[llvm-commits] patch: target option to disable tail calls

[Nick Lewycky]

The attached patch adds a new "-no-tail-calls" flag to llc, and implements
it in the x86 backend only. The intent is to support gcc's
-fno-optimize-sibling-calls in clang, which as far as I can tell just
disables tail calls period. The goal is to help ASAN produce correct stack
traces, which requires disabling all tail calls.

As an aside, there is a good reason to do this in the backend and not at
the IR-level. The "tail" marker is used to indicate things that are useful
to the optimizers themselves; for example alias analysis interprets the
presence of a tail marker as proof that the callee can't access any
alloca's in the caller, whether the pointer has been captured or not.

Please review!

Nick
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