[MachineScheduler] Fix for PR21807: minor code difference building with/without -g.

This patch fixes the issue reported as PR21807. There was a minor difference
in the generated code depending on the -g flag.

The cause was that with -g the machine scheduler used a different
scheduling strategy. This decision was based on the number of instructions
in a schedule region and included debug instructions in that count.

This patch fixes the issue in MISched and provides a test.

Patch by Russell Gallop!


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224118 91177308-0d34-0410-b5e6-96231b3b80d8
This patch recognizes (+ (+ v0, v1) (+ v2, v3)), reorders them for bundling into vector of loads,
and vectorizes it. 
 
 Test case :
 
       float hadd(float* a) {
           return (a[0] + a[1]) + (a[2] + a[3]);
        }
 
 
 AArch64 assembly before patch :
 
        ldp	s0, s1, [x0]
 	ldp	s2, s3, [x0, #8]
 	fadd	s0, s0, s1
 	fadd	s1, s2, s3
 	fadd	s0, s0, s1
 	ret
 
 AArch64 assembly after patch :
 
        ldp	d0, d1, [x0]
 	fadd	v0.2s, v0.2s, v1.2s
 	faddp	s0, v0.2s
 	ret

Reviewed Link : http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20141208/248531.html



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224119 91177308-0d34-0410-b5e6-96231b3b80d8