[LLVMdev] debug info for llvm::IntrinsicInst ???

[reed kotler]

Ok.

I'm basically just following the model of the other fast-isel ports.

On 01/30/2015 09:12 PM, David Blaikie wrote:
> (I'm assuming you're building LLVM with clang, in this case?)
>
> Looks like IntrinsicInst is one of those "lies" in LLVM that works via 
> type punning that's undefined behavior in C++, so it's code that 
> should be fixed anyway.
>
> In any case, the reason this produces the debugging experience you're 
> seeing is that LLVM (& GCC, for that matter) assumes that if your 
> class has virtual functions, such as IntrinsicInst, here - then to use 
> the type one must've emitted the vtable for the type somewhere (the 
> C++ standard requires this - if you odr use the type, all the virtual 
> functions must be defined somewhere in the program). The debug info 
> emission attempts to reduce the number of times the debug info for the 
> type is emitted by piggybacking on this fact - producing the type 
> definition only where the vtable is produced.
>
> As it turns out, with this class, the vtable is never emitted. This is 
> because the type has no key function (no non-inline virtual function) 
> and the ctor itself is never emitted, so the vtable is never needed... 
> and thus no debug info.
>
> The right way to fix this is to stop relying on undefined type punning 
> - though I don't know enough about the APIs here to say just how to 
> achieve that goal.
>
> On Fri, Jan 30, 2015 at 8:55 PM, reed kotler <rkotler at mips.com 
> <mailto:rkotler at mips.com>> wrote:
>
>     When trying to display and do anything with a variable of type
>     IntrinsicInst, gdb thinks that it's an incomplete
>     type and kind find any member functions or even display the class.
>
>
>
>
>     (gdb) list 1337
>     1332
>     1333      // Finish off the call including any return values.
>     1334      return finishCall(CLI, RetVT, NumBytes);
>     1335    }
>     1336
>     1337    bool MipsFastISel::fastLowerIntrinsicCall(const
>     IntrinsicInst *II) {
>     1338      switch (II->getIntrinsicID()) {
>     1339      default:
>     1340        return false;
>     1341      case Intrinsic::bswap: {
>     (gdb) print II
>     $10 = (const llvm::IntrinsicInst *) 0x61b8ec8
>     (gdb) print *II
>     $11 = <incomplete type>
>     (gdb) call II->getIntrinsicID()
>     Couldn't find method llvm::IntrinsicInst::getIntrinsicID
>     (gdb)
>
>
>     However, up the call tree:
>
>     (gdb) frame 3
>     #3  0x000000000368db6d in llvm::FastISel::selectOperator
>     (this=0x6235290,
>         I=0x61b8ec8, Opcode=49)
>         at
>     /home/rkotler/workspace/llvm/lib/CodeGen/SelectionDAG/FastISel.cpp:1535
>     1535        return selectCall(I);
>     (gdb) list 1535
>     1530
>     1531        // Dynamic-sized alloca is not handled yet.
>     1532        return false;
>     1533
>     1534      case Instruction::Call:
>     1535        return selectCall(I);
>     1536
>     1537      case Instruction::BitCast:
>     1538        return selectBitCast(I);
>     1539
>     (gdb) call I->dump()
>       %2 = call float @llvm.powi.f32(float %0, i32 %1)
>     (gdb)
>     (gdb) print *I
>     $12 = {<llvm::Value> = {
>         _vptr$Value = 0x60c67f0 <vtable for llvm::CallInst+16>, VTy =
>     0x61035c0,
>         UseList = 0x61d3310, NameAndIsUsedByMD = {Value = 0},
>     SubclassID = 68 'D',
>         HasValueHandle = 0 '\000', SubclassOptionalData = 0 '\000',
>         SubclassData = 0, NumOperands = 3, static MaximumAlignment =
>     536870912},
>       OperandList = 0x61b8e80}
>     (gdb)
>
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