From d9b79e53bb40275d7974cbc14cc60fc1ce84f8f1 Mon Sep 17 00:00:00 2001 From: Junchen Li Date: Fri, 8 Jan 2021 10:20:34 +0800 Subject: [PATCH] cmd/compile: fix wrong complement for arm64 floating-point comparisons Consider the following example, func test(a, b float64, x uint64) uint64 { if a < b { x = 0 } return x } func main() { fmt.Println(test(1, math.NaN(), 123)) } The output is 0, but the expectation is 123. This is because the rewrite rule (CSEL [cc] (MOVDconst [0]) y flag) => (CSEL0 [arm64Negate(cc)] y flag) converts FCMP NaN, 1 CSEL MI, 0, 123, R0 // if 1 < NaN then R0 = 0 else R0 = 123 to FCMP NaN, 1 CSEL GE, 123, 0, R0 // if 1 >= NaN then R0 = 123 else R0 = 0 But both 1 < NaN and 1 >= NaN are false. So the output is 0, not 123. The root cause is arm64Negate not handle negation of floating comparison correctly. According to the ARM manual, the meaning of MI, GE, and PL are MI: Less than GE: Greater than or equal to PL: Greater than, equal to, or unordered Because NaN cannot be compared with other numbers, the result of such comparison is unordered. So when NaN is involved, unlike integer, the result of !(a < b) is not a >= b, it is a >= b || a is NaN || b is NaN. This is exactly what PL means. We add NotLessThanF to represent PL. Then the negation of LessThanF is NotLessThanF rather than GreaterEqualF. The same reason for the other floating comparison operations. Fixes #43619 Change-Id: Ia511b0027ad067436bace9fbfd261dbeaae01bcd Reviewed-on: https://go-review.googlesource.com/c/go/+/283572 Reviewed-by: Cherry Zhang Run-TryBot: Cherry Zhang TryBot-Result: Go Bot Trust: Keith Randall --- src/cmd/compile/internal/arm64/ssa.go | 20 +++- src/cmd/compile/internal/ssa/gen/ARM64Ops.go | 32 ++--- src/cmd/compile/internal/ssa/opGen.go | 40 +++++++ src/cmd/compile/internal/ssa/rewrite.go | 31 +++-- test/fixedbugs/issue43619.go | 119 +++++++++++++++++++ 5 files changed, 215 insertions(+), 27 deletions(-) create mode 100644 test/fixedbugs/issue43619.go diff --git a/src/cmd/compile/internal/arm64/ssa.go b/src/cmd/compile/internal/arm64/ssa.go index 22b28a9308..43588511ab 100644 --- a/src/cmd/compile/internal/arm64/ssa.go +++ b/src/cmd/compile/internal/arm64/ssa.go @@ -1054,7 +1054,11 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) { ssa.OpARM64LessThanF, ssa.OpARM64LessEqualF, ssa.OpARM64GreaterThanF, - ssa.OpARM64GreaterEqualF: + ssa.OpARM64GreaterEqualF, + ssa.OpARM64NotLessThanF, + ssa.OpARM64NotLessEqualF, + ssa.OpARM64NotGreaterThanF, + ssa.OpARM64NotGreaterEqualF: // generate boolean values using CSET p := s.Prog(arm64.ACSET) p.From.Type = obj.TYPE_REG // assembler encodes conditional bits in Reg @@ -1098,10 +1102,16 @@ var condBits = map[ssa.Op]int16{ ssa.OpARM64GreaterThanU: arm64.COND_HI, ssa.OpARM64GreaterEqual: arm64.COND_GE, ssa.OpARM64GreaterEqualU: arm64.COND_HS, - ssa.OpARM64LessThanF: arm64.COND_MI, - ssa.OpARM64LessEqualF: arm64.COND_LS, - ssa.OpARM64GreaterThanF: arm64.COND_GT, - ssa.OpARM64GreaterEqualF: arm64.COND_GE, + ssa.OpARM64LessThanF: arm64.COND_MI, // Less than + ssa.OpARM64LessEqualF: arm64.COND_LS, // Less than or equal to + ssa.OpARM64GreaterThanF: arm64.COND_GT, // Greater than + ssa.OpARM64GreaterEqualF: arm64.COND_GE, // Greater than or equal to + + // The following condition codes have unordered to handle comparisons related to NaN. + ssa.OpARM64NotLessThanF: arm64.COND_PL, // Greater than, equal to, or unordered + ssa.OpARM64NotLessEqualF: arm64.COND_HI, // Greater than or unordered + ssa.OpARM64NotGreaterThanF: