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

Review URL: https://codereview.chromium.org/1118353005