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?
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
