[LLVMdev] Eliminating gotos
resistor at mac.com
Mon Aug 11 19:14:55 PDT 2008
On Aug 11, 2008, at 2:02 PM, Benedict Gaster wrote:
> We would like to develop a code generator using LLVM for a target
> language that does not support conditional branches and in fact only
> supports structured control flow, eg. If and while.
What's the difference between an "if" and a conditional branch?
> As far as I can tell that the problem with doing this in LLVM today,
> is that it does not support these high-level constructs and instead
> all control flow is implemented as branches.
> It is “fairly” straightforward to restructure a program written with
> conditional/unconditional branches into to one that uses completely
> high-level control flow structures, the algorithm I have in mind is
> described in , the problem is how to best represent the resulting
> IL within the LLVM framework:
> Extend LLVM with news ops to support if/loop.
> Implement this with the insertion of intrinsics to represent high-
> level control-flow, introducing “false” dependencies if necessary to
> allow optimizations to be applied without changing the semantics.
> Implement some structure of to the side that represents this high-
> level flow.
One downside of this is that it means eliminating all instances of
irreducible control flow, which can lead to an exponential increase in
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