llvm dev - Sep 2007 - [LLVMdev] Seeing a crash with ConstantFP::get

On Sep 5, 2007, at 5:08 PM, Chuck Rose III wrote:
> Hola Dale,
>
>
>
> I spent some time walking through what’s going on with a friend of  
> mine from VStudio.  Category is given 2 bits in the APFloat class  
> definition.  It’s sign extending the enum value for the comparisons  
> when it loads it out of the class, so the 2 becomes a -2 and the  
> comparison fails.  He sent me a piece of code which I might be able  
> to use to force the issue.  I’ll update when I try that out.
OK.  This possibility occurred to me, I checked the C++ standard, and  
the code is valid; this is explicitly required to work, and there's  
an example.
However VStudio is what it is.  I expect expanding the field to 3  
bits is good enough.  I don't think that will hurt
anything.
> Thanks,
>
> Chuck.
>
>
>
> From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev- 
> bounces at cs.uiuc.edu] On Behalf Of Chuck Rose III
> Sent: Wednesday, September 05, 2007 2:51 PM
> To: LLVM Developers Mailing List
> Subject: Re: [LLVMdev] Seeing a crash with ConstantFP::get
>
>
>
> It’s in debug.  I’m having a look at the assembler it’s producing  
> right now and it’s definitely a little odd for what should be a  
> simple assignment in zeroSignificand.
>
>
>
> From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev- 
> bounces at cs.uiuc.edu] On Behalf Of Dale Johannesen
> Sent: Wednesday, September 05, 2007 2:39 PM
> To: LLVM Developers Mailing List
> Subject: Re: [LLVMdev] Seeing a crash with ConstantFP::get
>
>
>
>
>
> On Sep 5, 2007, at 2:21 PM, Chuck Rose III wrote:
>
>
>
> Hola LLVMers,
>
>
>
> I’m getting a crash when using ConstantFP::get.
>
>
>
> I can repro it by adding one line to the Fibonacci example program:
>
>
>
> int main(int argc, char **argv) {
>
>   int n = argc > 1 ? atol(argv[1]) : 24;
>
>
>
>   // Create some module to put our function into it.
>
>   Module *M = new Module("test");
>
>
>
>   // We are about to create the "fib" function:
>
>   Function *FibF = CreateFibFunction(M);
>
>
>
> // add the following line
>
>   Constant* C = ConstantFP::get(Type::FloatTy,0.0);
>
>
>
>
>
> Can someone verify this?  This is on the PC side of my system which  
> I build with the VStudio files.  I don’t know if the Mac side sees  
> this as well, but I’ll try and verify.  Seems really odd to have  
> something this basic crash me.  It came up because the JITter will  
> call ConstantFP::get with the GenericValue arguments passed it, but  
> the above repro is a lot simpler and is independent of the JITter.
>
>
>
> My call stack looks like this:
>
>
>
>             in here it fails this:  assert(category == fcNormal ||  
> category == fcNaN);
>
>             Fibonacci.exe!llvm::APFloat::significandParts()  Line  
> 360 + 0x39 bytes    C++
>
>             Fibonacci.exe!llvm::APFloat::zeroSignificand()  Line  
> 387 + 0x15 bytes     C++
>
> I've been working in this area and probably introduced this, but I  
> don't see how:  zeroSignificand() sets 'category' to fcNormal  
> before calling significandParts, so I don't see how that assert  
> could be triggered.   The call stack looks normal for that source  
> line.  It doesn't appear on the Mac.   Could your compiler be  
> misoptimizing the code?
>
>>             Fibonacci.exe!llvm::APFloat::APFloat(const  
>> llvm::fltSemantics & ourSemantics={...}, unsigned __int64  
>> value=1)  Line 307       C++
>>
>>             Fibonacci.exe!`anonymous  
>> namespace'::DenseMapAPFloatKeyInfo::getEmptyKey()  Line 277 + 0x11
>> bytes         C++
>>
>>             Fibonacci.exe!llvm::DenseMap<`anonymous  
>> namespace'::DenseMapAPFloatKeyInfo::KeyTy,llvm::ConstantFP  
>> *,A0x5b1fa632::DenseMapAPFloatKeyInfo>::getEmptyKey()  Line 236 +  
>> 0x9 bytes          C++
>>
>>             Fibonacci.exe!llvm::DenseMap<`anonymous  
>> namespace'::DenseMapAPFloatKeyInfo::KeyTy,llvm::ConstantFP  
>> *,A0x5b1fa632::DenseMapAPFloatKeyInfo>::init(unsigned int  
>> InitBuckets=64)  Line 295 + 0x9 bytes         C++
>>
>>             Fibonacci.exe!llvm::DenseMap<`anonymous  
>> namespace'::DenseMapAPFloatKeyInfo::KeyTy,llvm::ConstantFP  
>> *,A0x5b1fa632::DenseMapAPFloatKeyInfo>::DenseMap<`anonymous  
>> namespace'::DenseMapAPFloatKeyInfo::KeyTy,llvm::ConstantFP  
>> *,A0x5b1fa632::DenseMapAPFloatKeyInfo>(unsigned int  
>> NumInitBuckets=64)  Line 68      C++
>>
>>             Fibonacci.exe! 
>> llvm::ManagedStatic<llvm::DenseMap<`anonymous  
>> namespace'::DenseMapAPFloatKeyInfo::KeyTy,llvm::ConstantFP  
>> *,A0x5b1fa632::DenseMapAPFloatKeyInfo> >::LazyInit()  Line 72 +  
>> 0x24 bytes     C++
>>
>>             Fibonacci.exe! 
>> llvm::ManagedStatic<llvm::DenseMap<`anonymous  
>> namespace'::DenseMapAPFloatKeyInfo::KeyTy,llvm::ConstantFP  
>> *,A0x5b1fa632::DenseMapAPFloatKeyInfo> >::operator*()  Line 55 
C++
>>
>>             Fibonacci.exe!llvm::ConstantFP::get(const llvm::Type *  
>> Ty=0x01b352d8, double V=0.00000000000000000)  Line 299 + 0xe  
>> bytes          C++
>>
>>             Fibonacci.exe!main(int argc=1, char * *  
>> argv=0x01b35060)  Line 99 + 0x13 bytes  C++
>>
>>             Fibonacci.exe!__tmainCRTStartup()  Line 586 + 0x19  
>> bytes         C
>>
>>             Fibonacci.exe!mainCRTStartup()  Line 403          C
>>
>>
>>
>> Thanks,
>>
>> Chuck.
>>
>> _______________________________________________
>>
>> LLVM Developers mailing list
>>
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>>
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>>
>
>
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Dale Johannesen wrote:-
> >I spent some time walking through what?s going on with a friend of  
> >mine from VStudio.  Category is given 2 bits in the APFloat class  
> >definition.  It?s sign extending the enum value for the comparisons  
> >when it loads it out of the class, so the 2 becomes a -2 and the  
> >comparison fails.  He sent me a piece of code which I might be able  
> >to use to force the issue.  I?ll update when I try that out.
> OK.  This possibility occurred to me, I checked the C++ standard, and  
> the code is valid; this is explicitly required to work, and there's  
> an example.
Thought this might be my bug for a moment.

