Move the frame lowering constructors out of line to avoid circular

[oota-llvm.git] / docs / Vectorizers.rst

diff --git a/docs/Vectorizers.rst b/docs/Vectorizers.rst
index 693a148fa547aaefedc28fe920dacfd216833155..887ccaa8f8151b99d145afba0235bde5f58ad835 100644 (file)
--- a/docs/Vectorizers.rst
+++ b/docs/Vectorizers.rst
@@ -6,12 +6,14 @@ Auto-Vectorization in LLVM
    :local:
 
 LLVM has two vectorizers: The :ref:`Loop Vectorizer <loop-vectorizer>`,
-which operates on Loops, and the :ref:`Basic Block Vectorizer
-<bb-vectorizer>`, which optimizes straight-line code. These vectorizers
+which operates on Loops, and the :ref:`SLP Vectorizer
+<slp-vectorizer>`. These vectorizers
 focus on different optimization opportunities and use different techniques.
-The BB vectorizer merges multiple scalars that are found in the code into
-vectors while the Loop Vectorizer widens instructions in the original loop
-to operate on multiple consecutive loop iterations.
+The SLP vectorizer merges multiple scalars that are found in the code into
+vectors while the Loop Vectorizer widens instructions in loops
+to operate on multiple consecutive iterations.
+
+Both the Loop Vectorizer and the SLP Vectorizer are enabled by default.
 
 .. _loop-vectorizer:
 
@@ -21,8 +23,8 @@ The Loop Vectorizer
 Usage
 -----
 
-LLVM's Loop Vectorizer is now enabled by default for -O3.
-The vectorizer can be disabled using the command line:
+The Loop Vectorizer is enabled by default, but it can be disabled
+through clang using the command line flag:
 
 .. code-block:: console
 
@@ -180,11 +182,14 @@ that scatter/gathers memory.
 
 .. code-block:: c++
 
-  int foo(int *A, int *B, int n, int k) {
-    for (int i = 0; i < n; ++i)
-      A[i*7] += B[i*k];
+  int foo(int * A, int * B, int n) {
+    for (intptr_t i = 0; i < n; ++i)
+        A[i] += B[i * 4];
   }
 
+In many situations the cost model will inform LLVM that this is not beneficial
+and LLVM will only vectorize such code if forced with "-mllvm -force-vector-width=#".
+
 Vectorization of Mixed Types
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
@@ -301,10 +306,9 @@ Details
 -------
 
 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
-(subject to the capabilities of the target architecture).
+to combine similar independent instructions
+into vector instructions. Memory accesses, arithmetic operations, comparison
+operations, PHI-nodes, can all be vectorized using this technique.
 
 For example, the following function performs very similar operations on its
 inputs (a1, b1) and (a2, b2). The basic-block vectorizer may combine these
@@ -317,18 +321,19 @@ into vector operations.
     A[1] = a2*(a2 + b2)/b2 + 50*b2/a2;
   }
 
+The SLP-vectorizer processes the code bottom-up, across basic blocks, in search of scalars to combine.
 
 Usage
 ------
 
-The SLP Vectorizer is not enabled by default, but it can be enabled
+The SLP Vectorizer is enabled by default, but it can be disabled
 through clang using the command line flag:
 
 .. code-block:: console
 
-   $ clang -fslp-vectorize file.c
+   $ clang -fno-slp-vectorize file.c
 
-LLVM has a second phase basic block vectorization phase
+LLVM has a second 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:
 
@@ -336,24 +341,3 @@ can be enabled through clang using the command line flag:
 
    $ clang -fslp-vectorize-aggressive file.c
 
-
-The SLP vectorizer is in early development stages but can already vectorize
-and accelerate many programs in the LLVM test suite.
-
-=======================   ============
-Benchmark Name              Gain
-=======================   ============
-Misc/flops-7               -32.70%
-Misc/matmul_f64_4x4        -23.23%
-Olden/power                -21.45%
-Misc/flops-4               -14.90%
-ASC_Sequoia/AMGmk          -13.85%
-TSVC/LoopRerolling-flt     -11.76%
-Misc/flops-6               -9.70%
-Misc/flops-5               -8.54%
-Misc/flops                 -8.12%
-TSVC/NodeSplitting-dbl     -6.96%
-Misc-C++/sphereflake       -6.74%
-Ptrdist/yacr2              -6.31%
-=======================   ============
-