[LLVMdev] How to get the string value?
Welson Sun
Duncan Sands
> Hi, if I have some LLVM code like this:
>
> @.str = private unnamed_addr constant [7 x i8] c"in_arr\00", align 1
> @.str1 = private unnamed_addr constant [8 x i8] c"in_arr2\00", align 1
> @.str2 = private unnamed_addr constant [8 x i8] c"out_arr\00", align 1
> ...
> ...
>
> call void (...)* @_Z16fooz(i8* *getelementptr inbounds ([7 x i8]* @.str, i64
> 0, i64 0)*, i32 0, i32 1024)
> ...
>
> I would like to get the string value of the bold argument, but how? I know it's
> a llvm::Value pointer, but it is not a llvm::GetElementPtrInst?
it is a ConstantExpr getelementptr. Whenever you see something that looks like
an instruction but is printed inline inside another instruction then that means
it is actually a constant, a ConstantExpr.
Ciao, Duncan.
>
>
> Thanks,
>
>
>
>
>
>
>
>
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Welson Sun
Welson Sun
| DECLARE_TRANSPARENT_OPERAND_ACCESSORS (Constant) | |
|
Transparently provide more efficient getOperand methods. | |
| bool | isCast () const |
|
Return true if this is a convert constant expression. | |
| bool | isCompare () const |
|
Return true if this is a compare constant expression. | |
| bool | hasIndices () const |
|
Return true if this is an insertvalue or extractvalue expression, and the getIndices() method may be used. | |
| bool | isGEPWithNoNotionalOverIndexing () const |
|
Return true if this is a getelementptr expression and all the index operands are compile-time known integers within the corresponding notional static array extents. Note that this is not equivalant to, a subset of, or a superset of the "inbounds" property. | |
| unsigned | getOpcode () const |
|
getOpcode - Return the opcode at the root of this constant expression |
|
| unsigned | getPredicate () const |
| ArrayRef<unsigned > | getIndices () const |
| const char * | getOpcodeName () const |
|
getOpcodeName - Return a string representation for an opcode. | |
| Constant * | getWithOperandReplaced (unsigned OpNo, Constant *Op) const |
| Constant * | getWithOperands (ArrayRef< Constant * > Ops) const |
| Constant * | getWithOperands (ArrayRef< Constant * > Ops, Type *Ty) const |
| virtual void | destroyConstant () |
| virtual void | replaceUsesOfWithOnConstant (Value *From, Value *To, Use *U) |
Only isGEPWithNoNotionalOverIndexing () returns true. But how are you supposed to use others to get the constant value?
Duncan Sands
> Yes, it is a ConstantExpr! Thank you!
>
> Now trying to find a clue in ConstantExpr's functions to get that string :-)
you can get the pointer operand by doing: getOperand(0)
The i'th index is getOperand(i+1).
Ciao, Duncan.
> > LLV...@cs.uiuc.edu <mailto:LLV...@cs.uiuc.edu> http://llvm.cs.uiuc.edu
> > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
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> --
> Welson
>
> Phone: (408) 418-8385
> Email: welso...@gmail.com <mailto:welso...@gmail.com>
Welson Sun
Duncan Sands
> Thanks! I figured out this piece of code finally:
>
> Value *gep = call->getArgOperand(0);
> if ( ConstantExpr *pCE = dyn_cast<ConstantExpr>(gep) ) {
> Value *firstop = pCE->getOperand(0);
> if (GlobalVariable *GV = dyn_cast<GlobalVariable>(firstop)){
> Constant *v = GV->getInitializer();
> if (ConstantArray *CA = dyn_cast<ConstantArray>(v)) {
> StringRef portName(CA->getAsString());
you can use stripPointerCasts to get rid of the GEP and similar pointer casts.
Ciao, Duncan.
>
> That's some learning experience :-)
>
> Regards,
> Welson
>
>
>
> On Sat, Jan 28, 2012 at 6:41 AM, Duncan Sands <bald...@free.fr
> <mailto:bald...@free.fr>> wrote:
>
> Hi Welson,
>
>
> Yes, it is a ConstantExpr! Thank you!
>
> Now trying to find a clue in ConstantExpr's functions to get that string :-)
>
>
> you can get the pointer operand by doing: getOperand(0)
> The i'th index is getOperand(i+1).
>
> Ciao, Duncan.
>
>
> Regards,
> Welson
>
> On Thu, Jan 26, 2012 at 9:04 PM, Duncan Sands <bald...@free.fr
> <mailto:bald...@free.fr>
> <mailto:LLV...@cs.uiuc.edu <mailto:LLV...@cs.uiuc.edu>>
> http://llvm.cs.uiuc.edu
>
> > http://lists.cs.uiuc.edu/ mailman/listinfo/llvmdev
> <http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev>
>
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>
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> <mailto:welso...@gmail.com <mailto:welso...@gmail.com>>
>
>
>
>
>
>
> --
> Welson
>
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