feat(phase-91): JoinIR Selfhost depth-2 advancement - Pattern P5b design & planning

## Overview Analyzed 34 loops across selfhost codebase to identify JoinIR coverage gaps. Current readiness: 47% (16/30 loops). Next frontier: Pattern P5b (Escape Handling). ## Current Status - Phase 91 planning document: Complete - Loop inventory across 6 key files - Priority ranking: P5b (escape) > P5 (guard) > P6 (nested) - Effort estimates and ROI analysis - Pattern P5b Design: Complete - Problem statement (variable-step carriers) - Pattern definition with Skeleton layout - Recognition algorithm (8-step detection) - Capability taxonomy (P5b-specific guards) - Lowering strategy (Phase 92 preview) - Test fixture: Created - Minimal escape sequence parser - JSON string with backslash escape - Loop Canonicalizer extended - Capability table updated with P5b entries - Fail-Fast criteria documented - Implementation checklist added ## Key Findings ### Loop Readiness Matrix | Category | Count | JoinIR Status | |----------|-------|--------------| | Pattern 1 (simple bounded) | 16 | ✅ Ready | | Pattern 2 (with break) | 1 | ⚠️ Partial | | **Pattern P5b (escape seq)** | ~3 | ❌ NEW | | Pattern P5 (guard-bounded) | ~2 | ❌ Deferred | | Pattern P6 (nested loops) | ~8 | ❌ Deferred | ### Top Candidates 1. **P5b**: json_loader.hako:30 (8 lines, high reuse) - Effort: 2-3 days (recognition) - Impact: Unlocks all escape parsers 2. **P5**: mini_vm_core.hako:541 (204 lines, monolithic) - Effort: 1-2 weeks - Impact: Major JSON optimization 3. **P6**: seam_inspector.hako:76 (7+ nesting) - Effort: 2-3 weeks - Impact: Demonstrates nested composition ## Phase 91 Strategy **Recognition-only phase** (no lowering in P1): - Step 1: Design & planning ✅ - Step 2: Canonicalizer implementation (detect_escape_pattern) - Step 3: Unit tests + parity verification - Step 4: Lowering deferred to Phase 92 ## Files Added - docs/development/current/main/phases/phase-91/README.md - Full analysis & planning - docs/development/current/main/design/pattern-p5b-escape-design.md - Technical design - tools/selfhost/test_pattern5b_escape_minimal.hako - Test fixture ## Files Modified - docs/development/current/main/design/loop-canonicalizer.md - Capability table extended with P5b entries - Pattern P5b full section added - Implementation checklist updated ## Acceptance Criteria (Phase 91 Step 1) - ✅ Loop inventory complete (34 loops across 6 files) - ✅ Pattern P5b design document ready - ✅ Test fixture created - ✅ Capability taxonomy extended - ⏳ Implementation deferred (Step 2+) ## References - JoinIR Architecture: joinir-architecture-overview.md - Phase 91 Plan: phases/phase-91/README.md - P5b Design: design/pattern-p5b-escape-design.md Next: Implement detect_escape_pattern() recognition in Phase 91 Step 2 🤖 Generated with Claude Code Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>
2025-12-16 14:22:36 +09:00
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+# Phase 91: JoinIR Coverage Expansion (Selfhost depth-2)
+
+## Status
+- 🔍 **Analysis Complete**: Loop inventory across selfhost codebase
+- 📋 **Planning**: Pattern P5b (Escape Handling) candidate selected
+- ⏳ **Implementation**: Deferred to dedicated session
+
+## Executive Summary
+
+**Current JoinIR Readiness**: 47% (16/30 loops in selfhost code)
+
+| Category | Count | Status | Effort |
+|----------|-------|--------|--------|
