David Bolvansky 05bda8b4e5 Annotate return values of allocation functions with dereferenceable_or_null
Summary:
Example
define dso_local noalias i8* @_Z6maixxnv() local_unnamed_addr #0 {
entry:
  %call = tail call noalias dereferenceable_or_null(64) i8* @malloc(i64 64) #6
  ret i8* %call
}


Reviewers: jdoerfert

Reviewed By: jdoerfert

Subscribers: aaron.ballman, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D66651

llvm-svn: 370168
2019-08-28 08:28:20 +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))

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