The following line works successfully in LLVM:
%r1 = extractvalue [6 x i1] [i1 0, i1 1, i1 0, i1 1, i1 0, i1 0], 1
But the following line leads to an error in llc (notice the second index at the end of the line):
%r1 = extractvalue [6 x i1] [i1 0, i1 1, i1 0, i1 1, i1 0, i1 0], 1, 2
Error message: error: invalid indices for extractvalue.
Is it possible to get a slice of an array in LLVM?
Use extractvalue followed by one or more insertvalue instructions.
This will not look nice, but it'll result in the same native code output as a hypothetical nicer solution.
The syntax with multiple indices is there to support nested structs/arrays. If you want to extract an int from an array of array of ints, you need two indices.
Related
Say an array is declared as follows in LLVM IR:
...
#values = local_unnamed_addr constant [6 x i32] [i32 0, i32 1, i32 8, i32 27, i32 64, i32 125], align 16
...
This will show up when calling getGlobalList() on a Module object. How do I get the literal values {0, 1, 8, 27, 64, 125} from the GlobalVariable* representing values?
First, you get the [6 x i32] [i32 0, i32 1, i32 8, i32 27, i32 64, i32 125] by calling getInitializer(), then do cast<ConstantDataArray>() and finally use getElement* methods.
See http://llvm.org/doxygen/classllvm_1_1ConstantDataSequential.html
I am new to llvm programming, and I am trying to write cpp to generate llvm ir for a simple C code like this:
int a[10];
a[0] = 1;
I want to generate something like this to store 1 into a[0]
%3 = getelementptr inbounds [10 x i32], [10 x i32]* %2, i64 0, i64 0
store i32 1, i32* %3, align 16
And I tried CreateGEP: auto arrayPtr = builder.CreateInBoundsGEP(var, num); where var and
num are both of type llvm::Value*
but I only get
%1 = getelementptr inbounds [10 x i32], [10 x i32]* %0, i32 0
store i32 1, [10 x i32]* %1
I searched google for a long time and looked the llvm manual but still don't know what Cpp api to use and how to use it.
Really appreciate it if you can help!
Note that the 2nd argument to IRBuilder::CreateInBoundsGEP (1st overload) is actually ArrayRef<Value *>, which means it accepts an array of Value * values (including C-style array, std::vector<Value *> and std::array<Value *, LEN> and others).
To generate a GEP instruction with multiple (child) addresses, pass an array of Value * to the second argument:
Value *i32zero = ConstantInt::get(contexet, APInt(32, 0));
Value *indices[2] = {i32zero, i32zero};
builder.CreateInBoundsGEP(var, ArrayRef<Value *>(indices, 2));
Which will yield
%1 = getelementptr inbounds [10 x i32], [10 x i32]* %0, i32 0, i32 0
You can correctly identify that %1 is of type i32*, pointing to the first item in the array pointed to by %0.
LLVM documentation on GEP instruction: https://llvm.org/docs/GetElementPtr.html
I'm writing a simple code generating a simple list with 5 numbers whose first variable should be positive and I'm trying to understand why this code fails
test([H|T]) :- H > 0, length(T,4).
when I call with
length(X,5), test(X).
it shows me the following error:
ERROR: Arguments are not sufficiently instantiated
When I debug the code, the H variable in test isn't instantiated.
Anyone know why?
The issue here is that your rule for test([H|T]) doesn't describe in Prolog that H is a positive integer. It only tests if H > 0, which fails since H has not instantiation. Just attempting to compare an uninstantiated variable with a number (H > 0 in this case) doesn't cause Prolog to assume you intended H to be a number, and further, doesn't instantiate H.
Further, your rule for test/1 doesn't describe the rest of the list (T) other than to force that it be length 4. Since you're query establishes the rule that the length of the original list be 5, this stipulation is redundant.
You appear to be wanting to define test(L) such that it means L is an arbitrary list of positive integers. This is generally done using CLP(FD):
:- use_module(library(clpfd)).
test(X) :- X ins 1..10000.
This rule says that X is a list whose values are in the range 1 to 10000. The appropriate query to generate the lists of length 5 would then be:
?- length(X, 5), test(X), label(X).
X = [1, 1, 1, 1, 1] ;
X = [1, 1, 1, 1, 2] ;
X = [1, 1, 1, 1, 3] ;
X = [1, 1, 1, 1, 4] ;
X = [1, 1, 1, 1, 5] ;
...
If you want to restrict it further and say that elements need to be unique, you can use all_different/1:
test(X) :- X ins 1..10000, all_different(X).
?- length(X, 5), test(X), label(X).
X = [1, 2, 3, 4, 5] ;
X = [1, 2, 3, 4, 6] ;
X = [1, 2, 3, 4, 7] ;
X = [1, 2, 3, 4, 8] ;
X = [1, 2, 3, 4, 9] ;
X = [1, 2, 3, 4, 10] ;
...
