[LLVMdev] instruction CE_GEP

[Le Anh Quang]

Hi all,

 

I have a question with the ”getelemptr” instruction.

E.g.: I have some GEP instructions in my program.

Some look like:

 

 <INST_GEP op0=26 op1=64 op2=429/>

…

<INST_GEP op0=341 op1=64 op2=101 op3=499 op4=0/>

 

The first instruction above in assembly file:

%tmp60 = getelementptr [512 x i32]* @weights, i32 0, i32 %k.3.ph

Ok, we see it all:

Index of @weights in value list = 26

Index of “i32 0” in value list = 64

Index of “i32 %k.3.ph” in value list = 429

 

But in the second instructions:

%tmp67.1 = getelementptr [8 x [8 x i32]]* %inter, i32 0, i32 1, i32 %outc.0.reg2mem.0

As the first one, we see:

Index of %inter  in value list = 341

Index of “i32 0” in value list = 64

Index of “i32 1” in value list = 101

Index of “i32 %outc.0.reg2mem.0” in value list = 499

 

è What is the last one, “op4=0” ?

And the index of the second instruction in value list is less than 499.

 

Thanks for any advice.

Quang

[Chris Lattner]

The type of a value is only encoded for forward references.  Please see the source for the bitcode reader for more information.  Here's a snippet that is useful:

  /// getValueTypePair - Read a value/type pair out of the specified record from

  /// slot 'Slot'.  Increment Slot past the number of slots used in the record.

  /// Return true on failure.

  bool getValueTypePair(SmallVector<uint64_t, 64> &Record, unsigned &Slot,

                        unsigned InstNum, Value *&ResVal) {

    if (Slot == Record.size()) return true;

    unsigned ValNo = (unsigned)Record[Slot++];

    if (ValNo < InstNum) {

      // If this is not a forward reference, just return the value we already

      // have.

      ResVal = getFnValueByID(ValNo, 0);

      return ResVal == 0;

    } else if (Slot == Record.size()) {

      return true;

    }

    

    unsigned TypeNo = (unsigned)Record[Slot++];

    ResVal = getFnValueByID(ValNo, getTypeByID(TypeNo));

    return ResVal == 0;

  }

-Chris