Speculate that we can modify the SSA value in-place. As long as it is
not used after the modify, this is fine.
Also need to make sure we don't attempt to RMW something that is
impossible to modify.
GLSL and RelaxedPrecision are quite different in what they affect.
RelaxedPrecision affects operations, while this is merely implied in
GLSL based on inputs.
This leads to situations where we have to promote mediump inputs to
highp, and the simplest approach is to force highp temporaries for
inputs which are consumed in a highp context. For completeness, we also
demote RelaxedPrecision inputs to mediump variables.
PHI is handled by copying the PHI into a temporary.
We have to be very careful with hoisted temporaries, since the child
temporary will not be analyzed up-front. We inherit the hoisted-ness
state and emit the hoisted child temporary as necessary. When faking the
temporaries with OpCopyObject, we make sure to block any variable
hoisting.
Hoisting children of PHI variables is fine, since PHIs are not hoisted with
the same framework as other temporaries.
We'll need to force a temporary and mark it as precise.
MSL is a little weird here, but we can piggyback on top of the invariant
float math option here to force fma() operations everywhere.
We have been interchanging spv and SPIRV_Cross_ for a while, which
causes weirdness since we don't explicitly ban SPIRV_Cross identifiers,
as these identifiers are generally used for interface variable
workarounds.
Avoids certain cases of variance between translation units by forcing
every dependent expression of a store to be temporary.
Should avoid the major failure cases where invariance matters.
A lot of changes in spirv-opt output.
Some new invalid SPIR-V was found but most of them were not significant
for SPIRV-Cross, so just marked them as invalid.
