cmd/compile, cmd/internal/obj/ppc64: mark unsafe points

We'll use CTR as a scratch register for call injection. Mark code
sequences that use CTR as unsafe for async preemption. Currently
it is only used in LoweredZero and LoweredMove. It is unfortunate
that they are nonpreemptible. But I think it is still better than
using LR for call injection and marking all leaf functions
nonpreemptible.

Also mark the prologue of large frame functions nonpreemptible,
as we write below SP.

Change-Id: I05a75431499f3f4b2f23651a7b17f7fcf2afbe06
Reviewed-on: https://go-review.googlesource.com/c/go/+/203823
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

src/cmd/compile/internal/ssa/gen/PPC64Ops.go

@@ -447,6 +447,7 @@ func init() {
 			clobberFlags:   true,
 			typ:            "Mem",
 			faultOnNilArg0: true,
+			unsafePoint:    true,
 		},
 		// R31 is temp register
 		// Loop code:
@@ -493,6 +494,7 @@ func init() {
 			typ:            "Mem",
 			faultOnNilArg0: true,
 			faultOnNilArg1: true,
+			unsafePoint:    true,
 		},
 
 		{name: "LoweredAtomicStore8", argLength: 3, reg: gpstore, typ: "Mem", aux: "Int64", faultOnNilArg0: true, hasSideEffects: true},

src/cmd/compile/internal/ssa/opGen.go

@@ -24566,6 +24566,7 @@ var opcodeTable = [...]opInfo{
 		argLen:         2,
 		clobberFlags:   true,
 		faultOnNilArg0: true,
+		unsafePoint:    true,
 		reg: regInfo{
 			inputs: []inputInfo{
 				{0, 8}, // R3
@@ -24580,6 +24581,7 @@ var opcodeTable = [...]opInfo{
 		clobberFlags:   true,
 		faultOnNilArg0: true,
 		faultOnNilArg1: true,
+		unsafePoint:    true,
 		reg: regInfo{
 			inputs: []inputInfo{
 				{0, 8},  // R3

src/cmd/internal/obj/ppc64/obj9.go

@@ -702,6 +702,8 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 					// Store link register before decrementing SP, so if a signal comes
 					// during the execution of the function prologue, the traceback
 					// code will not see a half-updated stack frame.
+					// This sequence is not async preemptible, as if we open a frame
+					// at the current SP, it will clobber the saved LR.
 					q = obj.Appendp(q, c.newprog)
 					q.As = AMOVD
 					q.Pos = p.Pos
@@ -710,6 +712,8 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 					q.To.Type = obj.TYPE_REG
 					q.To.Reg = REG_R29 // REGTMP may be used to synthesize large offset in the next instruction
 
+					q = c.ctxt.StartUnsafePoint(q, c.newprog)
+
 					q = obj.Appendp(q, c.newprog)
 					q.As = AMOVD
 					q.Pos = p.Pos
@@ -727,6 +731,9 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 					q.To.Type = obj.TYPE_REG
 					q.To.Reg = REGSP
 					q.Spadj = +autosize
+
+					q = c.ctxt.EndUnsafePoint(q, c.newprog, -1)
+
 				}
 			} else if c.cursym.Func.Text.Mark&LEAF == 0 {
 				// A very few functions that do not return to their caller