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51df7978a6
This patch adds a new singlecrfromundef lattice value, indicating a single element constant range which was merge with undef at some point. Merging it with another constant range results in overdefined, as we won't be able to replace all users with a single value. This patch uses a ConstantRange instead of a Constant*, because regular integer constants are represented as single element constant ranges as well and this allows the existing code working without additional changes. Reviewers: efriedma, nikic, reames, davide Reviewed By: efriedma Differential Revision: https://reviews.llvm.org/D75845
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))
//===---------------------------------------------------------------------===//