aco/opt: Rename loop header phis

Fossil stats on top of !35269:
Totals from 133 (0.16% of 81077) affected shaders:

Instrs: 4328456 -> 4327891 (-0.01%)
CodeSize: 22890004 -> 22887732 (-0.01%); split: -0.01%, +0.00%
Latency: 28406452 -> 28404732 (-0.01%)
InvThroughput: 5361458 -> 5361153 (-0.01%)
Copies: 376788 -> 376222 (-0.15%)
VALU: 2429210 -> 2428645 (-0.02%)
VOPD: 57 -> 56 (-1.75%)
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/35270>

src/amd/compiler/aco_optimizer.cpp

@@ -4994,6 +4994,29 @@ validate_opt_ctx(opt_ctx& ctx)
    }
 }
 
+void rename_loop_header_phis(opt_ctx& ctx) {
+   for (Block& block : ctx.program->blocks) {
+      if (!(block.kind & block_kind_loop_header))
+         continue;
+
+      for (auto& instr : block.instructions) {
+         if (!is_phi(instr))
+            break;
+
+         for (unsigned i = 0; i < instr->operands.size(); i++) {
+            if (!instr->operands[i].isTemp())
+               continue;
+
+            ssa_info info = ctx.info[instr->operands[i].tempId()];
+            while (info.is_temp()) {
+               pseudo_propagate_temp(ctx, instr, info.temp, i);
+               info = ctx.info[info.temp.id()];
+            }
+         }
+      }
+   }
+}
+
 } /* end namespace */
 
 void
@@ -5012,6 +5035,10 @@ optimize(Program* program)
 
    validate_opt_ctx(ctx);
 
+   rename_loop_header_phis(ctx);
+
+   validate_opt_ctx(ctx);
+
    ctx.uses = dead_code_analysis(program);
 
    /* 2. Rematerialize constants in every block. */