[Patch] GVN fold conditional-branch on-the-fly

[Shuxin Yang]

On 9/10/13 7:56 AM, Nadav Rotem wrote:
> Hi Daniel,
>
> I reviewed the patch again and I realized that I was too optimistic. Yes, tryGetDomFrontier is very context specific and too complicated. I don’t understand why we need 4 of the 5 parameters.


> I think that shuxin should implement a simple generic function for finding Single-Entry-Single-Exit and use it. The code for finding SESE can be used elsewhere.
SESE for C, SEME for C++.
Why SEME? because exception handling.
Among all the exits of SEME, only one is normal exit, the rest is 
goto-landing-pad. That also why need to multiple parameter
in tryGetDomFrontier(), because we need to differentiate the the 
normal-exit and landing-pad show up in DF.

As you can see most of added code is to detect SESE/SEME, few is really 
about GVN.
It is not true to say it significantly complicate the existing code.



> The function eraseSubtree in Dominators.h should be rewritten and simplified.  The code for landing pads should be simplified or at least explained better. The function tryFoldCondBranch should be cleaned up.

> deleteDeadBlocks should be a static utility class, and simplified (DT should be an optional parameter to allow DT cleanup, etc).
Nope. Such dead block are quite special in that maintaining DT is quite 
simply,