From 23aefe5e9232b973468680b673a2f14fc86d40a4 Mon Sep 17 00:00:00 2001 From: Dan Gohman Date: Mon, 28 Sep 2009 18:38:53 +0000 Subject: Create a README.txt for lib/Analysis, and add an entry. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@83001 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Analysis/README.txt | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) create mode 100644 lib/Analysis/README.txt (limited to 'lib/Analysis/README.txt') diff --git a/lib/Analysis/README.txt b/lib/Analysis/README.txt new file mode 100644 index 0000000000..c401090272 --- /dev/null +++ b/lib/Analysis/README.txt @@ -0,0 +1,18 @@ +Analysis Opportunities: + +//===---------------------------------------------------------------------===// + +In test/Transforms/LoopStrengthReduce/quadradic-exit-value.ll, the +ScalarEvolution expression for %r is this: + + {1,+,3,+,2} + +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. + +//===---------------------------------------------------------------------===// -- cgit v1.2.3