tree 670cb79eab73097b0958f4ee9a760b1bddb6c64d
parent 818d98eb563ad5d7293b8b5c40f3dabf745e611f
author buzbee <buzbee@google.com> 1360714783 -0800
committer buzbee <buzbee@google.com> 1360879914 -0800

Add "select" detection to common frontend

dx produces a somewhat ugly code pattern for selects:

   foo = (condition) ? true : false;

There is no select Dex opcode, so this turns into:

    IF_EQ v0, L1
    CONST_4 V2, #0
L2:
    <rejoin>
.
.
L1:
    CONST_4 V2, #1
    GOTO L2

...  or ...

   foo = (condition) ? bar1 : bar2;

    IF_EQ v0, L1
    MOVE V2, V3
L2:
    <rejoin>
.
.
L1:
    MOVE V2, V4
    GOTO L2

Not only do we end up with excessive branching (and, unless we
something special, really poor code layout), but the compilers
generally drop down a suspend check on backwards branches - which is
completely unnecessary in the "GOTO L2" case above.  There are ~2100
instances of the simplest variants of this pattern in the framework.
With this new optimization, boot.oat size is reduced by 90K bytes
and one of our standard benchmarks got an 8% pop.

This CL adds a select detection operation to the common frontend's
BasicBlock optimization pass, and introduces a new extended MIR
opcode: kMirOpSelect.

Change-Id: I06249956ba21afb0ed5cdd35019ac87cd063a17b