+| Pattern 1 (simple bounded) | 16 | ✅ Ready | None |
+| Pattern 2 (with break) | 1 | ⚠️ Partial | Low |
+| Pattern P5b (escape handling) | ~3 | ❌ Blocked | Medium |
+| Pattern P5 (guard-bounded) | ~2 | ❌ Blocked | High |
+| Pattern P6 (nested loops) | ~8 | ❌ Blocked | Very High |
+
+---
+
+## Analysis Results
+
+### Loop Inventory by Component
+
+#### File: `apps/selfhost-vm/boxes/json_cur.hako` (3 loops)
+- Lines 9-14: ✅ Pattern 1 (simple bounded)
+- Lines 23-32: ✅ Pattern 1 variant with break
+- Lines 42-57: ✅ Pattern 1 with guard-less loop(true)
+
+#### File: `apps/selfhost-vm/json_loader.hako` (3 loops)
+- Lines 16-22: ✅ Pattern 1 (simple bounded)
+- **Lines 30-37**: ❌ Pattern P5b **CANDIDATE** (escape sequence handling)
+- Lines 43-48: ✅ Pattern 1 (simple bounded)
+
+#### File: `apps/selfhost-vm/boxes/mini_vm_core.hako` (9 loops)
+- Lines 208-231: ⚠️ Pattern 1 variant (with continue)
+- Lines 239-253: ✅ Pattern 1 (with accumulator)
+- Lines 388-400, 493-505: ✅ Pattern 1 (6 bounded search loops)
+- **Lines 541-745**: ❌ Pattern P5 **PRIME CANDIDATE** (guard-bounded, 204-line collect_prints)
+
+#### File: `apps/selfhost-vm/boxes/seam_inspector.hako` (13 loops)
+- Lines 10-26: ✅ Pattern 1
+- Lines 38-42, 116-120, 123-127: ✅ Pattern 1 variants
+- **Lines 76-107**: ❌ Pattern P6 (deeply nested, 7+ levels)
+- Remaining: Mix of ⚠️ Pattern 1 variants with nested loops
+
+#### File: `apps/selfhost-vm/boxes/mini_vm_prints.hako` (1 loop)
+- Line 118+: ❌ Pattern P5 (guard-bounded multi-case)
+
+---
+
+## Candidate Selection: Priority Order
+
+### 🥇 **IMMEDIATE CANDIDATE: Pattern P5b (Escape Handling)**
+
+**Target**: `json_loader.hako:30` - `read_digits_from()`
+
+**Scope**: 8-line loop
+
+**Current Structure**:
+```nyash
+loop(i < n) {
+  local ch = s.substring(i, i+1)
+  if ch == "\"" { break }
+  if ch == "\\" {
+    i = i + 1
+    ch = s.substring(i, i+1)
+  }
+  out = out + ch
+  i = i + 1
+}
+```
+
+**Pattern Classification**:
+- **Header**: `loop(i < n)`
+- **Escape Check**: `if ch == "\\" { i = i + 2 instead of i + 1 }`
+- **Body**: Append character
+- **Carriers**: `i` (position), `out` (buffer)
+- **Challenge**: Variable increment (sometimes +1, sometimes +2)
+
+**Why This Candidate**:
+- ✅ **Small scope** (8 lines) - good for initial implementation
+- ✅ **High reuse potential** - same pattern appears in multiple parser locations
+- ✅ **Moderate complexity** - requires conditional step extension (not fully generic)
+- ✅ **Clear benefit** - would unlock escape sequence handling across all string parsers
+- ❌ **Scope limitation** - conditional increment not yet in Canonicalizer
+
+**Effort Estimate**: 2-3 days
+- Canonicalizer extension: 4-6 hours
+- Pattern recognizer: 2-3 hours
+- Lowering implementation: 4-6 hours
+- Testing + verification: 2-3 hours
+
+---
+
+### 🥈 **SECOND CANDIDATE: Pattern P5 (Guard-Bounded)**
+
+**Target**: `mini_vm_core.hako:541` - `collect_prints()`
+
+**Scope**: 204-line loop (monolithic)
+
+**Current Structure**:
+```nyash
+loop(true) {
+  guard = guard + 1
+  if guard > 200 { break }
+
+  local p = index_of_from(json, k_print, pos)
+  if p < 0 { break }
+
+  // 5 different cases based on JSON type
+  if is_binary_op { ... pos = ... out.push(...) }
+  if is_compare { ... pos = ... out.push(...) }
+  if is_literal { ... pos = ... out.push(...) }
