cmd/compile: remove stale register use array

The reg[] array in .../gc is where truth lies.  The copy in .../ARCH
is incorrect as it is mostly not updated to reflect regalloc decisions.

This bug was introduced in the rewrite
https://go-review.googlesource.com/#/c/7853/.  The new reg[] array was
introduced in .../gc but not all of the uses were removed in the
.../ARCH directories.

Fixes #12133

Change-Id: I6364fc403cdab92d802d17f2913ba1607734037c
Reviewed-on: https://go-review.googlesource.com/13630Reviewed-by: Russ Cox <rsc@golang.org>

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

@@ -306,7 +306,7 @@ func dodiv(op int, nl *gc.Node, nr *gc.Node, res *gc.Node) {
  * known to be dead.
  */
 func savex(dr int, x *gc.Node, oldx *gc.Node, res *gc.Node, t *gc.Type) {
-	r := reg[dr]
+	r := uint8(gc.GetReg(dr))
 
 	// save current ax and dx if they are live
 	// and not the destination
@@ -319,14 +319,14 @@ func savex(dr int, x *gc.Node, oldx *gc.Node, res *gc.Node, t *gc.Type) {
 		gmove(x, oldx)
 		x.Type = t
 		oldx.Etype = r // squirrel away old r value
-		reg[dr] = 1
+		gc.SetReg(dr, 1)
 	}
 }
 
 func restx(x *gc.Node, oldx *gc.Node) {
 	if oldx.Op != 0 {
 		x.Type = gc.Types[gc.TINT64]
-		reg[x.Reg] = oldx.Etype
+		gc.SetReg(int(x.Reg), int(oldx.Etype))
 		gmove(oldx, x)
 		gc.Regfree(oldx)
 	}
@@ -411,7 +411,7 @@ func cgen_shift(op int, bounded bool, nl *gc.Node, nr *gc.Node, res *gc.Node) {
 		nr = &n5
 	}
 
-	rcx := int(reg[x86.REG_CX])
+	rcx := gc.GetReg(x86.REG_CX)
 	var n1 gc.Node
 	gc.Nodreg(&n1, gc.Types[gc.TUINT32], x86.REG_CX)
 

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

@@ -40,8 +40,6 @@ const (
 	NREGVAR = 32
 )
 
-var reg [x86.MAXREG]uint8
-
 var regname = []string{
 	".AX",
 	".CX",

src/cmd/compile/internal/arm64/ggen.go

@@ -418,7 +418,7 @@ func clearfat(nl *gc.Node) {
 	c := uint64(w % 8) // bytes
 	q := uint64(w / 8) // dwords
 
-	if reg[arm64.REGRT1-arm64.REG_R0] > 0 {
+	if gc.GetReg(arm64.REGRT1) > 0 {
 		gc.Fatal("R%d in use during clearfat", arm64.REGRT1-arm64.REG_R0)
 	}
 
@@ -426,7 +426,7 @@ func clearfat(nl *gc.Node) {
 	gc.Nodreg(&r0, gc.Types[gc.TUINT64], arm64.REGZERO)
 	var dst gc.Node
 	gc.Nodreg(&dst, gc.Types[gc.Tptr], arm64.REGRT1)
-	reg[arm64.REGRT1-arm64.REG_R0]++
+	gc.SetReg(arm64.REGRT1, gc.GetReg(arm64.REGRT1)+1)
 	gc.Agen(nl, &dst)
 
 	var boff uint64
@@ -485,7 +485,7 @@ func clearfat(nl *gc.Node) {
 		p.To.Offset = int64(t + boff)
 	}
 
-	reg[arm64.REGRT1-arm64.REG_R0]--
+	gc.SetReg(arm64.REGRT1, gc.GetReg(arm64.REGRT1)-1)
 }
 
 // Called after regopt and peep have run.

src/cmd/compile/internal/arm64/reg.go

@@ -39,8 +39,6 @@ const (
 	NREGVAR = 64 /* 32 general + 32 floating */
 )
 
-var reg [arm64.NREG + arm64.NFREG]uint8
-
 var regname = []string{
 	".R0",
 	".R1",

src/cmd/compile/internal/gc/gsubr.go

@@ -602,6 +602,13 @@ func unpatch(p *obj.Prog) *obj.Prog {
 var reg [100]int       // count of references to reg
 var regstk [100][]byte // allocation sites, when -v is given
 
+func GetReg(r int) int {
+	return reg[r-Thearch.REGMIN]
+}
+func SetReg(r, v int) {
+	reg[r-Thearch.REGMIN] = v
+}
+
 func ginit() {
 	for r := range reg {
 		reg[r] = 1

src/cmd/compile/internal/x86/ggen.go

@@ -319,7 +319,7 @@ func dodiv(op int, nl *gc.Node, nr *gc.Node, res *gc.Node, ax *gc.Node, dx *gc.N
 }
 
 func savex(dr int, x *gc.Node, oldx *gc.Node, res *gc.Node, t *gc.Type) {
-	r := int(reg[dr])
+	r := gc.GetReg(dr)
 	gc.Nodreg(x, gc.Types[gc.TINT32], dr)
 
 	// save current ax and dx if they are live
@@ -408,7 +408,7 @@ func cgen_shift(op int, bounded bool, nl *gc.Node, nr *gc.Node, res *gc.Node) {
 	var oldcx gc.Node
 	var cx gc.Node
 	gc.Nodreg(&cx, gc.Types[gc.TUINT32], x86.REG_CX)
-	if reg[x86.REG_CX] > 1 && !gc.Samereg(&cx, res) {
+	if gc.GetReg(x86.REG_CX) > 1 && !gc.Samereg(&cx, res) {
 		gc.Tempname(&oldcx, gc.Types[gc.TUINT32])
 		gmove(&cx, &oldcx)
 	}

src/cmd/compile/internal/x86/reg.go

@@ -37,8 +37,6 @@ const (
 	NREGVAR = 16 /* 8 integer + 8 floating */
 )
 
-var reg [x86.MAXREG]uint8
-
 var regname = []string{
 	".ax",
 	".cx",

test/fixedbugs/issue12133.go

+// run
+
+// Copyright 2015 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Issue 12133.  The CX register was getting clobbered
+// because we did not keep track of its allocation correctly.
+
+package main
+
+import "fmt"
+
+func main() {
+	want := uint(48)
+	got := f1(48)
+	if got != want {
+		fmt.Println("got", got, ", wanted", want)
+		panic("bad")
+	}
+}
+func f1(v1 uint) uint {
+	switch {
+	} // prevent inlining
+	return v1 >> ((1 >> v1) + (1 >> v1))
+}