maxjhandsome
/
llvm-project
forked from OSchip/llvm-project
1
0
Fork 0
Code Issues Pull Requests Packages Releases Wiki Activity

Docs: merge the description of the BB and SLP vectorizers and document the -fslp-vectorize-aggressive flag. 

llvm-svn: 179510
This commit is contained in:
Nadav Rotem 2013-04-15 05:53:23 +00:00
parent d4dcc003df
commit 57da1fdd55
1 changed files with 23 additions and 25 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

48
llvm/docs/Vectorizers.rst
View File

@ -292,25 +292,15 @@ And Linpack-pc with the same configuration. Result is Mflops, higher is better.
.. image:: linpack-pc.png
.. _bb-vectorizer:
.. _slp-vectorizer:
The Basic Block Vectorizer
==========================
Usage
------
The Basic Block Vectorizer is not enabled by default, but it can be enabled
through clang using the command line flag:
.. code-block:: console
$ clang -fslp-vectorize file.c
The SLP Vectorizer
==================
Details
-------
The goal of basic-block vectorization (a.k.a. superword-level parallelism) is
The goal of SLP vectorization (a.k.a. superword-level parallelism) is
to combine similar independent instructions within simple control-flow regions
into vector instructions. Memory accesses, arithemetic operations, comparison
operations and some math functions can all be vectorized using this technique
@ -322,22 +312,30 @@ into vector operations.
.. code-block:: c++
int foo(int a1, int a2, int b1, int b2) {
int r1 = a1*(a1 + b1)/b1 + 50*b1/a1;
int r2 = a2*(a2 + b2)/b2 + 50*b2/a2;
return r1 + r2;
void foo(int a1, int a2, int b1, int b2, int *A) {
A[0] = a1*(a1 + b1)/b1 + 50*b1/a1;
A[1] = a2*(a2 + b2)/b2 + 50*b2/a2;
}
.. _slp-vectorizer:
Usage
------
The SLP Vectorizer
==========================
The SLP Vectorizer is not enabled by default, but it can be enabled
through clang using the command line flag:
.. code-block:: console
$ clang -fslp-vectorize file.c
LLVM has a second phase basic block vectorization phase
which is more compile-time intensive (The BB vectorizer). This optimization
can be enabled through clang using the command line flag:
.. code-block:: console
$ clang -fslp-vectorize-aggressive file.c
The SLP vectorizer (superword-level parallelism) is a new experimental
infrastructure for vectorizing code and rolling loops.
A major focus of the work on the SLP vectorizer is to make it fast and
flexible. It is designed as a library that can be used by other passes.
The SLP vectorizer is in early development stages but can already vectorize
and accelerate many programs in the LLVM test suite.