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a68e72a0c8
Summary: LAA can only emit run-time alias checks for pointers with affine AddRec SCEV expressions. However, non-AddRecExprs can be now be converted to affine AddRecExprs using SCEV predicates. This change tries to add the minimal set of SCEV predicates in order to enable run-time alias checking. Reviewers: anemet, mzolotukhin, mkuper, sanjoy, hfinkel Reviewed By: hfinkel Subscribers: mssimpso, Ayal, dorit, roman.shirokiy, mzolotukhin, llvm-commits Differential Revision: https://reviews.llvm.org/D17080 llvm-svn: 313012
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))
//===---------------------------------------------------------------------===//