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cmd/compile: diagnose constant division by complex zero
When casting an ideal to complex{64,128}, for example during the evaluation of var a = complex64(0) / 1e-50 we want the compiler to report a division-by-zero error if a divisor would be zero after the cast. We already do this for floats; for example var b = float32(0) / 1e-50 generates a 'division by zero' error at compile time (because float32(1e-50) is zero, and the cast is done before performing the division). There's no such check in the path for complex{64,128} expressions, and no cast is performed before the division in the evaluation of var a = complex64(0) / 1e-50 which compiles just fine. This patch changes the convlit1 function so that complex ideals components (real and imag) are correctly truncated to float{32,64} when doing an ideal -> complex{64, 128} cast. Fixes #11674 Change-Id: Ic5f8ee3c8cfe4c3bb0621481792c96511723d151 Reviewed-on: https://go-review.googlesource.com/37891 Run-TryBot: Alberto Donizetti <alb.donizetti@gmail.com> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Robert Griesemer <gri@golang.org>
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@ -160,6 +160,37 @@ func truncfltlit(oldv *Mpflt, t *types.Type) *Mpflt {
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return fv
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}
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// truncate Real and Imag parts of Mpcplx to 32-bit or 64-bit
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// precision, according to type; return truncated value. In case of
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// overflow, calls yyerror but does not truncate the input value.
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func trunccmplxlit(oldv *Mpcplx, t *types.Type) *Mpcplx {
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if t == nil {
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return oldv
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}
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if overflow(Val{oldv}, t) {
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// Avoid setting to Inf if there was an overflow. It's never
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// useful, and it'll cause spourious and confusing 'constant Inf
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// overflows float32' errors down the road.
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return oldv
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}
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cv := newMpcmplx()
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switch t.Etype {
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case TCOMPLEX64:
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cv.Real.SetFloat64(oldv.Real.Float32())
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cv.Imag.SetFloat64(oldv.Imag.Float32())
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case TCOMPLEX128:
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cv.Real.SetFloat64(oldv.Real.Float64())
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cv.Imag.SetFloat64(oldv.Imag.Float64())
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default:
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Fatalf("trunccplxlit: unexpected Etype %v", t.Etype)
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}
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return cv
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}
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// canReuseNode indicates whether it is known to be safe
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// to reuse a Node.
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type canReuseNode bool
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@ -361,7 +392,7 @@ func convlit1(n *Node, t *types.Type, explicit bool, reuse canReuseNode) *Node {
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fallthrough
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case CTCPLX:
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overflow(n.Val(), t)
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n.SetVal(Val{trunccmplxlit(n.Val().U.(*Mpcplx), t)})
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}
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} else if et == types.TSTRING && (ct == CTINT || ct == CTRUNE) && explicit {
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n.SetVal(tostr(n.Val()))
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@ -519,21 +550,25 @@ func doesoverflow(v Val, t *types.Type) bool {
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return false
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}
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func overflow(v Val, t *types.Type) {
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func overflow(v Val, t *types.Type) bool {
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// v has already been converted
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// to appropriate form for t.
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if t == nil || t.Etype == TIDEAL {
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return
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return false
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}
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// Only uintptrs may be converted to unsafe.Pointer, which cannot overflow.
