compact compiler ids and spans to reduce memory usage

benchmarks/symbols/README.md

@@ -29,3 +29,9 @@ The measured run reduced token size by 14.3% and peak tracked memory by 9.8%.
 After the iterative compiler-hardening work on 2026-06-12, the same benchmark
 reported 13,222,443 peak bytes and 40,117 allocations. The reusable traversal
 stacks keep allocation count effectively unchanged from the interning baseline.
+
+After migrating persistent compiler references and spans to compact IDs on
+2026-06-12, the benchmark reported 8,651,659 peak bytes and 40,117 allocations.
+`Span` is 12 bytes and `Token` is 24 bytes; AST expressions, HIR expressions,
+and IR instructions are 64, 88, and 88 bytes respectively. These sizes are
+also printed by the benchmark to catch layout regressions.

benchmarks/symbols/main.odin

@@ -3,6 +3,7 @@ package main
 import "../../compiler/ast"
 import "../../compiler/checker"
 import "../../compiler/hir"
+import "../../compiler/ir"
 import "../../compiler/lexer"
 import "../../compiler/parser"
 import "../../compiler/source"
@@ -72,6 +73,10 @@ main :: proc() {
 	fmt.printf("allocation_count: %d\n", tracker.total_allocation_count)
 	fmt.printf("token_count: %d\n", metrics.token_count)
 	fmt.printf("token_size_bytes: %d\n", size_of(token.Token))
+	fmt.printf("span_size_bytes: %d\n", size_of(source.Span))
+	fmt.printf("ast_expr_size_bytes: %d\n", size_of(ast.Expr))
+	fmt.printf("hir_expr_size_bytes: %d\n", size_of(hir.Expr))
+	fmt.printf("ir_instruction_size_bytes: %d\n", size_of(ir.Instruction))
 	fmt.printf("unique_symbol_count: %d\n", metrics.unique_symbol_count)
 	fmt.printf("stored_symbol_bytes: %d\n", metrics.stored_symbol_bytes)
 	fmt.printf("diagnostic_count: %d\n", metrics.diagnostic_count)