With the option -outline-optional-branches, LLVM will place optional
branches out of line (more details on r231230).
With this patch, this is not done for short optional branches. A short
optional branch is a branch containing a single block with an
instruction count below a certain threshold (defaulting to 3). Still
everything is guarded under -outline-optional-branches).
Outlining a short branch can't significantly improve code locality. It
can however decrease performance because of the additional jmp and in
cases where the optional branch is hot. This fixes a compile time
regression I have observed in a benchmark.
Review: http://reviews.llvm.org/D8108
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@232802 91177308-0d34-0410-b5e6-96231b3b80d8
In a CFG with the edges A->B->C and A->C, B is an optional branch.
LLVM's default behavior is to lay the blocks out naturally, i.e. A, B,
C, in order to improve code locality and fallthroughs. However, if a
function contains many of those optional branches only a few of which
are taken, this leads to a lot of unnecessary icache misses. Moving B
out of line can work around this.
Review: http://reviews.llvm.org/D7719
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@231230 91177308-0d34-0410-b5e6-96231b3b80d8
