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Diffstat (limited to 'llvm/docs/Vectorizers.rst')
| -rw-r--r-- | llvm/docs/Vectorizers.rst | 30 |
1 files changed, 15 insertions, 15 deletions
diff --git a/llvm/docs/Vectorizers.rst b/llvm/docs/Vectorizers.rst index 98f1451d0de..4a85a7ee6db 100644 --- a/llvm/docs/Vectorizers.rst +++ b/llvm/docs/Vectorizers.rst @@ -13,7 +13,7 @@ The Loop Vectorizer =================== Usage -^^^^^^ +----- LLVM's Loop Vectorizer is now available and will be useful for many people. It is not enabled by default, but can be enabled through clang using the @@ -30,13 +30,13 @@ will only vectorize loops that do not require a major increase in code size. We plan to enable the Loop Vectorizer by default as part of the LLVM 3.3 release. Features -^^^^^^^^^ +-------- The LLVM Loop Vectorizer has a number of features that allow it to vectorize complex loops. Loops with unknown trip count ------------------------------- +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ The Loop Vectorizer supports loops with an unknown trip count. In the loop below, the iteration ``start`` and ``finish`` points are unknown, @@ -53,7 +53,7 @@ a scalar copy of the loop increases the code size. } Runtime Checks of Pointers --------------------------- +^^^^^^^^^^^^^^^^^^^^^^^^^^ In the example below, if the pointers A and B point to consecutive addresses, then it is illegal to vectorize the code because some elements of A will be @@ -75,7 +75,7 @@ of the loop is executed. Reductions --------------------------- +^^^^^^^^^^ In this example the ``sum`` variable is used by consecutive iterations of the loop. Normally, this would prevent vectorization, but the vectorizer can @@ -94,7 +94,7 @@ reduction operations, such as addition, multiplication, XOR, AND and OR. } Inductions --------------------------- +^^^^^^^^^^ In this example the value of the induction variable ``i`` is saved into an array. The Loop Vectorizer knows to vectorize induction variables. @@ -107,7 +107,7 @@ array. The Loop Vectorizer knows to vectorize induction variables. } If Conversion --------------------------- +^^^^^^^^^^^^^ The Loop Vectorizer is able to "flatten" the IF statement in the code and generate a single stream of instructions. The Loop Vectorizer supports any @@ -125,7 +125,7 @@ nesting of IFs, ELSEs and even GOTOs. } Pointer Induction Variables ---------------------------- +^^^^^^^^^^^^^^^^^^^^^^^^^^^ This example uses the "accumulate" function of the standard c++ library. This loop uses C++ iterators, which are pointers, and not integer indices. @@ -139,7 +139,7 @@ this loop. This feature is important because many C++ programs use iterators. } Reverse Iterators --------------------------- +^^^^^^^^^^^^^^^^^ The Loop Vectorizer can vectorize loops that count backwards. @@ -151,7 +151,7 @@ The Loop Vectorizer can vectorize loops that count backwards. } Scatter / Gather ----------------- +^^^^^^^^^^^^^^^^ The Loop Vectorizer can vectorize code that becomes scatter/gather memory accesses. @@ -164,7 +164,7 @@ memory accesses. } Vectorization of Mixed Types ----------------------------- +^^^^^^^^^^^^^^^^^^^^^^^^^^^^ The Loop Vectorizer can vectorize programs with mixed types. The Vectorizer cost model can estimate the cost of the type conversion and decide if @@ -178,7 +178,7 @@ vectorization is profitable. } Vectorization of function calls -------------------------------- +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ The Loop Vectorize can vectorize intrinsic math functions. See the table below for a list of these functions. @@ -196,7 +196,7 @@ See the table below for a list of these functions. +-----+-----+---------+ Performance -^^^^^^^^^^^ +----------- This section shows the the execution time of Clang on a simple benchmark: `gcc-loops <http://llvm.org/viewvc/llvm-project/test-suite/trunk/SingleSource/UnitTests/Vectorizer/>`_. @@ -212,7 +212,7 @@ 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: @@ -222,7 +222,7 @@ through clang using the command line flag: $ clang -fslp-vectorize file.c Details -^^^^^^^ +------- The goal of basic-block vectorization (a.k.a. superword-level parallelism) is to combine similar independent instructions within simple control-flow regions |
