From: Keith Randall Date: Mon, 17 Sep 2018 21:46:07 +0000 (-0700) Subject: cmd/compile: don't do floating point optimization x+0 -> x X-Git-Tag: go1.12beta1~1057 X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=c6118af55864916c2c3b1bca8e216e627f232bf3;p=gostls13.git cmd/compile: don't do floating point optimization x+0 -> x That optimization is not valid if x == -0. The test is a bit tricky because 0 == -0. We distinguish 0 from -0 with 1/0 == inf, 1/-0 == -inf. This has been a bug since CL 24790 in Go 1.8. Probably doesn't warrant a backport. Fixes #27718 Note: the optimization x-0 -> x is actually valid. But it's probably best to take it out, so as to not confuse readers. Change-Id: I99f16a93b45f7406ec8053c2dc759a13eba035fa Reviewed-on: https://go-review.googlesource.com/135701 Reviewed-by: Cherry Zhang --- diff --git a/src/cmd/compile/internal/ssa/gen/generic.rules b/src/cmd/compile/internal/ssa/gen/generic.rules index e9677b15c7..2df29192a4 100644 --- a/src/cmd/compile/internal/ssa/gen/generic.rules +++ b/src/cmd/compile/internal/ssa/gen/generic.rules @@ -1329,9 +1329,6 @@ (Mul8 (Const8 [c]) (Mul8 (Const8 [d]) x)) -> (Mul8 (Const8 [int64(int8(c*d))]) x) // floating point optimizations -(Add(32|64)F x (Const(32|64)F [0])) -> x -(Sub(32|64)F x (Const(32|64)F [0])) -> x - (Mul(32|64)F x (Const(32|64)F [auxFrom64F(1)])) -> x (Mul32F x (Const32F [auxFrom32F(-1)])) -> (Neg32F x) (Mul64F x (Const64F [auxFrom64F(-1)])) -> (Neg64F x) diff --git a/src/cmd/compile/internal/ssa/rewritegeneric.go b/src/cmd/compile/internal/ssa/rewritegeneric.go index 612d57529e..422be65f9a 100644 --- a/src/cmd/compile/internal/ssa/rewritegeneric.go +++ b/src/cmd/compile/internal/ssa/rewritegeneric.go @@ -2445,42 +2445,6 @@ func rewriteValuegeneric_OpAdd32F_0(v *Value) bool { v.AuxInt = auxFrom32F(auxTo32F(c) + auxTo32F(d)) return true } - // match: (Add32F x (Const32F [0])) - // cond: - // result: x - for { - _ = v.Args[1] - x := v.Args[0] - v_1 := v.Args[1] - if v_1.Op != OpConst32F { - break - } - if v_1.AuxInt != 0 { - break - } - v.reset(OpCopy) - v.Type = x.Type - v.AddArg(x) - return true - } - // match: (Add32F (Const32F [0]) x) - // cond: - // result: x - for { - _ = v.Args[1] - v_0 := v.Args[0] - if v_0.Op != OpConst32F { - break - } - if v_0.AuxInt != 0 { - break - } - x := v.Args[1] - v.reset(OpCopy) - v.Type = x.Type - v.AddArg(x) - return true - } return false } func rewriteValuegeneric_OpAdd64_0(v *Value) bool { @@ -3490,42 +3454,6 @@ func rewriteValuegeneric_OpAdd64F_0(v *Value) bool { v.AuxInt = auxFrom64F(auxTo64F(c) + auxTo64F(d)) return true } - // match: (Add64F x (Const64F [0])) - // cond: - // result: x - for { - _ = v.Args[1] - x := v.Args[0] - v_1 := v.Args[1] - if v_1.Op != OpConst64F { - break - } - if v_1.AuxInt != 0 { - break - } - v.reset(OpCopy) - v.Type = x.Type - v.AddArg(x) - return true - } - // match: (Add64F (Const64F [0]) x) - // cond: - // result: x - for { - _ = v.Args[1] - v_0 := v.Args[0] - if v_0.Op != OpConst64F { - break - } - if v_0.AuxInt != 0 { - break - } - x := v.Args[1] - v.reset(OpCopy) - v.Type = x.Type - v.AddArg(x) - return true - } return false } func rewriteValuegeneric_OpAdd8_0(v *Value) bool { @@ -29841,24 +29769,6 @@ func rewriteValuegeneric_OpSub32F_0(v *Value) bool { v.AuxInt = auxFrom32F(auxTo32F(c) - auxTo32F(d)) return true } - // match: (Sub32F x (Const32F [0])) - // cond: - // result: x - for { - _ = v.Args[1] - x := v.Args[0] - v_1 := v.Args[1] - if v_1.Op != OpConst32F { - break - } - if v_1.AuxInt != 0 { - break - } - v.reset(OpCopy) - v.Type = x.Type - v.AddArg(x) - return true - } return false } func rewriteValuegeneric_OpSub64_0(v *Value) bool { @@ -30265,24 +30175,6 @@ func rewriteValuegeneric_OpSub64F_0(v *Value) bool { v.AuxInt = auxFrom64F(auxTo64F(c) - auxTo64F(d)) return true } - // match: (Sub64F x (Const64F [0])) - // cond: - // result: x - for { - _ = v.Args[1] - x := v.Args[0] - v_1 := v.Args[1] - if v_1.Op != OpConst64F { - break - } - if v_1.AuxInt != 0 { - break - } - v.reset(OpCopy) - v.Type = x.Type - v.AddArg(x) - return true - } return false } func rewriteValuegeneric_OpSub8_0(v *Value) bool { diff --git a/test/fixedbugs/issue27718.go b/test/fixedbugs/issue27718.go new file mode 100644 index 0000000000..f7794182f5 --- /dev/null +++ b/test/fixedbugs/issue27718.go @@ -0,0 +1,72 @@ +// run + +// Copyright 2018 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. + +// (-0)+0 should be 0, not -0. + +package main + +//go:noinline +func add64(x float64) float64 { + return x + 0 +} + +func testAdd64() { + var zero float64 + inf := 1.0 / zero + negZero := -1 / inf + if 1/add64(negZero) != inf { + panic("negZero+0 != posZero (64 bit)") + } +} + +//go:noinline +func sub64(x float64) float64 { + return x - 0 +} + +func testSub64() { + var zero float64 + inf := 1.0 / zero + negZero := -1 / inf + if 1/sub64(negZero) != -inf { + panic("negZero-0 != negZero (64 bit)") + } +} + +//go:noinline +func add32(x float32) float32 { + return x + 0 +} + +func testAdd32() { + var zero float32 + inf := 1.0 / zero + negZero := -1 / inf + if 1/add32(negZero) != inf { + panic("negZero+0 != posZero (32 bit)") + } +} + +//go:noinline +func sub32(x float32) float32 { + return x - 0 +} + +func testSub32() { + var zero float32 + inf := 1.0 / zero + negZero := -1 / inf + if 1/sub32(negZero) != -inf { + panic("negZero-0 != negZero (32 bit)") + } +} + +func main() { + testAdd64() + testSub64() + testAdd32() + testSub32() +}