perf(compiler): extend x86 cg peephole rules

docs/changes/2026-03-29-x86-cg-peephole-rules/README.md

@@ -0,0 +1,27 @@
+# Change: Extend x86 CG peephole rules
+
+- **Status**: Implemented
+- **Date**: 2026-03-29
+- **Tier**: Light
+
+## Overview
+
+Extend the x86 CG peephole pass beyond the original cmp/setcc/test/jcc fold. Add test/setcc simplification, zero-add elimination, adc-zero canonicalization, imm-zero no-op removal, and broader branch folding patterns seen in JIT output.
+
+## Motivation
+
+JIT output analysis revealed additional redundant x86 instruction patterns not covered by the initial peephole rules. These patterns are mechanical artifacts of U256 decomposition and lowering.
+
+## Impact
+
+- Module: `docs/modules/compiler/` (x86 CG peephole only)
+- 2 files changed: `src/compiler/target/x86/x86_cg_peephole.cpp` and `.h`
+- Benchmark geomean: +6.9%, largest wins in synth/GAS (~2.4x), memory_grow_mstore/by32 (~1.8x)
+- Known regressions in small set of memory_grow/nogrow/by1 micro cases (within noise)
+
+## Checklist
+
+- [x] Implementation complete
+- [x] Tests added/updated
+- [ ] Module specs in `docs/modules/` updated (if affected)
+- [x] Build and tests pass