Currently, if an expression successfully parses according to the bison grammar,
but for one reason or another cannot generate a meaningful IR instruction, we
abort parsing with YYABORT. This includes, for example, an undefined variable or
function, invalid swizzle or field reference, or a constructor with a complex or
non-numeric data type.
Aborting parsing is unfortunate, however, because it means that any further
errors in the program cannot be caught by the programmer, increasing the number
of times they will need to fix errors and recompile.
The idea of this patch is that any such expression will instead generate an IR
node whose data type is of HLSL_CLASS_ERROR. Any further expression which would
consume an "error" typed instruction will instead immediately return an
expression of type "error" (probably the same one) instead of aborting or doing
any other type-checking.
Currently these "error" instructions should not pass the parsing stage, since
hlsl_compile_shader() will immediately notice that compilation has failed and
skip any optimization, lowering, or bytecode-writing.
A further direction to take this is to pre-allocate one "error" expression
immediately when creating the HLSL parser, and return that expression when we
fail to allocate an hlsl_ir_node of any type. This means we do not need to
handle allocation errors when constructing nodes, saving us quite a lot of error
handling (which is not only tedious but currently often broken, if nothing else
by virtue of neglecting cleanup of local variables).
I ran the compilation of ~1000 DXBC-TPF shaders randomly taken from
my collection and measured the performance using callgrind and the
kcachegrind "cycle count" estimation.
BEFORE:
* 1,846,641,596 cycles
* 1,845,635,336 cycles
* 1,841,335,225 cycles
AFTER:
* 1,764,035,136 cycles
* 1,767,948,767 cycles
* 1,773,927,734 cycles
So callgrind would estimate a 3.6% improvement at least.
The counterpoint is that the caller might get an allocation that
is potentially bigger than necessary. I would expect that allocation
to be rather short-lived anyway, so that's probably not a problem.
shader_signature_find_element_for_reg() is also used in the TPF parser,
where the program has not been validated yet, so it must not crash
on errors.
The I/O normaliser can instead assume that the shader is already
validated.
This fixes a crash with a shader used by The Falconeer. The bug is still
present, because the shader will be incorrectly rejected, but at least
the vkd3d-shader will fail gracefully.
