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49d728ad21
LazyCallGraph to support repeated, stable iterations, even in the face of graph updates. This is particularly important to allow the CGSCC pass manager to walk the RefSCCs (and thus everything else) in a module more than once. Lots of unittests and other tests were hard or impossible to write because repeated CGSCC pass managers which didn't invalidate the LazyCallGraph would conclude the module was empty after the first one. =[ Really, really bad. The interesting thing is that in many ways this simplifies the code. We can now re-use the same code for handling reference edge insertion updates of the RefSCC graph as we use for handling call edge insertion updates of the SCC graph. Outside of adapting to the shared logic for this (which isn't trivial, but is *much* simpler than the DFS it replaces!), the new code involves putting newly created RefSCCs when deleting a reference edge into the cached list in the correct way, and to re-formulate the iterator to be stable and effective even in the face of these kinds of updates. I've updated the unittests for the LazyCallGraph to re-iterate the postorder sequence and verify that this all works. We even check for using alternating iterators to trigger the lazy formation of RefSCCs after mutation has occured. It's worth noting that there are a reasonable number of likely simplifications we can make past this. It isn't clear that we need to keep the "LeafRefSCCs" around any more. But I've not removed that mostly because I want this to be a more isolated change. Differential Revision: https://reviews.llvm.org/D24219 llvm-svn: 281716
Analysis Opportunities:
//===---------------------------------------------------------------------===//
In test/Transforms/LoopStrengthReduce/quadradic-exit-value.ll, the
ScalarEvolution expression for %r is this:
{1,+,3,+,2}<loop>
Outside the loop, this could be evaluated simply as (%n * %n), however
ScalarEvolution currently evaluates it as
(-2 + (2 * (trunc i65 (((zext i64 (-2 + %n) to i65) * (zext i64 (-1 + %n) to i65)) /u 2) to i64)) + (3 * %n))
In addition to being much more complicated, it involves i65 arithmetic,
which is very inefficient when expanded into code.
//===---------------------------------------------------------------------===//
In formatValue in test/CodeGen/X86/lsr-delayed-fold.ll,
ScalarEvolution is forming this expression:
((trunc i64 (-1 * %arg5) to i32) + (trunc i64 %arg5 to i32) + (-1 * (trunc i64 undef to i32)))
This could be folded to
(-1 * (trunc i64 undef to i32))
//===---------------------------------------------------------------------===//