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if t.Etype == TUNSAFEPTR {
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return
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return false
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}
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if doesoverflow(v, t) {
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yyerror("constant %v overflows %v", v, t)
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return true
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}
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return false
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}
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func tostr(v Val) Val {
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@ -37,6 +37,13 @@ func newMpflt() *Mpflt {
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return &a
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}
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func newMpcmplx() *Mpcplx {
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var a Mpcplx
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a.Real = *newMpflt()
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a.Imag = *newMpflt()
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return &a
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}
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func (a *Mpflt) SetInt(b *Mpint) {
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if b.checkOverflow(0) {
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// sign doesn't really matter but copy anyway
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63
src/cmd/compile/internal/gc/truncconst_test.go
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63
src/cmd/compile/internal/gc/truncconst_test.go
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@ -0,0 +1,63 @@
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// Copyright 2017 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package gc
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import "testing"
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var f52want float64 = 1.0 / (1 << 52)
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var f53want float64 = 1.0 / (1 << 53)
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func TestTruncFlt(t *testing.T) {
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const f52 = 1 + 1.0/(1<<52)
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const f53 = 1 + 1.0/(1<<53)
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if got := f52 - 1; got != f52want {
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t.Errorf("f52-1 = %g, want %g", got, f52want)
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}
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if got := float64(f52) - 1; got != f52want {
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t.Errorf("float64(f52)-1 = %g, want %g", got, f52want)
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}
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if got := f53 - 1; got != f53want {
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t.Errorf("f53-1 = %g, want %g", got, f53want)
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}
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if got := float64(f53) - 1; got != 0 {
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t.Errorf("float64(f53)-1 = %g, want 0", got)
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}
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}
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func TestTruncCmplx(t *testing.T) {
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const r52 = complex(1+1.0/(1<<52), 0)
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const r53 = complex(1+1.0/(1<<53), 0)
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if got := real(r52 - 1); got != f52want {
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t.Errorf("real(r52-1) = %g, want %g", got, f52want)
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}
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if got := real(complex128(r52) - 1); got != f52want {
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t.Errorf("real(complex128(r52)-1) = %g, want %g", got, f52want)
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}
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if got := real(r53 - 1); got != f53want {
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t.Errorf("real(r53-1) = %g, want %g", got, f53want)
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}
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if got := real(complex128(r53) - 1); got != 0 {
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t.Errorf("real(complex128(r53)-1) = %g, want 0", got)
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}
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const i52 = complex(0, 1+1.0/(1<<52))
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const i53 = complex(0, 1+1.0/(1<<53))
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if got := imag(i52 - 1i); got != f52want {
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t.Errorf("imag(i52-1i) = %g, want %g", got, f52want)
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}
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if got := imag(complex128(i52) - 1i); got != f52want {
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t.Errorf("imag(complex128(i52)-1i) = %g, want %g", got, f52want)
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}
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if got := imag(i53 - 1i); got != f53want {
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t.Errorf("imag(i53-1i) = %g, want %g", got, f53want)
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}
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if got := imag(complex128(i53) - 1i); got != 0 {
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t.Errorf("imag(complex128(i53)-1i) = %g, want 0", got)
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}
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}
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40
test/fixedbugs/issue11674.go
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40
test/fixedbugs/issue11674.go
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@ -0,0 +1,40 @@
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// errorcheck
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// Copyright 2017 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Issue 11674: cmd/compile: does not diagnose constant division by
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// zero
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package p
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const x complex64 = 0
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const y complex128 = 0
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var _ = x / 1e-20
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var _ = x / 1e-50 // ERROR "complex division by zero"
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var _ = x / 1e-1000 // ERROR "complex division by zero"
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var _ = x / 1e-20i
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var _ = x / 1e-50i // ERROR "complex division by zero"
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var _ = x / 1e-1000i // ERROR "complex division by zero"
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var _ = x / 1e-45 // smallest positive float32
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var _ = x / (1e-20 + 1e-20i)
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var _ = x / (1e-50 + 1e-20i)
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var _ = x / (1e-20 + 1e-50i)
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var _ = x / (1e-50 + 1e-50i) // ERROR "complex division by zero"
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var _ = x / (1e-1000 + 1e-1000i) // ERROR "complex division by zero"
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var _ = y / 1e-50
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var _ = y / 1e-1000 // ERROR "complex division by zero"
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var _ = y / 1e-50i
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var _ = y / 1e-1000i // ERROR "complex division by zero"
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var _ = y / 5e-324 // smallest positive float64
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var _ = y / (1e-50 + 1e-50)
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var _ = y / (1e-1000 + 1e-50i)
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var _ = y / (1e-50 + 1e-1000i)
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var _ = y / (1e-1000 + 1e-1000i) // ERROR "complex division by zero"
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