[virglrenderer-devel] TGSI to GLSL translator type assumptions

[Gurchetan Singh]

I was wondering about the typing assumptions in vrend_shader.  The
TGSI spec says that "all TGSI instructions, known as opcodes, operate
on arbitrary-precision floating-point four-component vectors."

http://gallium.readthedocs.io/en/latest/tgsi.html

However, some instructions such as UMAD / UMUL / ATOMIMIN have integer
source and destination registers, so I assume these instructions are
exceptions to the spec.

One assumption we make is all temporary registers
(TGSI_FILE_TEMPORARY) are a vector of floats.  We do a lot work making
this assumption hold, with many conversions.  For example, the
following TGSI:

https://pastebin.com/PN8eHDvZ

currently produces this GLSL:

https://pastebin.com/p90gevMA

I'm interested in the possibility of removing the
"float(uintBitsToFloat)" and "int(floatBitsToInt)" steps, since I've
found it to be a source of many bugs.  I would like to produce a GLSL
like this:

https://pastebin.com/fJCqYEjj

By inferring the type of the declarations from the opcodes.  We would
copy the tgsi_full_instruction(s) that are emitted in
iter_instruction, deduce the type of the declarations, and then emit
the declarations and instructions.  Is this advisable?