Subzero: Use a setcc sequence for better icmp lowering.

Subzero: Use a setcc sequence for better icmp lowering.

For an example like:
  %a = icmp eq i32 %b, %c

The original icmp lowering sequence for i8/i16/i32 was something like:

  cmpl b, c
  movb 1, a
  je label
  movb 0, a
label:

The improved sequence is:
  cmpl b, c
  sete a

In O2 mode, this doesn't help when successive compare/branch instructions are fused, but it does help when the boolean result needs to be saved and later used.

BUG= none
R=jvoung@chromium.org

Committed: https://gerrit.chromium.org/gerrit/gitweb?p=native_client/pnacl-subzero.git;a=commit;h=f48b320c64ccd0ace2b873fd54471e0938c2f0ce

[Jim Stichnoth, 2015-05-01 21:17:16]

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

[Jim Stichnoth, 2015-05-01 21:23:18]

This makes each Spec2k component about 2% smaller, but has little measurable
effect on performance.

[jvoung (off chromium), 2015-05-04 16:28:21]

Cool -- LGTM

[Jim Stichnoth, 2015-05-04 17:22:22]

Committed patchset #2 (id:20001) manually as
f48b320c64ccd0ace2b873fd54471e0938c2f0ce (tree was closed).