mirror of
https://github.com/llvm/llvm-project.git
synced 2025-05-16 17:26:04 +00:00
6f3511a01a
There's a potential motivating case to increase this limit in PR47191: http://bugs.llvm.org/PR47191 But first we should make it less hacky. The limit in InstCombine is directly tied to this value because an increase there can cause asserts in the underlying value tracking calls if not changed together. The usage in VectorUtils is independent, but the comment suggests that we should use the same value unless there's a known reason to diverge. There are similar limits in codegen analysis, but I think we should leave those independent in case we intentionally want the optimization power/cost to be different there. Differential Revision: https://reviews.llvm.org/D86113
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))
//===---------------------------------------------------------------------===//