We currently generate our own I/O signatures inside the DXIL parser, but
use the element counts from the DXBC container signatures to allocate
the input_params/output_params/patch_constant_params arrays. That
happens to work for well-behaved inputs, but it's asking for trouble.
We already check for error instructions when parsing swizzles, but if allocation
fails at codegen time we would like to avoid asserting when subsequently
constructing a swizzle.
Similar to d1c2ae3f0e, this is a bit too strict
and may prevent e.g. simultaneous use of float and float1 at codegen time.
However, in this case the inciting factor is that in the case of allocation
failure at codegen time, we would like to allow one or more arguments to have
error type.
The primary motivation here is to avoid needing to worry about instructions
potentially pointing to the preallocated error instruction in the case of
allocation failure.
This doesn't cover all passes, but none of the other passes make assumptions
about instruction sources.
This is because lower_nonconstant_array_loads() can potentially turn
nonconstant loads into constant loads, allowing copy-prop to turn these
loads into previous instructions, which might help other passes as well.
This patch lowers the number of required temps for the following ps_2_0
shader from 19 to 16:
int i;
float3x3 mats[4];
float4 main() : sv_target
{
return mul(mats[i], float3(1, 2, 3)).xyzz;
}
