Marking a builtin function as `noreturn'.

[Daniel Towner <daniel dot towner at picochip dot com>]

Hi all,

I maintain a port of gcc for an embedded processor which has a HALT 
instruction. This instruction stops the processor, and generates an 
appropriate interrupt to indicate to its parent system that it has 
stopped. The instruction is accessed by the programmer using a 
port-specific builtin, which can then be used, amongst other things, to 
implement the `assert' macro.

At the moment, whenever a HALT instruction is emitted, the compiler 
still seems to assume that execution will continue after the HALT 
instruction has executed (e.g., the compiler emits branches to the 
function epilogue, etc.). I would like the compiler to treat the builtin 
instruction as though it had the attribute `noreturn'. I have added this 
attribute to the builtin declaration in the TARGET_INIT_BUILTINS 
function, but it appears to make no difference. I may have got the code 
wrong, but assuming the code is correct, should gcc allow a builtin to 
be marked as a noreturn? Should a builtin marked in this way stop any 
code flow after the HALT? Is there another way to achieve the effect I 
am after?

Thanks,

dan.

--
============================================================================
Daniel Towner
picoChip Designs Ltd, Riverside Buildings, 108, Walcot Street, BATH, BA1 5BG
daniel.towner@picochip.com
+44 (0) 7786 702589