Subzero: Improve lowering of rematerializable call args.

Subzero: Improve lowering of rematerializable call args.

Normally, if a call argument is a rematerializable Variable, it is rematerialized into a GPR (via the "lea" instruction) and then written into the appropriate arg space.

This is appropriate for arguments passed on the stack, but for register arguments, it forces an unnecessary copy through another register.

This CL allows that intermediate register copy to be removed.

The resulting code looks cleaner, but it is unlikely to have much effect on performance - there really aren't register pressure issues because lots of scratch registers are available right before the call (which kills all scratch registers).

BUG= none
R=jpp@chromium.org

Committed: https://gerrit.chromium.org/gerrit/gitweb?p=native_client/pnacl-subzero.git;a=commit;h=e450656d45ef91dc3a1cf51eda0e13fffdb7ff7d

[Jim Stichnoth, 2016-06-17 21:20:54]

Description was changed from

==========
Subzero: Improve lowering of rematerializable call args.

BUG= none
==========

to

==========
Subzero: Improve lowering of rematerializable call args.

Normally, if a call argument is a rematerializable Variable, it is
rematerialized into a GPR (via the "lea" instruction) and then written into the
appropriate arg space.

This is appropriate for arguments passed on the stack, but for register
arguments, it forces an unnecessary copy through another register.

This CL allows that intermediate register copy to be removed.

BUG= none
==========

[Jim Stichnoth, 2016-06-17 21:27:12]

Description was changed from

==========
Subzero: Improve lowering of rematerializable call args.

Normally, if a call argument is a rematerializable Variable, it is
rematerialized into a GPR (via the "lea" instruction) and then written into the
appropriate arg space.

This is appropriate for arguments passed on the stack, but for register
arguments, it forces an unnecessary copy through another register.

This CL allows that intermediate register copy to be removed.

BUG= none
==========

to

==========
Subzero: Improve lowering of rematerializable call args.

Normally, if a call argument is a rematerializable Variable, it is
rematerialized into a GPR (via the "lea" instruction) and then written into the
appropriate arg space.

This is appropriate for arguments passed on the stack, but for register
arguments, it forces an unnecessary copy through another register.

This CL allows that intermediate register copy to be removed.

The resulting code looks cleaner, but it is unlikely to have much effect on
performance - there really aren't register pressure issues because lots of
scratch registers are available right before the call (which kills all scratch
registers).

BUG= none
==========

[Jim Stichnoth, 2016-06-17 21:59:00]

stichnot@chromium.org changed reviewers:
+ eholk@chromium.org, jpp@chromium.org, kschimpf@google.com, manasijm@google.com

[John, 2016-06-20 13:41:48]

lgtm

[Jim Stichnoth, 2016-06-20 13:44:13]

Description was changed from

==========
Subzero: Improve lowering of rematerializable call args.

Normally, if a call argument is a rematerializable Variable, it is
rematerialized into a GPR (via the "lea" instruction) and then written into the
appropriate arg space.

This is appropriate for arguments passed on the stack, but for register
arguments, it forces an unnecessary copy through another register.

This CL allows that intermediate register copy to be removed.

The resulting code looks cleaner, but it is unlikely to have much effect on
performance - there really aren't register pressure issues because lots of
scratch registers are available right before the call (which kills all scratch
registers).

BUG= none
==========

to

==========
Subzero: Improve lowering of rematerializable call args.

Normally, if a call argument is a rematerializable Variable, it is
rematerialized into a GPR (via the "lea" instruction) and then written into the
appropriate arg space.

This is appropriate for arguments passed on the stack, but for register
arguments, it forces an unnecessary copy through another register.

This CL allows that intermediate register copy to be removed.

The resulting code looks cleaner, but it is unlikely to have much effect on
performance - there really aren't register pressure issues because lots of
scratch registers are available right before the call (which kills all scratch
registers).

BUG= none
R=jpp@chromium.org

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

[Jim Stichnoth, 2016-06-20 13:44:15]

Committed patchset #1 (id:1) manually as
e450656d45ef91dc3a1cf51eda0e13fffdb7ff7d (presubmit successful).