Files
llvm/lib/Analysis
Roman Lebedev 07c1e2bdfa [CostModel] Model all extractvalues as free.
Summary:
As disscussed in https://reviews.llvm.org/D65148#1606412,
`extractvalue` don't actually generate any code,
so we should treat them as free.

Reviewers: craig.topper, RKSimon, jnspaulsson, greened, asb, t.p.northover, jmolloy, dmgreen

Reviewed By: jmolloy

Subscribers: javed.absar, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D66098

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@370339 91177308-0d34-0410-b5e6-96231b3b80d8
2019-08-29 11:50:30 +00:00
..
2019-08-09 13:56:29 +00:00
2019-05-31 10:14:04 +00:00

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))

//===---------------------------------------------------------------------===//