mirror of
https://github.com/RPCS3/llvm.git
synced 2025-01-19 08:24:12 +00:00
011536a1cc
Summary: ScalarEvolutionExpander assumes that the header block of a loop is a legal place to have a use for a phi node. This is true only for phis that are either in the header or dominate the header block, but it is not true for phi nodes that are strictly internal to the loop body. This change teaches ScalarEvolutionExpander to place uses of PHI nodes in the basic block the PHI nodes belong to. This is always legal, and `hoistIVInc` ensures that the said position dominates `IsomorphicInc`. Reviewers: atrick Subscribers: llvm-commits Differential Revision: http://reviews.llvm.org/D8311 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@232189 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))
//===---------------------------------------------------------------------===//