We're already using functions not made available through either
metal_common or metal_texture. This doesn't seem to be an issue for the
Metal shader runner, possibly because the "online" compiler includes the
required headers by default. In any case, including metal_stdlib should
make all of MSLib available.
MSL doesn't seem to have any special handling for undefined values,
differently from SPIR-V. Thus we just emit zeros.
UNDEF registers are sometimes created by the DXIL parser,
for example in sm6_parser_emit_composite_construct().
For an if block
if (cond)
{
<then_block>
}
else
{
<else_block>
}
We flatten it by first replacing any store instruction `v[[k]] = x`
in the then_block with the following:
1: load(v[[k]])
2: cond ? x : @1
3: v[[k]] = @2
Similarly, we replace any store instruction `v[[k]] = x` in the
else_block with the following:
1: load(v[[k]])
2: cond ? @1 : x
3: v[[k]] = @2
Then we can concatenate <then_block> and <else_block> together and
get rid of the if block.
The input DXIL can sometimes contain constant arrays not referenced by the
resulting vsir program. It doesn't hurt much to generate ICBs for those
anyway, but it's a little pointless.
