aco: skip value numbering of copies

Instead, copy-propagate through and remove them.

This improves value numbering in this situation:
a = ...
b = copy a
c = copy a
use(b)
use(c)

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7216>

src/amd/compiler/aco_opt_value_numbering.cpp

@@ -393,6 +393,7 @@ void process_block(vn_ctx& ctx, Block& block)
           !instr->definitions[0].isFixed() && instr->operands[0].isTemp() && instr->operands[0].regClass() == instr->definitions[0].regClass() &&
           !instr->isDPP() && !((int)instr->format & (int)Format::SDWA)) {
          ctx.renames[instr->definitions[0].tempId()] = instr->operands[0].getTemp();
+         continue;
       }
 
       instr->pass_flags = ctx.exec_id;