armcc or armclang versus gcc

I am trying to see if there is an advantage using the armcc/armclang compilers over the gcc compiler for ARM that is supplied by Linaro. Looking at the documentation for armcc and armclang I do not notice anything spectacular, so perhaps the community that uses these tools can better address the reason why one would want to pay for access to the arm-developed compilers?

Specifically, I am interested to know if the warnings/errors when compiling code that violates the architecture best practices (such as not using 32bit local variables in functions etc...) are better for the paid-for compilers.

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