Improve SLP code snippet

[lsandov1]

Summary

New C code snippet is more viable for SLP vectorization in most architectures.

[spatel]

llvm/docs/Vectorizers.rst

421–424

I understand that integer division is a poor example for vectorization because most targets can't handle it.
But what is the intent of changing 'int' to 'long' in this example? That change appears to prevent vectorization (for most x86 targets at least).

[lsandov1]

llvm/docs/Vectorizers.rst

421–424

I was biased by AVX2 in my example (4 longs fits a ymm register) but agree that 'int' is less intrusive and more generic for the proposed code snippet. I will change it.

[lsandov1]

s/long/int as suggested by @spatel

[spatel]

LGTM - this is definitely better than division, but it might be better yet to have a simpler example and show how it translates to IR.

[lsandov1]

@spatel please commit this change on my behalf. This is my first patch and I still do not have write access to the repo. Thanks

llvm/docs/Vectorizers.rst

 
 For example, the following function performs very similar operations on its
 inputs (a1, b1) and (a2, b2). The basic-block vectorizer may combine these
 into vector operations.
 
 .. code-block:: c++
 
   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;
+    A[0] = a1*(a1 + b1);
+    A[1] = a2*(a2 + b2);
+    A[2] = a1*(a1 + b1);
+    A[3] = a2*(a2 + b2);
   }
 
 The SLP-vectorizer processes the code bottom-up, across basic blocks, in search of scalars to combine.
 
 Usage
 ------
 
 The SLP Vectorizer is enabled by default, but it can be disabled
 through clang using the command line flag:
 
 .. code-block:: console
 
    $ clang -fno-slp-vectorize file.c