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LLVM Essentials

You're reading from   LLVM Essentials Become familiar with the LLVM infrastructure and start using LLVM libraries to design a compiler

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Product type Paperback
Published in Dec 2015
Publisher
ISBN-13 9781785280801
Length 166 pages
Edition 1st Edition
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Authors (4):
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Suyog Sarda Suyog Sarda
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Suyog Sarda
Mayur Pandey Mayur Pandey
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Mayur Pandey
David Farago David Farago
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David Farago
John Criswell John Criswell
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John Criswell
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Toc

Emitting a global variable


Global variables have visibility of all the functions within a given module. LLVM provides the GlobalVariable class to create global variables and set its properties such as linkage type, alignment, and so on. The Module class has the method getOrInsertGlobal() to create a global variable. It takes two arguments—the first is the name of the variable and the second is the data type of the variable.

As global variables are part of a module, we create global variables after creating the module. Insert the following code just after creating the module in toy.cpp:

GlobalVariable *createGlob(IRBuilder<> &Builder, std::string Name) {
  ModuleOb->getOrInsertGlobal(Name, Builder.getInt32Ty());
  GlobalVariable *gVar = ModuleOb->getNamedGlobal(Name);
  gVar->setLinkage(GlobalValue::CommonLinkage);
  gVar->setAlignment(4);
  return gVar;
}

Linkage is what determines if multiple declarations of the same object refer to the same object, or to separate ones...

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