I am trying to write an LLVM pass that counts instructions of vector type.
for instructions like :
%24 = or <2 x i64> %21, %23
%25 = bitcast <16 x i8> %12 to <8 x i16>
%26 = shl <8 x i16> %25, <i16 1, i16 1, i16 1, i16 1, i16 1, i16 1, i16 1, i16 1>
%27 = bitcast <8 x i16> %26 to <2 x i64>
I wrote this code:
for (auto &F : M) {
for (auto &B : F) {
for (auto &I : B) {
if (auto* VI = dyn_cast<InsertElementInst>(&I)) {
Value* op = VI->getOperand(0);
if (op->getType()->isVectorTy()){
++vcount;
}
}
But for some reason if (auto* VI = dyn_cast<InsertElementInst>(&I)) is never satisfied.
Any idea why?
Thanks in advance.
InsertElementInst is one specific instruction (that inserts an element into a vector) - and there is none in your list of instructiokns.
You probably want to dyn_cast to a regular use the Instruction in I as it is.
[I personally would use a one of the function or module pass classes as a base, so you only need to implement the inner loops of your code, but that's more of a "it's how you're supposed to do things", not something you HAVE to do to make it work].
In LLVM, the instruction is the same as it's result. so for an example
%25 = bitcast <16 x i8> %12 to <8 x i16>
when you cast Instruction I to value you get %25
Value* psVal = cast<Value>(&I);
and then you can check if it is of vector type or not by getType()->isVectorTy().
Also i suggest you look at inheritance diagram of llvm Value for more clarification
here http://llvm.org/docs/doxygen/html/classllvm_1_1Value.html
I am new to LLVM, and I am learning how to use LLVM for profiling. I need to pass an array to an external method, and insert a call instruction to the method in the code. I am currently using the following code, which on execution gives a segmentation fault.
std::vector<Value*> Args(1);
//Vector with array values
SmallVector<Constant*, 2> counts;
counts.push_back(ConstantInt::get(Type::getInt32Ty(BB->getContext()),32, false));
counts.push_back(ConstantInt::get(Type::getInt32Ty(BB->getContext()),12, false));
//Array with 2 integers
Args[0]= ConstantArray::get(llvm::ArrayType::get(llvm::Type::getInt32Ty(BI->getContext()),2), counts);
Here, the external function 'hook' is defined as M.getOrInsertFunction("hook", Type::getVoidTy(M.getContext()),
llvm::ArrayType::get(llvm::Type::getInt32Ty(BI->getContext()),2)
(Type*)0);
After reading a few source files, I've tried using GetElementPtrInst to pass the array
std::vector<Value*> ids(1);
ids.push_back(ConstantInt::get(Type::getInt32Ty(BB->getContext()),0));
Constant* array = ConstantArray::get(llvm::ArrayType::get(llvm::Type::getInt32Ty(BI->getContext()),2), counts);
Args[0] = ConstantExpr::getGetElementPtr(&(*array), ids, false);
but it fails with
7 opt 0x00000000006c59f5 bool llvm::isa<llvm::Constant, llvm::Value*>(llvm::Value* const&) + 24
8 opt 0x00000000006c5a0f llvm::cast_retty<llvm::Constant, llvm::Value*>::ret_type llvm::cast<llvm::Constant, llvm::Value*>(llvm::Value* const&) + 24
9 opt 0x0000000000b2b22f
10 opt 0x0000000000b2a4fe llvm::ConstantFoldGetElementPtr(llvm::Constant*, bool, llvm::ArrayRef<llvm::Value*>) + 55
11 opt 0x0000000000b33df2 llvm::ConstantExpr::getGetElementPtr(llvm::Constant*, llvm::ArrayRef<llvm::Value*>, bool) + 82
Also, in this case, 'hook' is defined as M.getOrInsertFunction("hook", Type::getVoidTy(M.getContext()),
PointerType::get(Type::getInt32PtrTy(M.getContext()),0), //when using GEP
(Type*)0);
Could someone kindly keep me a few pointers on passing arrays to an external function (say with the signature void hook(int abc[]) ). I am probably wrong all the way through, and would really appreciate some help.
A good place to start with "how do I do this c-like thing in LLVM IR" questions is to first write what you want to do in C, then compile it to LLVM IR via Clang and take a look at the result.
In your particular instance, the file:
void f(int a[2]);
void g() {
int x[2];
x[0] = 1;
x[1] = 3;
f(x);
}
Will compile to:
define void #g() nounwind {
%x = alloca [2 x i32], align 4
%1 = getelementptr inbounds [2 x i32]* %x, i32 0, i32 0
store i32 1, i32* %1, align 4
%2 = getelementptr inbounds [2 x i32]* %x, i32 0, i32 1
store i32 3, i32* %2, align 4
%3 = getelementptr inbounds [2 x i32]* %x, i32 0, i32 0
call void #f(i32* %3)
ret void
}
declare void #f(i32*)
So we can see the clang compiled g to receive i32*, not an array. That means you need a way to get an address to the first element of the array from the array itself, and a getelementptr instruction is a straightforward way of doing that.
Notice, however, that you want to generate a GEP (getelementptr instruction), for example via GetElementPtrInst::create. A gep constant expression, which is what you're trying to generate here, is something else, and will only work on compile-time constants.
You should use Clang to compile it. Then, check the boundaries of the array and if all the elements are defined.