mirror of
https://github.com/c64scene-ar/llvm-6502.git
synced 2025-03-17 05:31:32 +00:00
e11d1d2c31
Summary: Scalar evolution does not propagate the non-wrapping flags to values that are derived from a non-wrapping induction variable because the non-wrapping property could be flow-sensitive. This change is a first attempt to establish the non-wrapping property in some simple cases. The main idea is to look through the operations defining the pointer. As long as we arrive to a non-wrapping AddRec via a small chain of non-wrapping instruction, the pointer should not wrap either. I believe that this essentially is what Andy described in http://article.gmane.org/gmane.comp.compilers.llvm.cvs/220731 as the way forward. Reviewers: aschwaighofer, nadav, sanjoy, atrick Reviewed By: atrick Subscribers: llvm-commits Differential Revision: http://reviews.llvm.org/D10472 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@240798 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))
//===---------------------------------------------------------------------===//