[LLVMdev] noob IR builder question

[mats petersson]

Maybe what you wanted was

   Value* c3 = builder.CreateFAdd(...);
   builder.CreateStore(a, c3);

?

On 10 March 2015 at 22:33, Hal Finkel <hfinkel at anl.gov> wrote:
> ----- Original Message -----
>> From: "Alan Nilsson" <alan.n at mac.com>
>> To: "LLVM Developers Mailing List" <llvmdev at cs.uiuc.edu>
>> Sent: Tuesday, March 10, 2015 5:15:23 PM
>> Subject: [LLVMdev] noob IR builder question
>>
>>
>> I am trying to get a handle on IR builder, at least some basics. I
>> ran through a tutorial here: Create a working compiler with the LLVM
>> framework, Part 1 , and it worked well enough. I have some simple
>> code that creates a hello world IR. I am trying to now bring in some
>> concepts from the Kaleidoscope tutorial, namely adding expressions
>> the the IR that is dumped out.
>>
>>
>> I’ve added the following snippets:
>>
>>
>> Value *c1 = ConstantFP::get(context, APFloat(1.0));
>> Value *c2 = ConstantFP::get(context, APFloat(3.0));
>> builder.CreateFAdd(c1, c2, "addtmp”);
>
> The IRBuilder has a builtin constant folder, and since you're not actually doing anything with the value returned, the constant that is created just goes away.
>
>  -Hal
>
>>
>>
>> expecting to see an add instruction in the dump, but nothing is
>> added. This seems to be pretty strait from the kaleidoscope examples
>> but I am missing something here I am sure. Here is the full program:
>>
>>
>>
>> 1 using namespace llvm;
>> 2
>> 3 llvm::Module *module;
>> 4 llvm::IRBuilder<> builder(getGlobalContext());
>> 5
>> 6 int main(int argc, const char * argv[]) {
>> 7 llvm::LLVMContext & context = llvm::getGlobalContext();
>> 8 module = new llvm::Module("calc", context);
>> 9
>> 10
>> 11 llvm::FunctionType *funcType =
>> llvm::FunctionType::get(builder.getVoidTy(), false);
>> 12 llvm::Function *mainFunc =
>> 13 llvm::Function::Create(funcType, llvm::Function::ExternalLinkage,
>> "main", module);
>> 14 llvm::BasicBlock *entry = llvm::BasicBlock::Create(context,
>> "entrypoint", mainFunc);
>> 15 builder.SetInsertPoint(entry);
>> 16
>> 17 llvm::Value *helloWorld = builder.CreateGlobalStringPtr("hello
>> world!\n");
>> 18
>> 19 std::vector<llvm::Type *> putsArgs;
>> 20 putsArgs.push_back(builder.getInt8Ty()->getPointerTo());
>> 21 llvm::ArrayRef<llvm::Type*> argsRef(putsArgs);
>> 22
>> 23 llvm::FunctionType *putsType =
>> 24 llvm::FunctionType::get(builder.getInt32Ty(), argsRef, false);
>> 25 llvm::Constant *putsFunc = module->getOrInsertFunction("puts",
>> putsType);
>> 26
>> 27 Value *a;
>> 28 builder.CreateAlloca(builder.getDoubleTy(), a, "a");
>> 29
>> 30 Value *c1 = ConstantFP::get(context, APFloat(1.0));
>> 31 Value *c2 = ConstantFP::get(context, APFloat(3.0));
>> 32 builder.CreateFAdd(c1, c2, "addtmp");
>> 33
>> 34 builder.CreateCall(putsFunc, helloWorld);
>> 35 builder.CreateRetVoid();
>> 36 module->dump();
>> 37 return 0;
>> 38 }
>>
>>
>> Produces:
>>
>>
>> ; ModuleID = 'calc'
>>
>> @0 = private unnamed_addr constant [14 x i8] c"hello world!\0A\00"
>>
>> define void @main() {
>> entrypoint:
>> %a = alloca double
>> %0 = call i32 @puts(i8* getelementptr inbounds ([14 x i8]* @0, i32 0,
>> i32 0))
>> ret void
>> }
>>
>> declare i32 @puts(i8*)
>>
>>
>> Lines 27-32 are the code I have added beyond the demo at the
>> mentioned website. As shown, the alloca shows up but no fadd
>> instruction. I would appreciate if someone could help me understand
>> this and point out what I am missing. Open to reading if someone can
>> point me to more documentation as well.
>>
>>
>> (llvm 3.5 downloaded from llvm.org on OSX)
>>
>>
>> thanks
>> alan
>> _______________________________________________
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>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>
>
> --
> Hal Finkel
> Assistant Computational Scientist
> Leadership Computing Facility
> Argonne National Laboratory
>
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