aco: Mark exec write used when it writes other registers.

When an exec write isn't used but writes other registers
besides exec, and also reads exec (such as s_and_saveexec),
we would mistakenly delete the previous instruction that
writes the exec value that this instruction uses.

No Fossil DB changes on Rembrandt (GFX10.3).

Fixes: 0211e66f65
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/9036
Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Georg Lehmann <dadschoorse@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/23576>

src/amd/compiler/aco_ssa_elimination.cpp

@@ -604,9 +604,10 @@ eliminate_useless_exec_writes_in_block(ssa_elimination_ctx& ctx, Block& block)
          bool writes_other = std::any_of(instr->definitions.begin(), instr->definitions.end(),
                                          [](const Definition& def) -> bool
                                          { return def.physReg() != exec && def.physReg() != scc; });
-         if (!writes_other)
+         if (!writes_other) {
             instr.reset();
-         continue;
+            continue;
+         }
       }
 
       /* For a newly encountered exec write, clear the used flag. */