cmd/internal/obj/mips: use LR as temporary register in RET

On mips/mips64, for non-leaf function, RET is assembled as
	MOV (SP), R4       // load saved LR
	ADD $framesize, SP
	JMP (R4)

This clobbers R4 unnecessarily. Use the link register as
temporary instead.

Probably for Go 1.11.

Change-Id: I2209db7be11074ed2e0e0829cace95ebfb709e9f
Reviewed-on: https://go-review.googlesource.com/79016
Run-TryBot: Austin Clements <austin@google.com>
Reviewed-by: Austin Clements <austin@google.com>

diff --git a/src/cmd/internal/obj/mips/obj0.go b/src/cmd/internal/obj/mips/obj0.go
index 477f5531cc0da5cb0ef42f887e762292594a7658..2b9f18c9422a098691310324a0de5062c481001d 100644 (file)
--- a/src/cmd/internal/obj/mips/obj0.go
+++ b/src/cmd/internal/obj/mips/obj0.go
@@ -495,10 +495,7 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
                        p.From.Offset = 0
                        p.From.Reg = REGSP
                        p.To.Type = obj.TYPE_REG
-                       p.To.Reg = REG_R4
-                       if retSym != nil { // retjmp from non-leaf, need to restore LINK register
-                               p.To.Reg = REGLINK
-                       }
+                       p.To.Reg = REGLINK
 
                        if autosize != 0 {
                                q = c.newprog()
@@ -524,7 +521,7 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
                        } else {
                                q1.To.Type = obj.TYPE_MEM
                                q1.To.Offset = 0
-                               q1.To.Reg = REG_R4
+                               q1.To.Reg = REGLINK
                        }
                        q1.Mark |= BRANCH
                        q1.Spadj = +autosize