+  if is_function_call { ... pos = ... out.push(...) }
+  if is_nested { ... pos = ... out.push(...) }
+
+  pos = obj_end + 1
+}
+```
+
+**Pattern Classification**:
+- **Header**: `loop(true)` (unconditional)
+- **Guard**: `guard > LIMIT` with increment each iteration
+- **Body**: Multiple case-based mutations
+- **Carriers**: `pos`, `printed`, `guard`, `out` (ArrayBox)
+- **Exit conditions**: Guard exhaustion OR search failure
+
+**Why This Candidate**:
+- ✅ **Monolithic optimization opportunity** - 204 lines of complex control flow
+- ✅ **Real-world JSON parsing** - demonstrates practical JoinIR application
+- ✅ **High performance impact** - guard counter could be eliminated via SSA
+- ❌ **High complexity** - needs new Pattern5 guard-handling variant
+- ❌ **Large scope** - would benefit from split into micro-loops first
+
+**Effort Estimate**: 1-2 weeks
+- Design: 2-3 days (pattern definition, contract)
+- Implementation: 5-7 days
+- Testing + verification: 2-3 days
+
+**Alternative Strategy**: Could split into 5 micro-loops per case:
+```nyash
+// Instead of one 204-line loop with 5 cases:
+// Create 5 functions, each handling one case:
+loop_binary_op() { ... }
+loop_compare() { ... }
+loop_literal() { ... }
+loop_function_call() { ... }
+loop_nested() { ... }
+
+// Then main loop dispatches:
+loop(true) {
+  guard = guard + 1
+  if guard > limit { break }
+  if type == BINARY_OP { loop_binary_op(...) }
+  ...
+}
+```
+
+This would make each sub-loop Pattern 1-compatible immediately.
+
+---
+
+### 🥉 **THIRD CANDIDATE: Pattern P6 (Nested Loops)**
+
+**Target**: `seam_inspector.hako:76` - `_scan_boxes()`
+
+**Scope**: Multi-level nested (7+ nesting levels)
+
+**Current Structure**: 37-line outer loop containing 6 nested loops
+
+**Pattern Classification**:
+- **Nesting levels**: 7+
+- **Carriers**: Multiple per level (`i`, `j`, `k`, `name`, `pos`, etc.)
+- **Exit conditions**: Varied per level (bounds, break, continue)
+- **Scope handoff**: Complex state passing between levels
+
+**Why This Candidate**:
+- ✅ **Demonstrates nested composition** - needed for production parsers
+- ✅ **Realistic code** - actual box/function scanner
+- ❌ **Highest complexity** - requires recursive JoinIR composition
+- ❌ **Long-term project** - 2-3 weeks minimum
+
+**Effort Estimate**: 2-3 weeks
+- Design recursive composition: 3-5 days
+- Per-level implementation: 7-10 days
+- Testing nested composition: 3-5 days
+
+---
+
+## Recommended Immediate Action
+
+### Phase 91 (This Session): Pattern P5b Planning
+
+**Objective**: Design Pattern P5b (escape sequence handling) with minimal implementation
+
+**Steps**:
+1. ✅ **Analysis complete** (done by Explore agent)
+2. **Design P5b pattern** (canonicalizer contract)
+3. **Create minimal fixture** (`test_pattern5b_escape_minimal.hako`)
+4. **Extend Canonicalizer** to recognize escape patterns
+5. **Plan lowering** (defer implementation to next session)
+6. **Document P5b architecture** in loop-canonicalizer.md
+
+**Acceptance Criteria**:
+- ✅ Pattern P5b design document complete
+- ✅ Minimal escape test fixture created
+- ✅ Canonicalizer recognizes escape patterns (dev-only observation)
+- ✅ Parity check passes (strict mode)
+- ✅ No lowering changes yet (recognition-only phase)
+
+**Deliverables**:
+- `docs/development/current/main/phases/phase-91/README.md` - This document
