-.. _gep:
-
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The Often Misunderstood GEP Instruction
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When people are first confronted with the GEP instruction, they tend to relate
it to known concepts from other programming paradigms, most notably C array
indexing and field selection. GEP closely resembles C array indexing and field
-selection, however it's is a little different and this leads to the following
+selection, however it is a little different and this leads to the following
questions.
What is the first index of the GEP instruction?
...
munge(Array);
-In this "C" example, the front end compiler (llvm-gcc) will generate three GEP
+In this "C" example, the front end compiler (Clang) will generate three GEP
instructions for the three indices through "P" in the assignment statement. The
function argument ``P`` will be the first operand of each of these GEP
instructions. The second operand indexes through that pointer. The third
structure containing a pointer to an array of 40 ints. The GEP instruction seems
to be accessing the 18th integer of the structure's array of ints. However, this
is actually an illegal GEP instruction. It won't compile. The reason is that the
-pointer in the structure <i>must</i> be dereferenced in order to index into the
+pointer in the structure *must* be dereferenced in order to index into the
array of 40 ints. Since the GEP instruction never accesses memory, it is
illegal.
Can I compute the distance between two objects, and add that value to one address to compute the other address?
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-As with arithmetic on null, You can use GEP to compute an address that way, but
+As with arithmetic on null, you can use GEP to compute an address that way, but
you can't use that pointer to actually access the object if you do, unless the
object is managed outside of LLVM.