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c2a416a076
Summary: When splitting predecessors in BasicBlockUtils, we create a new block as an immediate predecessor of the original BB, then we connect a given set of predecessors to the new block. The API in this patch will be used to update MemoryPhis for this CFG change. If all predecessors are being moved, we move the MemoryPhi directly. Otherwise we create a new MemoryPhi in the NewBB and populate its incoming values, while deleting them from BB's Phi. [Split from D45299 for easier review] Reviewers: george.burgess.iv Subscribers: sanjoy, jlebar, Prazek, llvm-commits Differential Revision: https://reviews.llvm.org/D49156 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@337581 91177308-0d34-0410-b5e6-96231b3b80d8
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))
//===---------------------------------------------------------------------===//