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|Home > Compiler Coding Practices > Unaligned Load Register (LDR) instructions generated by the compiler|
In some circumstances, where it is legal to do so, the compiler might intentionally generate unaligned
In particular, the compiler can do this to load halfwords from memory, even where the architecture supports dedicated halfword load instructions.
For example, to access an unaligned
short within a
__packed structure, the compiler might load the required halfword into
the top half of a register and then shift it down to the bottom half. This operation
requires only one memory access, whereas performing the same operation using
LDRB instructions requires two memory accesses, plus instructions to
merge the two bytes.