d: Fix comparing uninitialized memory in dstruct.d [PR116961]HEADtrunkmaster

Floating-point emulation in the D front-end is done via a type named
`struct longdouble`, which in GDC is a small interface around the
real_value type. Because the D code cannot include gcc/real.h directly,
a big enough buffer is used for the data instead.

On x86_64, this buffer is actually bigger than real_value itself, so
when a new longdouble object is created with

    longdouble r;
    real_from_string3 (&r.rv (), buffer, mode);
    return r;

there is uninitialized padding at the end of `r`.  This was never a
problem when D was implemented in C++ (until GCC 12) as comparing two
longdouble objects with `==' would be forwarded to the relevant
operator== overload that extracted the underlying real_value.

However when the front-end was translated to D, such conditions were
instead rewritten into identity comparisons

    return exp.toReal() is CTFloat.zero

The `is` operator gets lowered as a call to `memcmp() == 0', which is
where the read of uninitialized memory occurs, as seen by valgrind.

==26778== Conditional jump or move depends on uninitialised value(s)
==26778==    at 0x911F41: dmd.dstruct._isZeroInit(dmd.expression.Expression) (dstruct.d:635)
==26778==    by 0x9123BE: StructDeclaration::finalizeSize() (dstruct.d:373)
==26778==    by 0x86747C: dmd.aggregate.AggregateDeclaration.determineSize(ref const(dmd.location.Loc)) (aggregate.d:226)
[...]

To avoid accidentally reading uninitialized data, explicitly initialize
all `longdouble` variables with an empty constructor on C++ side of the
implementation before initializing underlying real_value type it holds.

	PR d/116961

gcc/d/ChangeLog:

	* d-codegen.cc (build_float_cst): Change new_value type from real_t to
	real_value.
	* d-ctfloat.cc (CTFloat::fabs): Default initialize the return value.
	(CTFloat::ldexp): Likewise.
	(CTFloat::parse): Likewise.
	* d-longdouble.cc (longdouble::add): Likewise.
	(longdouble::sub): Likewise.
	(longdouble::mul): Likewise.
	(longdouble::div): Likewise.
	(longdouble::mod): Likewise.
	(longdouble::neg): Likewise.
	* d-port.cc (Port::isFloat32LiteralOutOfRange): Likewise.
	(Port::isFloat64LiteralOutOfRange): Likewise.

gcc/testsuite/ChangeLog:

	* gdc.dg/pr116961.d: New test.

0 files changed, 0 insertions, 0 deletions