The F23 standard requires that a call to intrinsic module procedure
ieee_support_halting be foldable to a constant at compile time in some
contexts. See for example F23 Clause 10.1.11 [Specification expression]
list item (13), Clause 1.1.12 [Constant expression] list item (11), and
references to specification and constant expressions elsewhere, such as
constraints C1012, C853, and C704.
Some Arm processors allow a user to control processor behavior when an
arithmetic exception is signaled, and some Arm processors do not have
this capability. An Arm executable will run on either type of processor,
so it is effectively unknown at compile time whether or not this support
will be available at runtime. This is in conflict with the standard
requirement.
This patch addresses this conflict by implementing ieee_support_halting
calls on Arm processors to check if this capability is present at
runtime. A call to ieee_support_halting in a constant context, such as
in the specification part of a program unit, will generate a compile
time "cannot be computed as a constant value" error. The expectation is
that such calls are unlikely to appear in production code.
Code generation for other processors will continue to generate a compile
time constant result for ieee_support_halting calls.
The F23 standard requires that a call to intrinsic module procedure
ieee_support_halting be foldable to a constant at compile time in some
contexts. See for example F23 Clause 10.1.11 [Specification expression]
list item (13), Clause 1.1.12 [Constant expression] list item (11), and
references to specification and constant expressions elsewhere, such as
constraints C1012, C853, and C704.
Some Arm processors allow a user to control processor behavior when an
arithmetic exception is signaled, and some Arm processors do not have
this capability. An Arm executable will run on either type of processor,
so it is effectively unknown at compile time whether or not this support
will be available at runtime. This in conflict with the standard
requirement.
This patch addresses this conflict by implementing ieee_support_halting
calls on Arm processors to check if this capability is present at
runtime. A call to ieee_support_halting in a constant context, such as
in the specification part of a program unit, will generate a compile
time "cannot be computed as a constant value" error. The expectation is
that such calls are unlikely to appear in production code.
Code generation for other processors will continue to generate a compile
time constant result for ieee_support_halting calls.
According to the C99 standard, <fenv.h> may not define FE_INVALID and
the likes. Even if C++11 mandate them, musl and emscripten don't provide
them, so handle that case.
IEEE_ARITHMETIC intrinsic module procedures IEEE_NEXT_AFTER,
IEEE_NEXT_DOWN, and IEEE_NEXT_UP, and intrinsic NEAREST return larger or
smaller values adjacent to their primary REAL argument. The four
procedures vary in how the direction is chosen, in how special cases are
treated, and in what exceptions are generated. Implement the three
IEEE_ARITHMETIC procedures. Update the NEAREST implementation to support
all six REAL kinds 2,3,4,8,10,16, and fix several bugs.
IEEE_NEXT_AFTER(X,Y) returns a NaN when Y is a NaN as that seems to be
the universal choice of other compilers.
Change the front end compile time implementation of these procedures to
return normal (HUGE) values for infinities when applicable, rather than
always returning the input infinity.
Even after 13e2200fa426faffb62bdaf8b2f1f5699eee1511 (Solaris lacks
`femode_t`, too), the Solaris `flang` build is still broken:
```
/vol/llvm/src/llvm-project/local/flang/runtime/exceptions.cpp:87:5: error: static assertion failed due to requirement 'sizeof(fenv_t) <= sizeof(int) * 8': increase ieee_status_type size
87 | sizeof(fenv_t) <= sizeof(int) * _FORTRAN_RUNTIME_IEEE_FENV_T_EXTENT, | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/vol/llvm/src/llvm-project/local/flang/runtime/exceptions.cpp:87:20: note: expression evaluates to '200 <= 32'
87 | sizeof(fenv_t) <= sizeof(int) * _FORTRAN_RUNTIME_IEEE_FENV_T_EXTENT, | ~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
```
This patch fixes this by removing the assertion.
Tested on `amd64-pc-solaris2.11` and `sparcv9-sun-solaris2.11`.
AIX does not have `femode_t` in `<cfenv>` header, removing the assert to
fix build failures
---------
Co-authored-by: Mark Danial <mark.danial@ibm.com>
