From ed5ec7b16a1cf13c0902114d623b77282f333739 Mon Sep 17 00:00:00 2001 From: Hans Wennborg Date: Wed, 26 Aug 2015 18:58:15 +0000 Subject: [PATCH] Polly subproject release notes By Tobias Grosser! git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_37@246053 91177308-0d34-0410-b5e6-96231b3b80d8 --- docs/ReleaseNotes.rst | 108 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 108 insertions(+) diff --git a/docs/ReleaseNotes.rst b/docs/ReleaseNotes.rst index 98a21649f2d..417971748c9 100644 --- a/docs/ReleaseNotes.rst +++ b/docs/ReleaseNotes.rst @@ -246,6 +246,114 @@ Changes to the JIT APIs encouraged to try ORC out for their projects. (A good place to start is the new ORC tutorials under llvm/examples/kaleidoscope/orc). +Sub-project Status Update +========================= + +In addition to the core LLVM 3.7 distribution of production-quality compiler +infrastructure, the LLVM project includes sub-projects that use the LLVM core +and share the same distribution license. This section provides updates on these +sub-projects. + +Polly - The Polyhedral Loop Optimizer in LLVM +--------------------------------------------- + +`Polly `_ is a polyhedral loop optimization +infrastructure that provides data-locality optimizations to LLVM-based +compilers. When compiled as part of clang or loaded as a module into clang, +it can perform loop optimizations such as tiling, loop fusion or outer-loop +vectorization. As a generic loop optimization infrastructure it allows +developers to get a per-loop-iteration model of a loop nest on which detailed +analysis and transformations can be performed. + +Changes since the last release: + +* isl imported into Polly distribution + +`isl `_, the math library Polly uses, has been +imported into the source code repository of Polly and is now distributed as part +of Polly. As this was the last external library dependency of Polly, Polly can +now be compiled right after checking out the Polly source code without the need +for any additional libraries to be pre-installed. + +* Small integer optimization of isl + +The MIT licensed imath backend using in `isl `_ for +arbitrary width integer computations has been optimized to use native integer +operations for the common case where the operands of a computation fit into 32 +bit and to only fall back to large arbitrary precision integers for the +remaining cases. This optimization has greatly improved the compile-time +performance of Polly, both due to faster native operations also due to a +reduction in malloc traffic and pointer indirections. As a result, computations +that use arbitrary precision integers heavily have been speed up by almost 6x. +As a result, the compile-time of Polly on the Polybench test kernels in the LNT +suite has been reduced by 20% on average with compile time reductions between +9-43%. + +* Schedule Trees + +Polly now uses internally so-called > Schedule Trees < to model the loop +structure it optimizes. Schedule trees are an easy to understand tree structure +that describes a loop nest using integer constraint sets to keep track of +execution constraints. It allows the developer to use per-tree-node operations +to modify the loop tree. Programatic analysis that work on the schedule tree +(e.g., as dependence analysis) also show a visible speedup as they can exploit +the tree structure of the schedule and need to fall back to ILP based +optimization problems less often. Section 6 of `Polyhedral AST generation is +more than scanning polyhedra +`_ gives a detailed +explanation of this schedule trees. + +* Scalar and PHI node modeling - Polly as an analysis + +Polly now requires almost no preprocessing to analyse LLVM-IR, which makes it +easier to use Polly as a pure analysis pass e.g. to provide more precise +dependence information to non-polyhedral transformation passes. Originally, +Polly required the input LLVM-IR to be preprocessed such that all scalar and +PHI-node dependences are translated to in-memory operations. Since this release, +Polly has full support for scalar and PHI node dependences and requires no +scalar-to-memory translation for such kind of dependences. + +* Modeling of modulo and non-affine conditions + +Polly can now supports modulo operations such as A[t%2][i][j] as they appear +often in stencil computations and also allows data-dependent conditional +branches as they result e.g. from ternary conditions ala A[i] > 255 ? 255 : +A[i]. + +* Delinearization + +Polly now support the analysis of manually linearized multi-dimensional arrays +as they result form macros such as +"#define 2DARRAY(A,i,j) (A.data[(i) * A.size + (j)]". Similar constructs appear +in old C code written before C99, C++ code such as boost::ublas, LLVM exported +from Julia, Matlab generated code and many others. Our work titled +`Optimistic Delinearization of Parametrically Sized Arrays +`_ gives details. + +* Compile time improvements + +Pratik Bahtu worked on compile-time performance tuning of Polly. His work +together with the support for schedule trees and the small integer optimization +in isl notably reduced the compile time. + +* Increased compute timeouts + +As Polly's compile time has been notabily improved, we were able to increase +the compile time saveguards in Polly. As a result, the default configuration +of Polly can now analyze larger loop nests without running into compile time +restrictions. + +* Export Debug Locations via JSCoP file + +Polly's JSCoP import/export format gained support for debug locations that show +to the user the source code location of detected scops. + +* Improved windows support + +The compilation of Polly on windows using cmake has been improved and several +visual studio build issues have been addressed. + +* Many bug fixes External Open Source Projects Using LLVM 3.7 ============================================ -- 2.40.0