+- `docs/development/current/main/design/pattern-p5b-escape-design.md` - Pattern design (new)
+- `tools/selfhost/test_pattern5b_escape_minimal.hako` - Test fixture (new)
+- Updated `docs/development/current/main/design/loop-canonicalizer.md` - Capability tags extended
+
+---
+
+## Design: Pattern P5b (Escape Sequence Handling)
+
+### Motivation
+
+String parsing commonly requires escape sequence handling:
+- Double quotes: `"text with \" escaped quote"`
+- Backslashes: `"path\\with\\backslashes"`
+- Newlines: `"text with \n newline"`
+
+Current loops handle this with conditional increment:
+```rust
+if ch == "\\" {
+    i = i + 1  // Skip escape character itself
+    ch = next_char
+}
+i = i + 1  // Always advance
+```
+
+This variable-step pattern is **not JoinIR-compatible** because:
+- Loop increment is conditional (sometimes +1, sometimes +2)
+- Canonicalizer expects constant-delta carriers
+- Lowering expects uniform update rules
+
+### Solution: Pattern P5b Definition
+
+#### Header Requirement
+```
+loop(i < n)  // Bounded loop on string length
+```
+
+#### Escape Check Requirement
+```
+if ch == "\\" {
+    i = i + delta_skip  // Skip character (typically +1, +2, or variable)
+    // Optional: consume escape character
+    ch = s.substring(i, i+1)
+}
+```
+
+#### After-Escape Requirement
+```
+// Standard character processing
+out = out + ch
+i = i + delta_normal  // Standard increment (typically +1)
+```
+
+#### Skeleton Structure
+```
+LoopSkeleton {
+  steps: [
+    HeaderCond(i < n),
+    Body(escape_check_stmts),
+    Body(process_char_stmts),
+    Update(i = i + normal_delta, maybe(i = i + skip_delta))
+  ]
+}
+```
+
+#### Carrier Configuration
+- **Primary Carrier**: Loop variable (`i`)
+  - `delta_normal`: +1 (standard case)
+  - `delta_escape`: +1 or +2 (skip escape)
+- **Secondary Carrier**: Accumulator (`out`)
+  - Pattern: `out = out + value`
+
+#### ExitContract
+```
+ExitContract {
+  has_break: true,   // Break on quote detection
+  has_continue: false,
+  has_return: false,
+  carriers: vec![
+    CarrierInfo { name: "i", deltas: [+1, +2] },
+    CarrierInfo { name: "out", pattern: Append }
+  ]
+}
+```
+
+#### Routing Decision
+```
+RoutingDecision {
+  chosen: Pattern5bEscape,
+  structure_notes: ["escape_handling", "variable_step"],
+  missing_caps: []  // All required capabilities present
+}
+```
+
+### Recognition Algorithm
+
+#### AST Inspection Steps
+
+1. **Find escape check**:
+   - Pattern: `if ch == "\\" { ... }`
+   - Extract: Escape character constant
+   - Extract: Increment inside if block
+
+2. **Extract skip delta**:
+   - Pattern: `i = i + <const>`
+   - Calculate: `skip_delta = <const>`
+
+3. **Find normal increment**:
+   - Pattern: `i = i + <const>` (after escape if block)
+   - Calculate: `normal_delta = <const>`
+
+4. **Validate break condition**:
+   - Pattern: `if <char> == "<quote>" { break }`
+   - Required for string boundary detection
+
+5. **Build LoopSkeleton**:
+   - Carriers: `[{name: "i", deltas: [normal, skip]}, ...]`
+   - ExitContract: `has_break=true`
+   - RoutingDecision: `chosen=Pattern5bEscape`
+
+### Implementation Plan
+
+#### Canonicalizer Extension (`src/mir/loop_canonicalizer/canonicalizer.rs`)
+
+Add `detect_escape_pattern()` recognition:
+```rust
+fn detect_escape_pattern(
+    loop_expr: &Expr,
+    carriers: &[String]
+) -> Option<EscapePatternInfo> {
