| Message ID | 20210923204253.903755-1-ppalka@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | real: fix encoding of negative IEEE double/quad values [PR98216] | expand |
On Thu, Sep 23, 2021 at 10:44 PM Patrick Palka via Gcc-patches <gcc-patches@gcc.gnu.org> wrote: > > In encode_ieee_double/quad, the assignment > > unsigned long VAL = r->sign << 31; > > is intended to set the 31st bit of VAL whenever the given REAL_CST is > negative. But on LP64 hosts it also unintentionally sets the upper 32 > bits of VAL due to the promotion of r->sign from unsigned:1 to int and > the subsequent sign extension of the shifted value from int to long. > > In the C++ frontend, this bug causes incorrect mangling of negative > double values due to the output of real_to_target during write_real_cst > unexpectedly having the upper 32 bits of each word set. (I'm not sure > if/how this bug manifests itself outside of the frontend..) > > This patch fixes this by avoiding the unwanted sign extension. Note > that r0-53976 fixed the same bug in encode_ieee_single long ago. > > Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for > trunk and perhaps the release branches? OK for trunk and branches. Thanks, Richard. > PR c++/98216 > PR c++/91292 > > gcc/ChangeLog: > > * real.c (encode_ieee_double): Avoid incorrect sign extension. > (encode_ieee_quad): Likewise. > > gcc/testsuite/ChangeLog: > > * g++.dg/cpp2a/nontype-float2.C: New test. > --- > gcc/real.c | 6 ++++-- > gcc/testsuite/g++.dg/cpp2a/nontype-float2.C | 13 +++++++++++++ > 2 files changed, 17 insertions(+), 2 deletions(-) > create mode 100644 gcc/testsuite/g++.dg/cpp2a/nontype-float2.C > > diff --git a/gcc/real.c b/gcc/real.c > index 555cf44c142..8c7a47a69e6 100644 > --- a/gcc/real.c > +++ b/gcc/real.c > @@ -3150,9 +3150,10 @@ encode_ieee_double (const struct real_format *fmt, long *buf, > const REAL_VALUE_TYPE *r) > { > unsigned long image_lo, image_hi, sig_lo, sig_hi, exp; > + unsigned long sign = r->sign; > bool denormal = (r->sig[SIGSZ-1] & SIG_MSB) == 0; > > - image_hi = r->sign << 31; > + image_hi = sign << 31; > image_lo = 0; > > if (HOST_BITS_PER_LONG == 64) > @@ -3938,10 +3939,11 @@ encode_ieee_quad (const struct real_format *fmt, long *buf, > const REAL_VALUE_TYPE *r) > { > unsigned long image3, image2, image1, image0, exp; > + unsigned long sign = r->sign; > bool denormal = (r->sig[SIGSZ-1] & SIG_MSB) == 0; > REAL_VALUE_TYPE u; > > - image3 = r->sign << 31; > + image3 = sign << 31; > image2 = 0; > image1 = 0; > image0 = 0; > diff --git a/gcc/testsuite/g++.dg/cpp2a/nontype-float2.C b/gcc/testsuite/g++.dg/cpp2a/nontype-float2.C > new file mode 100644 > index 00000000000..5db208a05d1 > --- /dev/null > +++ b/gcc/testsuite/g++.dg/cpp2a/nontype-float2.C > @@ -0,0 +1,13 @@ > +// PR c++/98216 > +// { dg-do compile { target c++20 } } > + > +template<auto> void f() { } > + > +template void f<-1.0f>(); > +template void f<-2.0f>(); > + > +template void f<-1.0>(); > +template void f<-2.0>(); > + > +template void f<-1.0L>(); > +template void f<-2.0L>(); > -- > 2.33.0.514.g99c99ed825 >
diff --git a/gcc/real.c b/gcc/real.c index 555cf44c142..8c7a47a69e6 100644 --- a/gcc/real.c +++ b/gcc/real.c @@ -3150,9 +3150,10 @@ encode_ieee_double (const struct real_format *fmt, long *buf, const REAL_VALUE_TYPE *r) { unsigned long image_lo, image_hi, sig_lo, sig_hi, exp; + unsigned long sign = r->sign; bool denormal = (r->sig[SIGSZ-1] & SIG_MSB) == 0; - image_hi = r->sign << 31; + image_hi = sign << 31; image_lo = 0; if (HOST_BITS_PER_LONG == 64) @@ -3938,10 +3939,11 @@ encode_ieee_quad (const struct real_format *fmt, long *buf, const REAL_VALUE_TYPE *r) { unsigned long image3, image2, image1, image0, exp; + unsigned long sign = r->sign; bool denormal = (r->sig[SIGSZ-1] & SIG_MSB) == 0; REAL_VALUE_TYPE u; - image3 = r->sign << 31; + image3 = sign << 31; image2 = 0; image1 = 0; image0 = 0; diff --git a/gcc/testsuite/g++.dg/cpp2a/nontype-float2.C b/gcc/testsuite/g++.dg/cpp2a/nontype-float2.C new file mode 100644 index 00000000000..5db208a05d1 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp2a/nontype-float2.C @@ -0,0 +1,13 @@ +// PR c++/98216 +// { dg-do compile { target c++20 } } + +template<auto> void f() { } + +template void f<-1.0f>(); +template void f<-2.0f>(); + +template void f<-1.0>(); +template void f<-2.0>(); + +template void f<-1.0L>(); +template void f<-2.0L>();