[LLVMbugs] [Bug 17852] Assertion `!ValuesPerBlock[0].isUndefValue() && "Dead BB dominate this block"' failed.

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=17852

Andrew Trick <atrick at apple.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|REOPENED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #7 from Andrew Trick <atrick at apple.com> ---
Author: shuxin_yang
Date: Mon Nov 11 16:00:23 2013
New Revision: 194424

URL: http://llvm.org/viewvc/llvm-project?rev=194424&view=rev
Log:
 Fix PR17952.

The symptom is that an assertion is triggered. The assertion was added by
me to detect the situation when value is propagated from dead blocks.
(We can certainly get rid of assertion; it is safe to do so, because
propagating
value from dead block to alive join node is certainly ok.)

 The root cause of this bug is : edge-splitting is conducted on the fly,
the edge being split could be a dead edge, therefore the block that 
split the critial edge needs to be flagged "dead" as well.

 There are 3 ways to fix this bug:
 1) Get rid of the assertion as I mentioned eariler 
 2) When an dead edge is split, flag the inserted block "dead".
 3) proactively split the critical edges connecting dead and live blocks when
    new dead blocks are revealed.

 This fix go for 3) with additional 2 LOC.

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