Inline memcpy for small constant sizes.

Inline memcpy for small constant sizes.

Combined with memset inlining, this has shown an improvement of over 11% on
the eon benchmark. This the only C++ program in spec2k and it seems C++
programs have a significantly larger number of memset/memcpy calls. Other
benchmarks also showed improvement of ~5% (perlbmk, parser) while most had
a 1-2% improvement.

This commit also includes a refactoring of lowerMemset which is much more
readable and also removed the fake use of the destination pointer register.

BUG=
R=jvoung@chromium.org, stichnot@chromium.org

Committed: https://gerrit.chromium.org/gerrit/gitweb?p=native_client/pnacl-subzero.git;a=commit;h=9df4a379ebdb2f2200ec7f65017bd9fc8544794b

[ascull, 2015-08-06 22:28:02]

ascull@google.com changed reviewers:
+ jvoung@chromium.org, stichnot@chromium.org

[Jim Stichnoth, 2015-08-07 15:13:32]

LGTM, though it looks like there's a lot of commonality between memset and
memcpy.

Once you complete memset, maybe you'll look at refactoring opportunities across
the 3 implementations?

[jvoung (off chromium), 2015-08-07 15:37:08]

LGTM too

https://codereview.chromium.org/1279833005/diff/1/tests_lit/llvm2ice_tests/na...
File tests_lit/llvm2ice_tests/nacl-mem-intrinsics.ll (right):

https://codereview.chromium.org/1279833005/diff/1/tests_lit/llvm2ice_tests/na...
tests_lit/llvm2ice_tests/nacl-mem-intrinsics.ll:148: ; TODO(jvoung) -- if we
want to be clever, we can do memset without a function
"we can do memset" -> "we can do memmove"

https://codereview.chromium.org/1279833005/diff/1/tests_lit/llvm2ice_tests/na...
tests_lit/llvm2ice_tests/nacl-mem-intrinsics.ll:251: ; CHECK-LABEL:
test_memset_const_val_len_3
Could you also add a test for len == 3, but val == 0? There was some refactoring
in the code where you moved the len == 3 check lower. It looked right, but
probably good to have a test for that in case of more refactoring.

[ascull, 2015-08-07 16:19:39]

Committed patchset #1 (id:1) manually as
9df4a379ebdb2f2200ec7f65017bd9fc8544794b (presubmit successful).