As far as I know, when two pointers (or references) do not type alias each other, it is legal to for the compiler to make the assumption that they address different locations and to make certain optimizations thereof, e.g., reordering instructions. Therefore, having pointers to different types to have the same value may be problematic. However, I think this issue only applies when the two pointers are passed to functions. Within the function body where the two pointers are created, the compiler should be able to make sure the relationship between them as to whether they address the same location. Am I right?
As far as I know, when two pointers (or references) do not type alias each other, it is legal to for the compiler to make the assumption that they address different locations and to make certain optimizations thereof, e.g., reordering instructions.
Correct. GCC, for example, does perform optimizations of this form which can be disabled by passing the flag -fno-strict-aliasing.
However, I think this issue only applies when the two pointers are passed to functions. Within the function body where the two pointers are created, the compiler should be able to make sure the relationship between them as to whether they address the same location. Am I right?
The standard doesn't distinguish between where those pointers came from. If your operation has undefined behavior, the program has undefined behavior, period. The compiler is in no way obliged to analyze the operands at compile time, but he may give you a warning.