[PATCH] parallel loop metadata

[Pekka Jääskeläinen]

Hi,

The attached patch implements a simple mechanism to mark parallel
loops.

It uses two types of metadata:
llvm.loop.ignore_assumed_deps attached to the loop latch's
branch instruction and llvm.mem.parallel_loop_access attached to
all of the parallel loop's memory accesses.

Loop::isParallel() checks these. If llvm.loop.ignore_assumed_deps
is found, it ensures all the memory instructions inside the
loop body have the llvm.mem.parallel_loop_access attached before
returning true.

Test included for the LoopVectorizer that uses this info to parallelize
a strange looking loop which it otherwise skips completely.

Also included is a test that the parallel loop is converted to a
non-vectorizable one after reg2mem adds new memory instructions (without
the llvm.mem.parallel_loop_access metadata).

-- 
Pekka
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