[dev.regabi] cmd/compile: refactor temp construction in walk

This CL adds a few new helper functions for constructing and
initializing temporary variables during walk.

Passes toolstash -cmp.

Change-Id: I54965d992cd8dfef7cb7dc92a17c88372e52a0d6
Reviewed-on: https://go-review.googlesource.com/c/go/+/284224
Trust: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>

5 files changed, 63 insertions, 45 deletions

diff --git a/src/cmd/compile/internal/walk/builtin.go b/src/cmd/compile/internal/walk/builtin.go
index 283c85629b..97f9de9c1d 100644
--- a/src/cmd/compile/internal/walk/builtin.go
+++ b/src/cmd/compile/internal/walk/builtin.go
@@ -277,10 +277,8 @@ func walkMakeMap(n *ir.MakeExpr, init *ir.Nodes) ir.Node {
 		// Allocate hmap on stack.
 
 		// var hv hmap
-		hv := typecheck.Temp(hmapType)
-		init.Append(typecheck.Stmt(ir.NewAssignStmt(base.Pos, hv, nil)))
 		// h = &hv
-		h = typecheck.NodAddr(hv)
+		h = stackTempAddr(init, hmapType)
 
 		// Allocate one bucket pointed to by hmap.buckets on stack if hint
 		// is not larger than BUCKETSIZE. In case hint is larger than
@@ -303,11 +301,8 @@ func walkMakeMap(n *ir.MakeExpr, init *ir.Nodes) ir.Node {
 			nif.Likely = true
 
 			// var bv bmap
-			bv := typecheck.Temp(reflectdata.MapBucketType(t))
-			nif.Body.Append(ir.NewAssignStmt(base.Pos, bv, nil))
-
 			// b = &bv
-			b := typecheck.NodAddr(bv)
+			b := stackTempAddr(&nif.Body, reflectdata.MapBucketType(t))
 
 			// h.buckets = b
 			bsym := hmapType.Field(5).Sym // hmap.buckets see reflect.go:hmap
@@ -509,9 +504,7 @@ func walkNew(n *ir.UnaryExpr, init *ir.Nodes) ir.Node {
 		if t.Size() >= ir.MaxImplicitStackVarSize {
 			base.Fatalf("large ONEW with EscNone: %v", n)
 		}
-		r := typecheck.Temp(t)
-		init.Append(typecheck.Stmt(ir.NewAssignStmt(base.Pos, r, nil))) // zero temp
-		return typecheck.Expr(typecheck.NodAddr(r))
+		return stackTempAddr(init, t)
 	}
 	types.CalcSize(t)
 	n.MarkNonNil()
diff --git a/src/cmd/compile/internal/walk/complit.go b/src/cmd/compile/internal/walk/complit.go
index f82ef69ca9..a7db453550 100644
--- a/src/cmd/compile/internal/walk/complit.go
+++ b/src/cmd/compile/internal/walk/complit.go
@@ -344,30 +344,14 @@ func slicelit(ctxt initContext, n *ir.CompLitExpr, var_ ir.Node, init *ir.Nodes)
 		if !types.Identical(t, x.Type()) {
 			panic("dotdotdot base type does not match order's assigned type")
 		}
-
-		if vstat == nil {
-			a = ir.NewAssignStmt(base.Pos, x, nil)
-			a = typecheck.Stmt(a)
-			init.Append(a) // zero new temp
-		} else {
-			// Declare that we're about to initialize all of x.
-			// (Which happens at the *vauto = vstat below.)
-			init.Append(ir.NewUnaryExpr(base.Pos, ir.OVARDEF, x))
-		}
-
-		a = typecheck.NodAddr(x)
+		a = initStackTemp(init, x, vstat != nil)
 	} else if n.Esc() == ir.EscNone {
-		a = typecheck.Temp(t)
 		if vstat == nil {
-			a = ir.NewAssignStmt(base.Pos, typecheck.Temp(t), nil)
-			a = typecheck.Stmt(a)
-			init.Append(a) // zero new temp
-			a = a.(*ir.AssignStmt).X
-		} else {
-			init.Append(ir.NewUnaryExpr(base.Pos, ir.OVARDEF, a))
+			// TODO(mdempsky): Remove this useless temporary.
+			// It's only needed to keep toolstash happy.
+			typecheck.Temp(t)
 		}
-
-		a = typecheck.NodAddr(a)
+		a = initStackTemp(init, typecheck.Temp(t), vstat != nil)
 	} else {
 		a = ir.NewUnaryExpr(base.Pos, ir.ONEW, ir.TypeNode(t))
 	}
@@ -550,9 +534,8 @@ func anylit(n ir.Node, var_ ir.Node, init *ir.Nodes) {
 
