diff options
Diffstat (limited to 'src/cmd/compile/internal/deadcode/deadcode.go')
-rw-r--r-- | src/cmd/compile/internal/deadcode/deadcode.go | 150 |
1 files changed, 150 insertions, 0 deletions
diff --git a/src/cmd/compile/internal/deadcode/deadcode.go b/src/cmd/compile/internal/deadcode/deadcode.go new file mode 100644 index 0000000000..5453cfe396 --- /dev/null +++ b/src/cmd/compile/internal/deadcode/deadcode.go @@ -0,0 +1,150 @@ +// Copyright 2009 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 deadcode + +import ( + "go/constant" + + "cmd/compile/internal/base" + "cmd/compile/internal/ir" +) + +func Func(fn *ir.Func) { + stmts(&fn.Body) + + if len(fn.Body) == 0 { + return + } + + for _, n := range fn.Body { + if len(n.Init()) > 0 { + return + } + switch n.Op() { + case ir.OIF: + n := n.(*ir.IfStmt) + if !ir.IsConst(n.Cond, constant.Bool) || len(n.Body) > 0 || len(n.Else) > 0 { + return + } + case ir.OFOR: + n := n.(*ir.ForStmt) + if !ir.IsConst(n.Cond, constant.Bool) || ir.BoolVal(n.Cond) { + return + } + default: + return + } + } + + fn.Body.Set([]ir.Node{ir.NewBlockStmt(base.Pos, nil)}) +} + +func stmts(nn *ir.Nodes) { + var lastLabel = -1 + for i, n := range *nn { + if n != nil && n.Op() == ir.OLABEL { + lastLabel = i + } + } + for i, n := range *nn { + // Cut is set to true when all nodes after i'th position + // should be removed. + // In other words, it marks whole slice "tail" as dead. + cut := false + if n == nil { + continue + } + if n.Op() == ir.OIF { + n := n.(*ir.IfStmt) + n.Cond = expr(n.Cond) + if ir.IsConst(n.Cond, constant.Bool) { + var body ir.Nodes + if ir.BoolVal(n.Cond) { + n.Else = ir.Nodes{} + body = n.Body + } else { + n.Body = ir.Nodes{} + body = n.Else + } + // If "then" or "else" branch ends with panic or return statement, + // it is safe to remove all statements after this node. + // isterminating is not used to avoid goto-related complications. + // We must be careful not to deadcode-remove labels, as they + // might be the target of a goto. See issue 28616. + if body := body; len(body) != 0 { + switch body[(len(body) - 1)].Op() { + case ir.ORETURN, ir.ORETJMP, ir.OPANIC: + if i > lastLabel { + cut = true + } + } + } + } + } + + stmts(n.PtrInit()) + switch n.Op() { + case ir.OBLOCK: + n := n.(*ir.BlockStmt) + stmts(&n.List) + case ir.OFOR: + n := n.(*ir.ForStmt) + stmts(&n.Body) + case ir.OIF: + n := n.(*ir.IfStmt) + stmts(&n.Body) + stmts(&n.Else) + case ir.ORANGE: + n := n.(*ir.RangeStmt) + stmts(&n.Body) + case ir.OSELECT: + n := n.(*ir.SelectStmt) + for _, cas := range n.Cases { + stmts(&cas.Body) + } + case ir.OSWITCH: + n := n.(*ir.SwitchStmt) + for _, cas := range n.Cases { + stmts(&cas.Body) + } + } + + if cut { + nn.Set((*nn)[:i+1]) + break + } + } +} + +func expr(n ir.Node) ir.Node { + // Perform dead-code elimination on short-circuited boolean + // expressions involving constants with the intent of + // producing a constant 'if' condition. + switch n.Op() { + case ir.OANDAND: + n := n.(*ir.LogicalExpr) + n.X = expr(n.X) + n.Y = expr(n.Y) + if ir.IsConst(n.X, constant.Bool) { + if ir.BoolVal(n.X) { + return n.Y // true && x => x + } else { + return n.X // false && x => false + } + } + case ir.OOROR: + n := n.(*ir.LogicalExpr) + n.X = expr(n.X) + n.Y = expr(n.Y) + if ir.IsConst(n.X, constant.Bool) { + if ir.BoolVal(n.X) { + return n.X // true || x => true + } else { + return n.Y // false || x => x + } + } + } + return n +} |