[LLVMdev] Helping the optimizer along (__assume)

[Duncan Sands]

> Can't you implement __builtin_assume(cond) to codegen to something like:
> 
> 	%cond = i1 ...
> 	br i1 %cond, label %always, label %never
> never:
> 	unreachable
> always:

The code generators will remove the branch to %never.
I already tried this :)  What would work is to define
an llvm.abort intrinsic, and do:

 	%cond = i1 ...
 	br i1 %cond, label %always, label %never
 never:
    call void @llvm.abort()
 	unreachable

At codegen time @llvm.abort() can be lowered to
nothing at all.  I'm not saying that this is my
favorite solution, but it is simple.

Ciao,

Duncan.