[go] cmd/compile: do not home mul/div results in HI/LO

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Gopher Robot (Gerrit)

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Jul 25, 2026, 9:25:02 AM (yesterday) Jul 25

to Jorropo, goph...@pubsubhelper.golang.org, golang-...@googlegroups.com, David Chase, Daniel McCarney, Keith Randall, Keith Randall, golang...@luci-project-accounts.iam.gserviceaccount.com, Martin Möhrmann, golang-co...@googlegroups.com

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Change information

Commit message:

cmd/compile: do not home mul/div results in HI/LO

On mips and mips64, multiply/divide results were tuple outputs in the
special HI/LO registers, and regalloc kept live values homed there.
Spilling such a value must route the data through REGTMP (there is no
direct store from HI/LO). When the stack frame is too large for a
16-bit offset, the assembler also materializes the spill slot address
in REGTMP:

	MOVV	LO, R23
	LUI	R23, $1
	DADDU	R23, R23, SP
	SD	R23, off(R23)

clobbering the value and silently storing SP+0x10000 instead.

Instead, make MULV/MULVU/DIVV/DIVVU (mips64) and MULT/MULTU/DIV/DIVU
(mips) produce their results in two general registers, moving out of
HI and LO as part of the op itself.

Since register-register moves do not depend on REGTMP it can't get
the dual use bug.

Fixes #80563

Change-Id: I2a0cb5ec7103ab2b0cbbeb67edd38ff5cb33bf77

Reviewed-on: https://go-review.googlesource.com/c/go/+/805420

Reviewed-by: Keith Randall <k...@golang.org>

LUCI-TryBot-Result: golang...@luci-project-accounts.iam.gserviceaccount.com <golang...@luci-project-accounts.iam.gserviceaccount.com>

Reviewed-by: Keith Randall <k...@google.com>

Reviewed-by: David Chase <drc...@google.com>

Auto-Submit: Jorropo <jorro...@gmail.com>

Files:

M src/cmd/compile/internal/mips/ssa.go
M src/cmd/compile/internal/mips64/ssa.go
M src/cmd/compile/internal/ssa/_gen/MIPS64Ops.go
M src/cmd/compile/internal/ssa/_gen/MIPSOps.go
M src/cmd/compile/internal/ssa/opGen.go
M src/cmd/internal/obj/mips/asm0.go

Change size: M

Delta: 6 files changed, 107 insertions(+), 62 deletions(-)

Branch: refs/heads/master

Submit Requirements:

Code-Review: +1 by Keith Randall, +2 by Keith Randall, +2 by David Chase
TryBots-Pass: LUCI-TryBot-Result+1 by golang...@luci-project-accounts.iam.gserviceaccount.com

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