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New GCC options for loop vectorization

Currently -ftree-vectorize turns on both loop and slp vectorizations,
but there is no simple way to turn on loop vectorization alone. The
logic for default O3 setting is also complicated.

In this patch, two new options are introduced:

1) -ftree-loop-vectorize

This option is used to turn on loop vectorization only. option
-ftree-slp-vectorize also becomes a first class citizen, and no funny
business of Init(2) is needed.  With this change, -ftree-vectorize
becomes a simple alias to -ftree-loop-vectorize +

For instance, to turn on only slp vectorize at O3, the old way is:

     -O3 -fno-tree-vectorize -ftree-slp-vectorize

With the new change it becomes:

    -O3 -fno-loop-vectorize

To turn on only loop vectorize at O2, the old way is

    -O2 -ftree-vectorize -fno-slp-vectorize

The new way is

    -O2 -ftree-loop-vectorize

2) -ftree-vect-loop-peeling

This option is used to turn on/off loop peeling for alignment.  In the
long run, this should be folded into the cheap cost model proposed by
Richard.  This option is also useful in scenarios where peeling can
introduce runtime problems:  which happens to be
common in practice.

Patch attached. Compiler boostrapped. Ok after testing?



Attachment: vect_new_opts.txt
Description: Text document

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