[llvm-commits] [PATCH] treat calls to noreturn functions as side effecting

[Richard Osborne]

Currently at -O2 a call to a readonly noreturn function (e.g. a function 
consisting of while(1)) is replaced by unreachable, which seems somewhat 
nasty. The following sequence of transforms are responsible:

1) prune-eh adds unreachable after the call (since it has the noreturn 
attribute)
2) early-cse removes the call to the function (since it has the readonly 
attribute).

This patch makes Instruction::hasSideEffect() return true for functions 
marked with the no return attribute avoid this.
To be completely correct early-cse (and others) should be updated so 
that they only delete calls to functions that provably always return (or 
are marked as such) - see PR965. While this would be nice to fix it is 
also a much bigger slice of work.

Does this patch seem reasonable?

-- 
Richard Osborne | XMOS
http://www.xmos.com

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