mirror of
https://github.com/RPCS3/llvm.git
synced 2026-07-23 12:15:39 -04:00
Max Kazantsev
8e59cd1915
This patch relaxes overconservative checks on whether or not we could write memory before we execute an instruction. This allows us to hoist guards out of loops even if they are not in the header block. Differential Revision: https://reviews.llvm.org/D50891 Reviewed By: fedor.sergeev git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@346643 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))
//===---------------------------------------------------------------------===//