On Nov 8, 2007, at 2:20 PM, Owen Anderson wrote:
> Author: resistor
> Date: Thu Nov 8 16:20:23 2007
> New Revision: 43910
>
> URL: http://llvm.org/viewvc/llvm-project?rev=43910&view=rev
> Log:
> Make BreakCriticalMachineEdges available as a pass that can be
> depended on.
Hey Owen,
Here's a really important case that is non-obvious:
consider:
switch ...
[1, BB1]
[2, BB1]
[3, BB1]
...
BB1:
X = phi [switchblock, x] [switchblock, x] [switchblock, x]
[otherblock, y]
All three edges between switchblock and BB1 are critical, yet it is
critially (haha) important that they be split as:
switch ...
[1, NewBB]
[2, NewBB]
[3, NewBB]
...
NewBB:
br BB1
BB1:
X = phi [BB1, x] [otherblock, y]
Note that in this case, the edges are still critical after the
xform... fun huh? :)
Also, I second Evan's concern about this being a pass. It seems like
it should be a function that passes can call when they need to. For
StrongPHI elim for example, it only really needs to split critical
edges to blocks that have phi's in them, right?
-Chris
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