cmd/compile: guard special register usage with GOEXPERIMENT=regabi

Previously, some special register uses are only guarded with ABI
wrapper generation (-abiwrap). This CL makes it also guarded with
the GOEXPERIMENT. This way we can enable only the wrapper
generation without fully the new ABI, for benchmarking purposes.

Change-Id: I90fc34afa1dc17c9c73e7b06e940e79e4c4bf7f6
Reviewed-on: https://go-review.googlesource.com/c/go/+/295289
Trust: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>

src/cmd/compile/internal/amd64/ssa.go

@@ -16,6 +16,7 @@ import (
 	"cmd/compile/internal/types"
 	"cmd/internal/obj"
 	"cmd/internal/obj/x86"
+	"cmd/internal/objabi"
 )
 
 // markMoves marks any MOVXconst ops that need to avoid clobbering flags.
@@ -845,7 +846,7 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 		if s.ABI != obj.ABIInternal {
 			v.Fatalf("MOVOstorezero can be only used in ABIInternal functions")
 		}
-		if !base.Flag.ABIWrap {
+		if !(objabi.Regabi_enabled == 1 && base.Flag.ABIWrap) {
 			// zeroing X15 manually if wrappers are not used
 			opregreg(s, x86.AXORPS, x86.REG_X15, x86.REG_X15)
 		}
@@ -945,7 +946,7 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 		if s.ABI != obj.ABIInternal {
 			v.Fatalf("MOVOconst can be only used in ABIInternal functions")
 		}
-		if !base.Flag.ABIWrap {
+		if !(objabi.Regabi_enabled == 1 && base.Flag.ABIWrap) {
 			// zeroing X15 manually if wrappers are not used
 			opregreg(s, x86.AXORPS, x86.REG_X15, x86.REG_X15)
 		}
@@ -1017,20 +1018,20 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 		// Closure pointer is DX.
 		ssagen.CheckLoweredGetClosurePtr(v)
 	case ssa.OpAMD64LoweredGetG:
-		if base.Flag.ABIWrap {
+		if objabi.Regabi_enabled == 1 && base.Flag.ABIWrap {
 			v.Fatalf("LoweredGetG should not appear in new ABI")
 		}
 		r := v.Reg()
 		getgFromTLS(s, r)
 	case ssa.OpAMD64CALLstatic:
-		if s.ABI == obj.ABI0 && v.Aux.(*ssa.AuxCall).Fn.ABI() == obj.ABIInternal {
+		if objabi.Regabi_enabled == 1 && s.ABI == obj.ABI0 && v.Aux.(*ssa.AuxCall).Fn.ABI() == obj.ABIInternal {
 			// zeroing X15 when entering ABIInternal from ABI0
 			opregreg(s, x86.AXORPS, x86.REG_X15, x86.REG_X15)
 			// set G register from TLS
 			getgFromTLS(s, x86.REG_R14)
 		}
 		s.Call(v)
-		if s.ABI == obj.ABIInternal && v.Aux.(*ssa.AuxCall).Fn.ABI() == obj.ABI0 {
+		if objabi.Regabi_enabled == 1 && s.ABI == obj.ABIInternal && v.Aux.(*ssa.AuxCall).Fn.ABI() == obj.ABI0 {
 			// zeroing X15 when entering ABIInternal from ABI0
 			opregreg(s, x86.AXORPS, x86.REG_X15, x86.REG_X15)
 			// set G register from TLS
@@ -1333,7 +1334,7 @@ func ssaGenBlock(s *ssagen.State, b, next *ssa.Block) {
 	case ssa.BlockRet:
 		s.Prog(obj.ARET)
 	case ssa.BlockRetJmp:
-		if s.ABI == obj.ABI0 && b.Aux.(*obj.LSym).ABI() == obj.ABIInternal {
+		if objabi.Regabi_enabled == 1 && s.ABI == obj.ABI0 && b.Aux.(*obj.LSym).ABI() == obj.ABIInternal {
 			// zeroing X15 when entering ABIInternal from ABI0
 			opregreg(s, x86.AXORPS, x86.REG_X15, x86.REG_X15)
 			// set G register from TLS

src/cmd/compile/internal/ssa/gen/AMD64.rules

@@ -459,7 +459,7 @@
 (IsInBounds idx len) => (SETB (CMPQ idx len))
 (IsSliceInBounds idx len) => (SETBE (CMPQ idx len))
 (NilCheck ...) => (LoweredNilCheck ...)
-(GetG mem) && !base.Flag.ABIWrap => (LoweredGetG mem) // only lower in old ABI. in new ABI we have a G register.
+(GetG mem) && !(objabi.Regabi_enabled == 1 && base.Flag.ABIWrap) => (LoweredGetG mem) // only lower in old ABI. in new ABI we have a G register.
 (GetClosurePtr ...) => (LoweredGetClosurePtr ...)
 (GetCallerPC ...) => (LoweredGetCallerPC ...)
 (GetCallerSP ...) => (LoweredGetCallerSP ...)