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Re: [PATCH] Add new built-in: __builtin_unreachable()


Ian Lance Taylor wrote:
David Daney <ddaney@caviumnetworks.com> writes:

+@deftypefn {Built-in Function} void __builtin_unreachable (void)
+This function is used to indicate to the compiler that control flow
+will never reach the point of the @code{__builtin_unreachable}.  If
+control flow does reach @code{__builtin_unreachable}, program behavior
+is undefined.  The only valid use of this builtin is immediately
+following an @code{asm} statement that either never exits or transfers
+control elsewhere never returning.

I have wanted __builtin_unreachable for a while, but never got around to doing anything. But I only want it if it works in general, not just after an asm statement. I think it should mean "if control flow reaches this point, the program is undefined." Ideally there should be a command line option to control it, so that it is possible to compile __builtin_unreachable as expanding to abort, or something like that, when debugging.

That should be fairly simple. Just call expand_builtin_trap() instead if the command line flag is set.


If I can fix the ICE that Richi's testcase generates, I will roll this change in to the next version of the patch.

Thanks,
David Daney


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