[PATCH] [AArch64] Generate tbz/tbnz when comparing against zero.

[Chad Rosier]

Hi t.p.northover, jmolloy,

This patch generates tbz/tbnz when comparing against zero.  The tbz/tbnz checks the sign bit to convert

add/sub w1, w1, w10
cmp w1, #0
b.lt .LBB0_0

to

adds/subs w1, w1, w10
tbnz w1, #31, .LBB0_0

Please have a look.

On an A53 processor this improves the following benchmarks:
office_suite/OAv2mark +3%
 office_suite/rotatev2data* +6-10%

I also saw improvements in spec2000 parser, vortex, and vpr, but just barely above noise, so I wouldn't bank on them.  These numbers were based on the community mainline.

 Chad

http://reviews.llvm.org/D4440

Files:
  lib/Target/AArch64/AArch64ISelLowering.cpp
  test/CodeGen/AArch64/tbz-tbnz.ll
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