nir/instr_set: Don't remove matching instruction

We currently assume that the instruction is already inserted and we are
optimizing it away, but in the use case I have where we are hoisting
instructions into a preamble and deduplicating as we go along, that
isn't the case. Move this responsibility onto the caller, which also
makes it a bit clearer what's going on and turns this into something
more similar to an actual set.

Reviewed-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/29873>

src/compiler/nir/nir_instr_set.c

@@ -778,8 +778,6 @@ nir_instr_set_add_or_rewrite(struct set *instr_set, nir_instr *instr,
 
       nir_def_rewrite_uses(def, new_def);
 
-      nir_instr_remove(instr);
-
       return match;
    } else {
       /* otherwise, replace hashed instruction */

src/compiler/nir/nir_opt_cse.c

@@ -47,6 +47,7 @@ nir_opt_cse_impl(nir_function_impl *impl)
       nir_foreach_instr_safe(instr, block) {
          if (nir_instr_set_add_or_rewrite(instr_set, instr, dominates)) {
             progress = true;
+            nir_instr_remove(instr);
          }
       }
    }

src/compiler/nir/nir_opt_gcm.c

@@ -838,8 +838,10 @@ opt_gcm_impl(nir_shader *shader, nir_function_impl *impl, bool value_number)
          continue;
 
       if (nir_instr_set_add_or_rewrite(gvn_set, instr,
-                                       value_number ? NULL : weak_gvn))
+                                       value_number ? NULL : weak_gvn)) {
          state.progress = true;
+         nir_instr_remove(instr);
+      }
    }
    nir_instr_set_destroy(gvn_set);
 

src/compiler/nir/nir_opt_reuse_constants.c

@@ -33,6 +33,7 @@ nir_opt_reuse_constants(nir_shader *shader)
 
             if (nir_instr_set_add_or_rewrite(consts, instr, nir_instrs_equal)) {
                func_progress = true;
+               nir_instr_remove(instr);
             }
          }
       }