Subzero: Legalize FP constants directly into memory operands.

Subzero: Legalize FP constants directly into memory operands.

Previously, the legalize() function would always force a floating point constant into an xmm register before it could be used in an instruction.  This uses an extra register unnecessarily when the instruction allows a memory operand for that operand.

We improve this by lowering the FP constant operand to an OperandX8632Mem that wraps a ConstantRelocatable representing the label for the constant pool entry, e.g. [.L$float$0].  (This may end up being copied into an xmm register if the instruction doesn't allow a memory operand for that operand.)

BUG= https://code.google.com/p/nativeclient/issues/detail?id=4095
R=jvoung@chromium.org

Committed: https://gerrit.chromium.org/gerrit/gitweb?p=native_client/pnacl-subzero.git;a=commit;h=03ffa5853606f11f470baa459ead04dfa1c06ec5

[Jim Stichnoth, 2015-06-04 06:26:19]

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

[jvoung (off chromium), 2015-06-04 16:18:48]

lgtm

[Jim Stichnoth, 2015-06-04 16:25:14]

Committed patchset #1 (id:1) manually as
03ffa5853606f11f470baa459ead04dfa1c06ec5 (presubmit successful).