If the left-hand side of a logical operator is a constant that causes the
right-hand side to be short-circuited the right-hand side can be discarded
even if it is not constant.
In this case replace the expression by a constant.
E.g.
* `0 && expr` will be replaced by a constant 0.
* `1 || expr` will be replaced by a constant 1.
* `0 -> expr` will be replaced by a constant 1.
Note that it is not possible to replace the expression by a constant if
only the right-hand side is a constant, even when the value of the
expression is constant. The left side still has to be evaluated for side
effects.
E.g. it is known at elaboration that `a++ && 0` will yield 0, but the
increment on `a` has to be executed regardless.
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Section 11.4.7 of the SystemVerilog LRM states
```
The && and || operators shall use short circuit evaluation as follows:
- The first operand expression shall always be evaluated.
- For &&, if the first operand value is logically false then the second operand shall not be evaluated.
- For ||, if the first operand value is logically true then the second operand shall not be evaluated.
```
vvp currently evaluates both operands of a logical operator. This works
fine as long as the right-hand side does not have a side effect. But if it
has the result might be incorrect.
E.g. for `a && b++` `b` must not be incremented if `a` evaluates to false.
The Verilog LRM mentions that it is allowed to short circuit any expression
"if the final result of an expression can be determined early". But there
is no requirement to do so.
So the new and the old behavior are both correct implementations in
Verilog.
Use the new behavior in both Verilog and SystemVerilog mode to make sure
the behavior is consistent when an expression has side effects.
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
The code for generating the logical `and` and `or` operators is identical
except for the final opcode to combine the two results.
Consolidate this into a single function to reduce the code a bit.
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
If this assert fires, the "this" pointer we pass to it will be a
null pointer, so will cause a null pointer dereference. We've
tested it is not null earlier, so we don't need the assertion.
When using the latest mingw64 header files, rpcndr.h (which is indiretly
included by windows.h) defines a type named "byte" which collides with a
definition in cpp_type_traits.h (included indirectly by the STL). This is
only a problem if "using namespace std" is declared prior to including
windows.h.
For non-ANSI port declarations that have both a port declaration and
a corresponding variable declaration, the signed attribute may be
attached to either the port declaration or the variable declaration,
or both declarations.
This also ensures the same genvar cannot be used in two nested loops
(issue #533), because the implicit localparam with the same name
shadows the genvar declaration.
This requires us to make a copy of the typedefs map when adding it to
a NetScope object, because the pform data is deleted before we are
finished with it.
The IEEE standard specifies that the numbering of generate blocks
restarts at 1 in each new scope, and that the 'else' part of an 'if'
construct is part of the same constuct, so has the same number.
This eliminates some indeterminism in the error messages, which was
causing occasional failures in CI. We don't expect this list to be
very large, so the O(n) insertion time should not be a problem.
A module port list may contain unnamed entries, e.g.
module dut(a,);
When performing a wildcard connection, these entries should be skipped,
as there is no name to match.
The old implementation connected all inputs to the same vvp_net_t port,
on the basis that we don't care about the data values or what port they
arrived on. But if one or more of the inputs fans out to multiple nets,
the chains get tangled, which either results in connections being lost
or inappropriate connections being made, depending on the order that
the inputs are linked.
This could have been fixed by using a standard wide functor. But as we
don't care about the data values, that would be unnecessary overhead.
We just need separate vvp_net_t objects to handle the input connectivity
and can keep using a single shared functor.
This is needed for the waveform dumpers now that vpi_iterate(vpiModule, NULL)
has been ficed to only return modules.
This includes recognising vpiProgram and vpiInterface, although the compiler
and vvp currently incorrectly classify them as modules.
martinwhitaker
Lars-Peter Clausen
Michael Singer
Cary R
Martin Whitaker
Miodrag Milanovic