From e26499153e938b21850a7b6b33f27bb3d98e01cd Mon Sep 17 00:00:00 2001 From: Josh Bleecher Snyder Date: Sun, 5 Jun 2016 17:28:28 -0700 Subject: [PATCH] cmd/compile: use a map to track const switch cases This is simpler than the sorting technique. It also allows us to simplify or eliminate some of the sorting decisions. Most important, sorting will not work when case clauses represent ranges of integers: There is no correct sort order that allows overlap detection by comparing neighbors. Using a map allows of a cheap, simple approach to ranges, namely to insert every int in the map. The equivalent approach for sorting means juggling temporary Nodes for every int, which is a lot more expensive. Change-Id: I84df3cb805992a1b04d14e0e4b2334f943e0ce05 Reviewed-on: https://go-review.googlesource.com/26766 Run-TryBot: Josh Bleecher Snyder Reviewed-by: Matthew Dempsky --- src/cmd/compile/internal/gc/const.go | 21 +++++++++ src/cmd/compile/internal/gc/swt.go | 64 ++++++++++++++++++++++------ test/switch5.go | 11 +++++ 3 files changed, 82 insertions(+), 14 deletions(-) diff --git a/src/cmd/compile/internal/gc/const.go b/src/cmd/compile/internal/gc/const.go index 4b4cffdc06..078e991758 100644 --- a/src/cmd/compile/internal/gc/const.go +++ b/src/cmd/compile/internal/gc/const.go @@ -89,6 +89,27 @@ func eqval(a, b Val) bool { } } +// Interface returns the constant value stored in v as an interface{}. +// It returns int64s for ints and runes, float64s for floats, +// complex128s for complex values, and nil for constant nils. +func (v Val) Interface() interface{} { + switch x := v.U.(type) { + default: + Fatalf("unexpected Interface for %T", v.U) + panic("not reached") + case *NilVal: + return nil + case bool, string: + return x + case *Mpint: + return x.Int64() + case *Mpflt: + return x.Float64() + case *Mpcplx: + return complex(x.Real.Float64(), x.Imag.Float64()) + } +} + type NilVal struct{} // IntLiteral returns the Node's literal value as an integer. diff --git a/src/cmd/compile/internal/gc/swt.go b/src/cmd/compile/internal/gc/swt.go index 5c756dfa81..c053099681 100644 --- a/src/cmd/compile/internal/gc/swt.go +++ b/src/cmd/compile/internal/gc/swt.go @@ -517,17 +517,59 @@ func (s *exprSwitch) checkDupCases(cc []caseClause) { if len(cc) < 2 { return } - sort.Sort(caseClauseByExpr(cc)) - for i, c1 := range cc[:len(cc)-1] { - c2 := cc[i+1] - if exprcmp(c1, c2) != 0 { + // The common case is that s's expression is not an interface. + // In that case, all constant clauses have the same type, + // so checking for duplicates can be done solely by value. + if !s.exprname.Type.IsInterface() { + seen := make(map[interface{}]*Node) + for _, c := range cc { + // Can't check for duplicates that aren't constants, per the spec. Issue 15896. + // Don't check for duplicate bools. Although the spec allows it, + // (1) the compiler hasn't checked it in the past, so compatibility mandates it, and + // (2) it would disallow useful things like + // case GOARCH == "arm" && GOARM == "5": + // case GOARCH == "arm": + // which would both evaluate to false for non-ARM compiles. + if ct := consttype(c.node.Left); ct < 0 || ct == CTBOOL { + continue + } + val := c.node.Left.Val().Interface() + prev, dup := seen[val] + if !dup { + seen[val] = c.node + continue + } + setlineno(c.node) + Yyerror("duplicate case %v in switch\n\tprevious case at %v", prev.Left, prev.Line()) + } + return + } + // s's expression is an interface. This is fairly rare, so keep this simple. + // Duplicates are only duplicates if they have the same type and the same value. + type typeVal struct { + typ string + val interface{} + } + seen := make(map[typeVal]*Node) + for _, c := range cc { + if ct := consttype(c.node.Left); ct < 0 || ct == CTBOOL { + continue + } + n := c.node.Left + tv := typeVal{ + // Tconv here serves to completely describe the type. + // See the comments in func typehash. + typ: Tconv(n.Type, FmtLeft|FmtUnsigned), + val: n.Val().Interface(), + } + prev, dup := seen[tv] + if !dup { + seen[tv] = c.node continue } - setlineno(c2.node) - Yyerror("duplicate case %v in switch\n\tprevious case at %v", c1.node.Left, c1.node.Line()) + setlineno(c.node) + Yyerror("duplicate case %v in switch\n\tprevious case at %v", prev.Left, prev.Line()) } - // put list back in processing order - sort.Sort(caseClauseByOrd(cc)) } // walk generates an AST that implements sw, @@ -736,12 +778,6 @@ func (s *typeSwitch) walkCases(cc []caseClause) *Node { return a } -type caseClauseByOrd []caseClause - -func (x caseClauseByOrd) Len() int { return len(x) } -func (x caseClauseByOrd) Swap(i, j int) { x[i], x[j] = x[j], x[i] } -func (x caseClauseByOrd) Less(i, j int) bool { return x[i].ordinal < x[j].ordinal } - type caseClauseByExpr []caseClause func (x caseClauseByExpr) Len() int { return len(x) } diff --git a/test/switch5.go b/test/switch5.go index bb0f5e33ad..54a11b5c9a 100644 --- a/test/switch5.go +++ b/test/switch5.go @@ -79,3 +79,14 @@ func f5(a [1]int) { case [1]int{0}: // OK -- see issue 15896 } } + +// Ensure duplicate const bool clauses are accepted. +func f6() int { + switch { + case 0 == 0: + return 0 + case 1 == 1: // Intentionally OK, even though a duplicate of the above const true + return 1 + } + return 2 +} -- 2.48.1