tree eab102ea2daba7fc58b95b9f4b8b4752128407fd
parent f26ed07f53daf19b33e13b3a93f185320d7b9a8b
author James Cowgill <james.cowgill@mips.com> 1519834214 +0000
committer Andrew Bonventre <andybons@golang.org> 1524946858 +0000

[release-branch.go1.10] cmd/internal/obj/mips: load/store even float registers first

There is a bug in Octeon III processors where storing an odd floating
point register after it has recently been written to by a double
floating point operation will store the old value from before the double
operation (there are some extra details - the operation and store
must be a certain number of cycles apart). However, this bug does not
occur if the even register is stored first. Currently the bug only
happens on big endian because go always loads the even register first on
little endian.

Workaround the bug by always loading / storing the even floating point
register first. Since this is just an instruction reordering, it should
have no performance penalty. This follows other compilers like GCC which
will always store the even register first (although you do have to set
the ISA level to MIPS I to prevent it from using SDC1).

Fixes golang/go#24995

Change-Id: I5e73daa4d724ca1df7bf5228aab19f53f26a4976
Reviewed-on: https://go-review.googlesource.com/97735
Reviewed-by: Keith Randall <khr@golang.org>
(cherry picked from commit 423111081b87c6c4e61c4d94c94bfdf1853fa01f)
Reviewed-on: https://go-review.googlesource.com/110078
Run-TryBot: Andrew Bonventre <andybons@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>