+    // Step 1-5 as above
+    // Return: { escape_char, skip_delta, normal_delta, carrier_name }
+}
+```
+
+Priority: Call before `detect_skip_whitespace_pattern()` (more specific pattern first)
+
+#### Pattern Recognizer Wrapper (`src/mir/loop_canonicalizer/pattern_recognizer.rs`)
+
+Expose `detect_escape_pattern()`:
+```rust
+pub fn try_extract_escape_pattern(
+    loop_expr: &Expr
+) -> Option<(String, i64, i64)> {  // (carrier, normal_delta, skip_delta)
+    // Delegate to canonicalizer detection
+}
+```
+
+#### Test Fixture (`tools/selfhost/test_pattern5b_escape_minimal.hako`)
+
+Minimal reproducible example:
+```nyash
+// Minimal escape sequence parser
+local s = "\\"hello\\" world"
+local n = s.length()
+local i = 0
+local out = ""
+
+loop(i < n) {
+  local ch = s.substring(i, i+1)
+
+  if ch == "\"" {
+    break
+  }
+
+  if ch == "\\" {
+    i = i + 1  // Skip escape character
+    if i < n {
+      ch = s.substring(i, i+1)
+    }
+  }
+
+  out = out + ch
+  i = i + 1
+}
+
+print(out)  // Should print: hello" world
+```
+
+---
+
+## Files to Modify (Phase 91)
+
+### New Files
+1. `docs/development/current/main/phases/phase-91/README.md` ← You are here
+2. `docs/development/current/main/design/pattern-p5b-escape-design.md` (new - detailed design)
+3. `tools/selfhost/test_pattern5b_escape_minimal.hako` (new - test fixture)
+
+### Modified Files
+1. `docs/development/current/main/design/loop-canonicalizer.md`
+   - Add Pattern P5b to capability matrix
+   - Add recognition algorithm
+   - Add routing decision table
+
+2. (Phase 91 Step 2+) `src/mir/loop_canonicalizer/canonicalizer.rs`
+   - Add `detect_escape_pattern()` function
+   - Extend `canonicalize_loop_expr()` to check for escape patterns
+
+3. (Phase 91 Step 2+) `src/mir/loop_canonicalizer/pattern_recognizer.rs`
+   - Add `try_extract_escape_pattern()` wrapper
+
+---
+
+## Next Steps (Future Sessions)
+
+### Phase 91 Step 2: Implementation
+- Implement `detect_escape_pattern()` in Canonicalizer
+- Add unit tests for escape pattern recognition
+- Verify strict parity with router
+
+### Phase 92: Lowering
+- Implement Pattern5bEscape lowerer
+- Handle variable-step carrier updates
+- E2E test with `test_pattern5b_escape_minimal.hako`
+
+### Phase 93: Pattern P5 (Guard-Bounded)
+- Implement Pattern5 for `mini_vm_core.hako:541`
+- Consider micro-loop refactoring alternative
+- Document guard-counter optimization strategy
+
+### Phase 94+: Pattern P6 (Nested Loops)
+- Recursive JoinIR composition for `seam_inspector.hako:76`
+- Cross-level scope/carrier handoff
+
+---
+
+## SSOT References
+
+- **JoinIR Architecture**: `docs/development/current/main/joinir-architecture-overview.md`
+- **Loop Canonicalizer Design**: `docs/development/current/main/design/loop-canonicalizer.md`
+- **Capability Tags**: `src/mir/loop_canonicalizer/capability_guard.rs`
+
+---
+
+## Summary
+
+**Phase 91** establishes the next frontier of JoinIR coverage: **Pattern P5b (Escape Handling)**.
+
+This pattern unlocks:
+- ✅ All string escape parsing loops
+- ✅ Foundation for Pattern P5 (guard-bounded)
+- ✅ Preparation for Pattern P6 (nested loops)
+
+**Current readiness**: 47% (16/30 loops)
+**After Phase 91**: Expected to reach ~60% (18/30 loops)
+**Long-term target**: >90% coverage with P5, P5b, P6 patterns
+
+All acceptance criteria defined. Implementation ready for next session.