Hi,
> 
>> The bitcode reader can create an shuffle with a place holder mask which it will
>> fix up later. For this special case, allow such a mask to be considered valid.
>> <rdar://problem/8622574>
> 
> why does it create a placeholder - is it really needed?  I mean, I don't see any
> other special casing of UserOp in Instructions.cpp, so it seems that no other
> instructions do this - in which case what makes shufflevector different?  Also,
> if you do follow this route, maybe you can have the verifier check that the
> mask is really valid (no UserOp1).  This would catch bugs in which the
> placeholder leaked out of the bitcode reader somehow.
> 
> Ciao, Duncan.
> 
>> 
>> Added:
>>     llvm/trunk/test/Bitcode/shuffle.ll
>> Modified:
>>     llvm/trunk/lib/VMCore/Instructions.cpp
>> 
>> Modified: llvm/trunk/lib/VMCore/Instructions.cpp
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/VMCore/Instructions.cpp?rev=142992&r1=142991&r2=142992&view=diff
>> ==============================================================================
>> --- llvm/trunk/lib/VMCore/Instructions.cpp (original)
>> +++ llvm/trunk/lib/VMCore/Instructions.cpp Tue Oct 25 19:34:48 2011
>> @@ -1576,10 +1576,17 @@
>>          return false;
>>        }
>>      }
>> -  }
>> -  else if (!isa<UndefValue>(Mask)&&  !isa<ConstantAggregateZero>(Mask))
>> +  } else if (!isa<UndefValue>(Mask)&&  !isa<ConstantAggregateZero>(Mask)) {
>> +    // The bitcode reader can create a place holder for a forward reference
>> +    // used as the shuffle mask. When this occurs, the shuffle mask will
>> +    // fall into this case and fail. To avoid this error, do this bit of
>> +    // ugliness to allow such a mask pass.
>> +    if (const ConstantExpr* CE = dyn_cast<ConstantExpr>(Mask)) {
>> +      if (CE->getOpcode() == Instruction::UserOp1)
>> +        return true;
>> +    }
>>      return false;
>> -
>> +  }
>>    return true;
>>  }
>> 
>> 
>> Added: llvm/trunk/test/Bitcode/shuffle.ll
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Bitcode/shuffle.ll?rev=142992&view=auto
>> ==============================================================================
>> --- llvm/trunk/test/Bitcode/shuffle.ll (added)
>> +++ llvm/trunk/test/Bitcode/shuffle.ll Tue Oct 25 19:34:48 2011
>> @@ -0,0 +1,31 @@
>> +; RUN: llvm-as<  %s | llvm-dis
>> +
>> +;<rdar://problem/8622574>
>> +; tests the bitcodereader can handle the case where the reader will initially
>> +; create shuffle with a place holder mask.
>> +
>> +
>> +define<4 x float>  @test(<2 x double>  %d2)  {
>> +entry:
>> +  %call20.i = tail call<4 x float>  @cmp(<2 x double>  %d2,
>> +<2 x double>  bitcast (
>> +<4 x float>  shufflevector (
>> +<3 x float>  shufflevector (
>> +<4 x float>  shufflevector (
>> +<3 x float>  bitcast (
>> +                                                  i96 trunc (
>> +                                                    i128 bitcast (<2 x double>  bitcast (
>> +<4 x i32>  <i32 0, i32 0, i32 0, i32 undef>  to<2 x double>)
>> +                                                    to i128) to i96)
>> +                                                  to<3 x float>),
>> +<3 x float>  undef,
>> +<4 x i32>  <i32 0, i32 1, i32 2, i32 undef>),
>> +<4 x float>  undef,
>> +<3 x i32>  <i32 0, i32 1, i32 2>),
>> +<3 x float>  undef,
>> +<4 x i32>  <i32 0, i32 1, i32 2, i32 undef>)
>> +                                          to<2 x double>))
>> +  ret<4 x float>  %call20.i
>> +}
>> +
>> +declare<4 x float>  @cmp(<2 x double>,<2 x double>)
>> 
>> 
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