[PATCH] Exit ScalarEvolution::getMulExpr Early when Choose Overflows

[Thomas Jablin]

I have made the changes you suggested. The code is functionally equivalent to the original version, but the design of the original version is a bit unclear to me. Basically, the code is trying to combine many AddRecs into a single expression. The run-time is "only" N^2 in the size of Ops, because the second and third loop levels share indexes. I think the underlying issue is the expensive recursive calls to getMulExpr in the inner-most loop.

http://reviews.llvm.org/D5113

Files:
  lib/Analysis/ScalarEvolution.cpp
  test/Analysis/ScalarEvolution/choose-overflow-fast.ll
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