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e836f05d00
It is not sound to mark the increment operation as `nuw` or `nsw` based on a proof off of the add recurrence if the increment operation we emit happens to be a `sub` instruction. I could not come up with a test case for this -- the cases where SCEVExpander decides to emit a `sub` instruction is quite small, and I cannot think of a way I'd be able to get SCEV to prove that the increment does not overflow in those cases. Differential Revision: http://reviews.llvm.org/D7899 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@230673 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))
//===---------------------------------------------------------------------===//