Files
llvm/lib/Analysis
Sanjay Patel 43b05ab4b9 [InstSimplify] fold fma/fmuladd with a NaN or undef operand
This is intended to be similar to the constant folding results from
D67446
and earlier, but not all operands are constant in these tests, so the
responsibility for folding is left to InstSimplify.

Differential Revision: https://reviews.llvm.org/D67721

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@373455 91177308-0d34-0410-b5e6-96231b3b80d8
2019-10-02 12:12:02 +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))

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