diff options
| author | Chandler Carruth <chandlerc@gmail.com> | 2012-12-14 13:37:17 +0000 |
|---|---|---|
| committer | Chandler Carruth <chandlerc@gmail.com> | 2012-12-14 13:37:17 +0000 |
| commit | ff038d7c73004175aeb9f0cb2c2507d2b0fc646b (patch) | |
| tree | a5433d0e1609bf9a27d33a4505a1b365e442730d /docs/ReleaseNotes.rst | |
| parent | b1c83058a47b1ebeffdb2aac5a2229892e80f81f (diff) | |
| download | llvm-ff038d7c73004175aeb9f0cb2c2507d2b0fc646b.tar.gz llvm-ff038d7c73004175aeb9f0cb2c2507d2b0fc646b.tar.bz2 llvm-ff038d7c73004175aeb9f0cb2c2507d2b0fc646b.tar.xz | |
Add a rough draft of some content about the new SROA. I'll try to proof
read this and clean it up tomorrow, but hopefully it's a good
placeholder.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@170196 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'docs/ReleaseNotes.rst')
| -rw-r--r-- | docs/ReleaseNotes.rst | 16 |
1 files changed, 15 insertions, 1 deletions
diff --git a/docs/ReleaseNotes.rst b/docs/ReleaseNotes.rst index 486074914b..31c567b33a 100644 --- a/docs/ReleaseNotes.rst +++ b/docs/ReleaseNotes.rst @@ -351,7 +351,21 @@ We vectorize under the following loops: '``noalias``' and are checked at runtime. #. ... -SROA - We've re-written SROA to be significantly more powerful. +SROA - We've re-written SROA to be significantly more powerful and generate +code which is much more friendly to the rest of the optimization pipeline. +Previously this pass had scaling problems that required it to only operate on +relatively small aggregates, and at times it would mistakenly replace a large +aggregate with a single very large integer in order to make it a scalar SSA +value. The result was a large number of i1024 and i2048 values representing any +small stack buffer. These in turn slowed down many subsequent optimization +paths. + +The new SROA pass uses a different algorithm that allows it to only promote to +scalars the pieces of the aggregate actively in use. Because of this it doesn't +require any thresholds. It also always deduces the scalar values from the uses +of the aggregate rather than the specific LLVM type of the aggregate. These +features combine to both optimize more code with the pass but to improve the +compile time of many functions dramatically. #. Branch weight metadata is preseved through more of the optimizer. #. ... |