 		var r ir.Node
 		if n.Prealloc != nil {
-			// n.Right is stack temporary used as backing store.
-			appendWalkStmt(init, ir.NewAssignStmt(base.Pos, n.Prealloc, nil)) // zero backing store, just in case (#18410)
-			r = typecheck.NodAddr(n.Prealloc)
+			// n.Prealloc is stack temporary used as backing store.
+			r = initStackTemp(init, n.Prealloc, false)
 		} else {
 			r = ir.NewUnaryExpr(base.Pos, ir.ONEW, ir.TypeNode(n.X.Type()))
 			r.SetEsc(n.Esc())
diff --git a/src/cmd/compile/internal/walk/convert.go b/src/cmd/compile/internal/walk/convert.go
index b47bb917c3..d143c1084f 100644
--- a/src/cmd/compile/internal/walk/convert.go
+++ b/src/cmd/compile/internal/walk/convert.go
@@ -198,8 +198,7 @@ func walkBytesRunesToString(n *ir.ConvExpr, init *ir.Nodes) ir.Node {
 	a := typecheck.NodNil()
 	if n.Esc() == ir.EscNone {
 		// Create temporary buffer for string on stack.
-		t := types.NewArray(types.Types[types.TUINT8], tmpstringbufsize)
-		a = typecheck.NodAddr(typecheck.Temp(t))
+		a = stackBufAddr(tmpstringbufsize, types.Types[types.TUINT8])
 	}
 	if n.Op() == ir.ORUNES2STR {
 		// slicerunetostring(*[32]byte, []rune) string
@@ -229,8 +228,7 @@ func walkBytesToStringTemp(n *ir.ConvExpr, init *ir.Nodes) ir.Node {
 func walkRuneToString(n *ir.ConvExpr, init *ir.Nodes) ir.Node {
 	a := typecheck.NodNil()
 	if n.Esc() == ir.EscNone {
-		t := types.NewArray(types.Types[types.TUINT8], 4)
-		a = typecheck.NodAddr(typecheck.Temp(t))
+		a = stackBufAddr(4, types.Types[types.TUINT8])
 	}
 	// intstring(*[4]byte, rune)
 	return mkcall("intstring", n.Type(), init, a, typecheck.Conv(n.X, types.Types[types.TINT64]))
@@ -246,7 +244,7 @@ func walkStringToBytes(n *ir.ConvExpr, init *ir.Nodes) ir.Node {
 		t := types.NewArray(types.Types[types.TUINT8], int64(len(sc)))
 		var a ir.Node
 		if n.Esc() == ir.EscNone && len(sc) <= int(ir.MaxImplicitStackVarSize) {
-			a = typecheck.NodAddr(typecheck.Temp(t))
+			a = stackBufAddr(t.NumElem(), t.Elem())
 		} else {
 			types.CalcSize(t)
 			a = ir.NewUnaryExpr(base.Pos, ir.ONEW, nil)
@@ -273,8 +271,7 @@ func walkStringToBytes(n *ir.ConvExpr, init *ir.Nodes) ir.Node {
 	a := typecheck.NodNil()
 	if n.Esc() == ir.EscNone {
 		// Create temporary buffer for slice on stack.
-		t := types.NewArray(types.Types[types.TUINT8], tmpstringbufsize)
-		a = typecheck.NodAddr(typecheck.Temp(t))
+		a = stackBufAddr(tmpstringbufsize, types.Types[types.TUINT8])
 	}
 	// stringtoslicebyte(*32[byte], string) []byte
 	return mkcall("stringtoslicebyte", n.Type(), init, a, typecheck.Conv(s, types.Types[types.TSTRING]))
@@ -298,8 +295,7 @@ func walkStringToRunes(n *ir.ConvExpr, init *ir.Nodes) ir.Node {
 	a := typecheck.NodNil()
 	if n.Esc() == ir.EscNone {
 		// Create temporary buffer for slice on stack.
-		t := types.NewArray(types.Types[types.TINT32], tmpstringbufsize)
-		a = typecheck.NodAddr(typecheck.Temp(t))
+		a = stackBufAddr(tmpstringbufsize, types.Types[types.TINT32])
 	}
 	// stringtoslicerune(*[32]rune, string) []rune
 	return mkcall("stringtoslicerune", n.Type(), init, a, typecheck.Conv(n.X, types.Types[types.TSTRING]))
diff --git a/src/cmd/compile/internal/walk/expr.go b/src/cmd/compile/internal/walk/expr.go
index a1e8e63785..8a13f6a923 100644
--- a/src/cmd/compile/internal/walk/expr.go
+++ b/src/cmd/compile/internal/walk/expr.go
@@ -441,8 +441,7 @@ func walkAddString(n *ir.AddStringExpr, init *ir.Nodes) ir.Node {
 		// Don't allocate the buffer if the result won't fit.
 		if sz < tmpstringbufsize {
 			// Create temporary buffer for result string on stack.
-			t := types.NewArray(types.Types[types.TUINT8], tmpstringbufsize)
-			buf = typecheck.NodAddr(typecheck.Temp(t))
+			buf = stackBufAddr(tmpstringbufsize, types.Types[types.TUINT8])
 		}
 	}
 
