commit 4a0e84a1be52d9a57574de0421d9aa38522a0b71
author Keith Randall <khr@golang.org> Thu Jan 05 13:02:44 2023 -0800
committer Keith Randall <khr@google.com> Thu Jan 26 00:07:40 2023 +0000
tree a18d6a828916cc9f5a194b5cec073d9b709a3c2b
parent 2c7856087a7b3864284f908c0a091fd5af419d03

cmd/compile: improve register overwrite decision for resultInArg0 ops

When we're compiling a resultInArg0 op, we need to clobber the
register containing the input value. So we first make a register copy
of the input value. We can then clobber either of the two registers
the value is in and still have the original input value in a register
for future uses.

Before this CL, we always clobbered the original, not the copy.
But that's not always the right decision - if the original is already
in a specific register that it needs to be in later (typically, a
return value register), clobber the copy instead.

This optimization can remove a mov instruction. It saves 1376 bytes
of instructions in cmd/go.

Redo of CL 460656, reverted at CL 463475, with a fix for s390x.

The new code just ensures that the copied value is in a register
which is a valid input register for the instruction.

Change-Id: Id570b8a60a6d2da9090de80a90b6bb0266e9e38a
Reviewed-on: https://go-review.googlesource.com/c/go/+/463221
Auto-Submit: Keith Randall <khr@golang.org>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>