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llvmllvm-irllvm-c++-api

LLVM IR for addition and subtraction

I use "builder->CreateSub" and "builder->CreateAdd" to generate LLVM-IR for subtraction and addition.

        left = this->builder->CreateAlloca(llvm::Type::getInt32Ty(*this->llvm_context), nullptr, std::string("a1"));
        right = this->builder->CreateAlloca(llvm::Type::getInt32Ty(*this->llvm_context), nullptr, std::string("b2"));
        builder->CreateSub(left, right, "sub");
        builder->CreateAdd(left, right, "add");

However, the generated IR (shown below) cannot be compiled/interpreted by LLVM (lli)

 %a1 = alloca i32, align 4
 store i32 100, ptr %a1, align 4
 %b2 = alloca i32, align 4
 store i32 10, ptr %b2, align 4
 %add = add ptr %a1, %b2
 %sub = sub ptr %c3, i32 2
 %sub1 = sub ptr %add, %sub

Which gives error (on ptr):

 lli: lli: test.ll:14:14: error: invalid operand type for instruction
 %add = add ptr %a1, %b2
Solution

  • As pointed out by Nick Lewycky, we need load instruction to read memory from stack where alloca vars are stored. I added CreateLoad for left and right variables above.

    builder->CreateLoad(llvm::Type::getInt32Ty(*this->llvm_context), alloca);