diff --git a/src/cmd/compile/internal/walk/temp.go b/src/cmd/compile/internal/walk/temp.go
new file mode 100644
index 0000000000..901cb770f3
--- /dev/null
+++ b/src/cmd/compile/internal/walk/temp.go
@@ -0,0 +1,47 @@
+// Copyright 2021 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.
+
+package walk
+
+import (
+	"cmd/compile/internal/base"
+	"cmd/compile/internal/ir"
+	"cmd/compile/internal/typecheck"
+	"cmd/compile/internal/types"
+)
+
+// initStackTemp appends statements to init to initialize the given
+// temporary variable, and then returns the expression &tmp. If vardef
+// is true, then the variable is initialized with OVARDEF, and the
+// caller must ensure the variable is later assigned before use;
+// otherwise, it's zero initialized.
+//
+// TODO(mdempsky): Change callers to provide tmp's initial value,
+// rather than just vardef, to make this safer/easier to use.
+func initStackTemp(init *ir.Nodes, tmp *ir.Name, vardef bool) *ir.AddrExpr {
+	if vardef {
+		init.Append(ir.NewUnaryExpr(base.Pos, ir.OVARDEF, tmp))
+	} else {
+		appendWalkStmt(init, ir.NewAssignStmt(base.Pos, tmp, nil))
+	}
+	return typecheck.Expr(typecheck.NodAddr(tmp)).(*ir.AddrExpr)
+}
+
+// stackTempAddr returns the expression &tmp, where tmp is a newly
+// allocated temporary variable of the given type. Statements to
+// zero-initialize tmp are appended to init.
+func stackTempAddr(init *ir.Nodes, typ *types.Type) *ir.AddrExpr {
+	return initStackTemp(init, typecheck.Temp(typ), false)
+}
+
+// stackBufAddr returns thte expression &tmp, where tmp is a newly
+// allocated temporary variable of type [len]elem. This variable is
+// initialized, and elem must not contain pointers.
+func stackBufAddr(len int64, elem *types.Type) *ir.AddrExpr {
+	if elem.HasPointers() {
+		base.FatalfAt(base.Pos, "%v has pointers", elem)
+	}
+	tmp := typecheck.Temp(types.NewArray(elem, len))
+	return typecheck.Expr(typecheck.NodAddr(tmp)).(*ir.AddrExpr)
+}