arm64.COND_LE, // Less than, equal to or unordered + ssa.OpARM64NotGreaterEqualF: arm64.COND_LT, // Less than or unordered } var blockJump = map[ssa.BlockKind]struct { diff --git a/src/cmd/compile/internal/ssa/gen/ARM64Ops.go b/src/cmd/compile/internal/ssa/gen/ARM64Ops.go index 87db2b7c9d..b0bc9c78ff 100644 --- a/src/cmd/compile/internal/ssa/gen/ARM64Ops.go +++ b/src/cmd/compile/internal/ssa/gen/ARM64Ops.go @@ -478,20 +478,24 @@ func init() { // pseudo-ops {name: "LoweredNilCheck", argLength: 2, reg: regInfo{inputs: []regMask{gpg}}, nilCheck: true, faultOnNilArg0: true}, // panic if arg0 is nil. arg1=mem. - {name: "Equal", argLength: 1, reg: readflags}, // bool, true flags encode x==y false otherwise. - {name: "NotEqual", argLength: 1, reg: readflags}, // bool, true flags encode x!=y false otherwise. - {name: "LessThan", argLength: 1, reg: readflags}, // bool, true flags encode signed xy false otherwise. - {name: "GreaterEqual", argLength: 1, reg: readflags}, // bool, true flags encode signed x>=y false otherwise. - {name: "LessThanU", argLength: 1, reg: readflags}, // bool, true flags encode unsigned xy false otherwise. - {name: "GreaterEqualU", argLength: 1, reg: readflags}, // bool, true flags encode unsigned x>=y false otherwise. - {name: "LessThanF", argLength: 1, reg: readflags}, // bool, true flags encode floating-point xy false otherwise. - {name: "GreaterEqualF", argLength: 1, reg: readflags}, // bool, true flags encode floating-point x>=y false otherwise. + {name: "Equal", argLength: 1, reg: readflags}, // bool, true flags encode x==y false otherwise. + {name: "NotEqual", argLength: 1, reg: readflags}, // bool, true flags encode x!=y false otherwise. + {name: "LessThan", argLength: 1, reg: readflags}, // bool, true flags encode signed xy false otherwise. + {name: "GreaterEqual", argLength: 1, reg: readflags}, // bool, true flags encode signed x>=y false otherwise. + {name: "LessThanU", argLength: 1, reg: readflags}, // bool, true flags encode unsigned xy false otherwise. + {name: "GreaterEqualU", argLength: 1, reg: readflags}, // bool, true flags encode unsigned x>=y false otherwise. + {name: "LessThanF", argLength: 1, reg: readflags}, // bool, true flags encode floating-point xy false otherwise. + {name: "GreaterEqualF", argLength: 1, reg: readflags}, // bool, true flags encode floating-point x>=y false otherwise. + {name: "NotLessThanF", argLength: 1, reg: readflags}, // bool, true flags encode floating-point x>=y || x is unordered with y, false otherwise. + {name: "NotLessEqualF", argLength: 1, reg: readflags}, // bool, true flags encode floating-point x>y || x is unordered with y, false otherwise. + {name: "NotGreaterThanF", argLength: 1, reg: readflags}, // bool, true flags encode floating-point x<=y || x is unordered with y, false otherwise. + {name: "NotGreaterEqualF", argLength: 1, reg: readflags}, // bool, true flags encode floating-point x NotEqual or LessThan -> GreaterEqual +// for example !Equal -> NotEqual or !LessThan -> GreaterEqual // -// TODO: add floating-point conditions +// For floating point, it's more subtle because NaN is unordered. We do +// !LessThanF -> NotLessThanF, the latter takes care of NaNs. func arm64Negate(op Op) Op { switch op { case OpARM64LessThan: @@ -1000,13 +1001,21 @@ func arm64Negate(op Op) Op { case OpARM64NotEqual: return OpARM64Equal case OpARM64LessThanF: - return OpARM64GreaterEqualF - case OpARM64GreaterThanF: - return OpARM64LessEqualF + return OpARM64NotLessThanF + case OpARM64NotLessThanF: + return OpARM64LessThanF case OpARM64LessEqualF: + return OpARM64NotLessEqualF + case OpARM64NotLessEqualF: + return OpARM64LessEqualF + case OpARM64GreaterThanF: + return OpARM64NotGreaterThanF + case OpARM64NotGreaterThanF: return OpARM64GreaterThanF case OpARM64GreaterEqualF: - return OpARM64LessThanF + return OpARM64NotGreaterEqualF + case OpARM64NotGreaterEqualF: + return OpARM64GreaterEqualF default: panic("unreachable") } @@ -1017,8 +1026,6 @@ func arm64Negate(op Op) Op { // that the same result would be produced if the arguments // to the flag-generating instruction were reversed, e.g. // (InvertFlags (CMP x y)) -> (CMP y x) -// -// TODO: add floating-point conditions func arm64Invert(op Op) Op { switch op { case OpARM64LessThan: @@ -1047,6 +1054,14 @@ func arm64Invert(op Op) Op { return OpARM64GreaterEqualF case OpARM64GreaterEqualF: return OpARM64LessEqualF + case OpARM64NotLessThanF: + return OpARM64NotGreaterThanF + case OpARM64NotGreaterThanF: + return OpARM64NotLessThanF + case OpARM64NotLessEqualF: + return OpARM64NotGreaterEqualF + case OpARM64NotGreaterEqualF: + return OpARM64NotLessEqualF default: panic("unreachable") } diff --git a/test/fixedbugs/issue43619.go b/test/fixedbugs/issue43619.go new file mode 100644 index 0000000000..3e667851a4 --- /dev/null +++ b/test/fixedbugs/issue43619.go @@ -0,0 +1,119 @@ +// run + +// 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 main + +import ( + "fmt" + "math" +) + +//go:noinline +func fcmplt(a, b float64, x uint64) uint64 { + if a < b { + x = 0 + } + return x +} + +//go:noinline +func fcmple(a, b float64, x uint64) uint64 { + if a <= b { + x = 0 + } + return x +} + +//go:noinline +func fcmpgt(a, b float64, x uint64) uint64 { + if a > b { + x = 0 + } + return x +} + +//go:noinline +func fcmpge(a, b float64, x uint64) uint64 { + if a >= b { + x = 0 + } + return x +} + +//go:noinline +func fcmpeq(a, b float64, x uint64) uint64 { + if a == b { + x = 0 + } + return x +} + +//go:noinline +func fcmpne(a, b float64, x uint64) uint64 { + if a != b { + x = 0 + } + return x +} + +func main() { + type fn func(a, b float64, x uint64) uint64 + + type testCase struct { + f fn + a, b float64 + x, want uint64 + } + NaN := math.NaN() + for _, t := range []testCase{ + {fcmplt, 1.0, 1.0, 123, 123}, + {fcmple, 1.0, 1.0, 123, 0}, + {fcmpgt, 1.0, 1.0, 123, 123}, + {fcmpge, 1.0, 1.0, 123, 0}, + {fcmpeq, 1.0, 1.0, 123, 0}, + {fcmpne, 1.0, 1.0, 123, 123}, + + {fcmplt, 1.0, 2.0, 123, 0}, + {fcmple, 1.0, 2.0, 123, 0}, + {fcmpgt, 1.0, 2.0, 123, 123}, + {fcmpge, 1.0, 2.0, 123, 123}, + {fcmpeq, 1.0, 2.0, 123, 123}, + {fcmpne, 1.0, 2.0, 123, 0}, + + {fcmplt, 2.0, 1.0, 123, 123}, + {fcmple, 2.0, 1.0, 123, 123}, + {fcmpgt, 2.0, 1.0, 123, 0}, + {fcmpge, 2.0, 1.0, 123, 0}, + {fcmpeq, 2.0, 1.0, 123, 123}, + {fcmpne, 2.0, 1.0, 123, 0}, + + {fcmplt, 1.0, NaN, 123, 123}, + {fcmple, 1.0, NaN, 123, 123}, + {fcmpgt, 1.0, NaN, 123, 123}, + {fcmpge, 1.0, NaN, 123, 123}, + {fcmpeq, 1.0, NaN, 123, 123}, + {fcmpne, 1.0, NaN, 123, 0}, + + {fcmplt, NaN, 1.0, 123, 123}, + {fcmple, NaN, 1.0, 123, 123}, + {fcmpgt, NaN, 1.0, 123, 123}, + {fcmpge, NaN, 1.0, 123, 123}, + {fcmpeq, NaN, 1.0, 123, 123}, + {fcmpne, NaN, 1.0, 123, 0}, + + {fcmplt, NaN, NaN, 123, 123}, + {fcmple, NaN, NaN, 123, 123}, + {fcmpgt, NaN, NaN, 123, 123}, + {fcmpge, NaN, NaN, 123, 123}, + {fcmpeq, NaN, NaN, 123, 123}, + {fcmpne, NaN, NaN, 123, 0}, + } { + got := t.f(t.a, t.b, t.x) + if got != t.want { + panic(fmt.Sprintf("want %v, got %v", t.want, got)) + } + } +}