4.5p3 right?  "If the bit-field has an enumerated type, it is
treated as any other value of that type for promotion purposes".
So the bitfield promotes like the enumeration constant itself and
the comparison should be good.  It would be pretty sad indeed if
assigning an enum of that type to the bitfield didn't then compare
equal to itself :)
> However VStudio is what it is.  I expect expanding the field to
> 3 bits is good enough.  I don't think that will hurt anything.
MSVC--.

Neil.

On Sep 6, 2007, at 6:01 AM, Neil Booth wrote:
> Dale Johannesen wrote:-
>
>>> I spent some time walking through what?s going on with a friend of
>>> mine from VStudio.  Category is given 2 bits in the APFloat class
>>> definition.  It?s sign extending the enum value for the comparisons
>>> when it loads it out of the class, so the 2 becomes a -2 and the
>>> comparison fails.  He sent me a piece of code which I might be able
>>> to use to force the issue.  I?ll update when I try that out.
>> OK.  This possibility occurred to me, I checked the C++ standard, and
>> the code is valid; this is explicitly required to work, and there's
>> an example.
>
> Thought this might be my bug for a moment.
>
> 4.5p3 right?  "If the bit-field has an enumerated type, it is
> treated as any other value of that type for promotion purposes".
> So the bitfield promotes like the enumeration constant itself and
> the comparison should be good.
You might argue with that one if you didn't feel like changing your
compiler, but 9 .6p4 is quite explicit:

... If the value of an enumerator is stored into a bitfield
of the same enumeration type and the number of bits in the bitfield
is large enough to hold all the values of that enumeration type, the
original enumerator value and the value of the bitfield
shall compare equal. [Example:
enum BOOL { f=0, t=1 };
struct A {
BOOL b:1;
};
A a;
void f() {
a.b = t;
if (a.b == t) // shall yield true
{ /* ... */ }
}
—end example]

Looks just like your code.
> It would be pretty sad indeed if
> assigning an enum of that type to the bitfield didn't then compare
> equal to itself :)
I agree.  So did the committee.
>> However VStudio is what it is.  I expect expanding the field to
>> 3 bits is good enough.  I don't think that will hurt anything.
>
> MSVC--.
>
> Neil.
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
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