diff options
| -rw-r--r-- | src/cmd/compile/internal/gc/walk.go | 66 | ||||
| -rw-r--r-- | test/prove.go | 2 |
2 files changed, 51 insertions, 17 deletions
diff --git a/src/cmd/compile/internal/gc/walk.go b/src/cmd/compile/internal/gc/walk.go index e53fd7ac97..2c873b8163 100644 --- a/src/cmd/compile/internal/gc/walk.go +++ b/src/cmd/compile/internal/gc/walk.go @@ -1371,20 +1371,7 @@ opswitch: n = callnew(n.Type.Elem()) } - // If one argument to the comparison is an empty string, - // comparing the lengths instead will yield the same result - // without the function call. case OCMPSTR: - if (Isconst(n.Left, CTSTR) && len(n.Left.Val().U.(string)) == 0) || (Isconst(n.Right, CTSTR) && len(n.Right.Val().U.(string)) == 0) { - // TODO(marvin): Fix Node.EType type union. - r := Nod(Op(n.Etype), Nod(OLEN, n.Left, nil), Nod(OLEN, n.Right, nil)) - r = typecheck(r, Erv) - r = walkexpr(r, init) - r.Type = n.Type - n = r - break - } - // s + "badgerbadgerbadger" == "badgerbadgerbadger" if (Op(n.Etype) == OEQ || Op(n.Etype) == ONE) && Isconst(n.Right, CTSTR) && n.Left.Op == OADDSTR && n.Left.List.Len() == 2 && Isconst(n.Left.List.Second(), CTSTR) && strlit(n.Right) == strlit(n.Left.List.Second()) { // TODO(marvin): Fix Node.EType type union. @@ -1396,12 +1383,61 @@ opswitch: break } + // Rewrite comparisons to short constant strings as length+byte-wise comparisons. + var cs, ncs *Node // const string, non-const string + switch { + case Isconst(n.Left, CTSTR) && Isconst(n.Right, CTSTR): + // ignore; will be constant evaluated + case Isconst(n.Left, CTSTR): + cs = n.Left + ncs = n.Right + case Isconst(n.Right, CTSTR): + cs = n.Right + ncs = n.Left + } + if cs != nil { + cmp := Op(n.Etype) + // maxRewriteLen was chosen empirically. + // It is the value that minimizes cmd/go file size + // across most architectures. + // See the commit description for CL 26758 for details. + maxRewriteLen := 6 + var and Op + switch cmp { + case OEQ: + and = OANDAND + case ONE: + and = OOROR + default: + // Don't do byte-wise comparisons for <, <=, etc. + // They're fairly complicated. + // Length-only checks are ok, though. + maxRewriteLen = 0 + } + if s := cs.Val().U.(string); len(s) <= maxRewriteLen { + if len(s) > 0 { + ncs = safeexpr(ncs, init) + } + // TODO(marvin): Fix Node.EType type union. + r := Nod(cmp, Nod(OLEN, ncs, nil), Nodintconst(int64(len(s)))) + for i := 0; i < len(s); i++ { + cb := Nodintconst(int64(s[i])) + ncb := Nod(OINDEX, ncs, Nodintconst(int64(i))) + r = Nod(and, r, Nod(cmp, ncb, cb)) + } + r = typecheck(r, Erv) + r = walkexpr(r, init) + r.Type = n.Type + n = r + break + } + } + var r *Node // TODO(marvin): Fix Node.EType type union. if Op(n.Etype) == OEQ || Op(n.Etype) == ONE { // prepare for rewrite below n.Left = cheapexpr(n.Left, init) - n.Right = cheapexpr(n.Right, init) r = mkcall("eqstring", Types[TBOOL], init, conv(n.Left, Types[TSTRING]), conv(n.Right, Types[TSTRING])) @@ -1415,7 +1451,6 @@ opswitch: } else { // len(left) != len(right) || !eqstring(left, right) r = Nod(ONOT, r, nil) - r = Nod(OOROR, Nod(ONE, Nod(OLEN, n.Left, nil), Nod(OLEN, n.Right, nil)), r) } @@ -1424,7 +1459,6 @@ opswitch: } else { // sys_cmpstring(s1, s2) :: 0 r = mkcall("cmpstring", Types[TINT], init, conv(n.Left, Types[TSTRING]), conv(n.Right, Types[TSTRING])) - // TODO(marvin): Fix Node.EType type union. r = Nod(Op(n.Etype), r, nodintconst(0)) } diff --git a/test/prove.go b/test/prove.go index 8bcc9ae614..65eed745cb 100644 --- a/test/prove.go +++ b/test/prove.go @@ -250,7 +250,7 @@ func f9(a, b bool) int { func f10(a string) int { n := len(a) - if a[:n>>1] == "aaa" { + if a[:n>>1] == "aaaaaaaaaaaaaa" { return 0 } return 1 |