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author | Dan Gohman <gohman@apple.com> | 2009-09-28 18:38:53 +0000 |
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committer | Dan Gohman <gohman@apple.com> | 2009-09-28 18:38:53 +0000 |
commit | 23aefe5e9232b973468680b673a2f14fc86d40a4 (patch) | |
tree | 564db651a69ddf9755dd72f3384f2429a6e0b953 /lib/Analysis/README.txt | |
parent | 3168b79c1c16333d17295c44f9157c8321ec6235 (diff) | |
download | llvm-23aefe5e9232b973468680b673a2f14fc86d40a4.tar.gz llvm-23aefe5e9232b973468680b673a2f14fc86d40a4.tar.bz2 llvm-23aefe5e9232b973468680b673a2f14fc86d40a4.tar.xz |
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
Diffstat (limited to 'lib/Analysis/README.txt')
-rw-r--r-- | lib/Analysis/README.txt | 18 |
1 files changed, 18 insertions, 0 deletions
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}<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. + +//===---------------------------------------------------------------------===// |