feat(joinir): Phase 172 - Trim pattern JoinIR lowering implementation
Implement actual MIR generation for Trim pattern loops, enabling LoopBodyLocal variables to work through bool carrier promotion. ## Implementation (pattern2_with_break.rs) - emit_whitespace_check(): Generate OR chain for whitespace comparison - extract_substring_args(): Extract s, start from substring call - Initial carrier generation: ch0 = s.substring(start, start+1) - Whitespace check: is_ch_match0 = (ch0 == " " || "\t" || "\n" || "\r") - ConditionEnv integration: Register carrier for JoinIR condition - Break condition replacement: !is_ch_match instead of original ch checks ## Architecture - Host MIR: substring calls, OR chain evaluation, BoxCall - JoinIR: Only sees bool carrier for break control - No new JoinIR instructions added ## Documentation - phase172-trim-lowering-impl.md: Design and implementation details - loop_pattern_space.md: Analysis of all loop pattern combinations Test: Trim loops compile and generate JoinIR successfully Build: 0 errors, clean compilation 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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nyash-codex
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docs/development/current/main/phase172-trim-lowering-impl.md
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docs/development/current/main/phase172-trim-lowering-impl.md
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# Phase 172: Trim Pattern JoinIR Lowering Implementation
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## Objective
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Implement actual JoinIR → MIR lowering for Trim pattern loops, making `test_trim_main_pattern.hako` work end-to-end.
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## Target Loop
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**File**: `local_tests/test_trim_main_pattern.hako`
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**Leading whitespace trim loop**:
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```nyash
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loop(start < end) {
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local ch = s.substring(start, start+1)
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if ch == " " || ch == "\t" || ch == "\n" || ch == "\r" {
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start = start + 1
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} else {
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break
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}
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}
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```
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## Using Boxes from Phase 171
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### Phase 171 Infrastructure
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- ✅ **LoopConditionScopeBox**: Detects `ch` as LoopBodyLocal
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- ✅ **LoopBodyCarrierPromoter**: Promotes `ch` to bool carrier `is_ch_match`
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- ✅ **TrimPatternInfo**: Contains promotion metadata
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- ✅ **TrimLoopHelper**: Attached to CarrierInfo for lowering guidance
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- ✅ **Pattern2 validation**: Currently returns informative error at line 234-239
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## Design Philosophy
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### Responsibility Separation
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**Host MIR Side** (before/after JoinIR):
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- Execute `substring()` method calls
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- Evaluate OR chain comparisons (`ch == " " || ch == "\t" || ...`)
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- Generate bool result for carrier
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- BoxCall operations
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**JoinIR Side** (pure control flow):
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- bool carrier-based loop control
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- break condition: `!is_ch_match`
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- No knowledge of substring/OR chain
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- No new JoinIR instructions
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### Key Insight
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The Trim pattern transformation:
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```
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Original:
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local ch = s.substring(start, start+1)
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if (ch == " " || ch == "\t" || ...) { start++ } else { break }
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Transformed:
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is_ch_match = (s.substring(start, start+1) == " " || ...) # Host MIR
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if (!is_ch_match) { break } # JoinIR
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```
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## Implementation Steps
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### Step 1: Loop Pre-Initialization (Task 172-2)
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**Location**: `pattern2_with_break.rs`, before JoinIR generation
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**Goal**: Initialize bool carrier before entering loop
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**Implementation**:
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```rust
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// After Line 264 (after carrier_info.merge_from)
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if let Some(helper) = carrier_info.trim_helper() {
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if helper.is_safe_trim() {
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// Generate initial whitespace check
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// ch0 = s.substring(start, start+1)
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let ch0 = self.emit_method_call("substring", s_id, vec![start_id, start_plus_1_id])?;
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// is_ch_match0 = (ch0 == " " || ch0 == "\t" || ...)
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let is_ch_match0 = emit_whitespace_check(self, ch0, &helper.whitespace_chars)?;
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// Update carrier_info initial value
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// (Will be used in JoinIR input mapping)
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}
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}
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```
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**Helper Function** (new):
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```rust
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fn emit_whitespace_check(
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builder: &mut MirBuilder,
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ch_value: ValueId,
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whitespace_chars: &[String],
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) -> Result<ValueId, String> {
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// Build OR chain: ch == " " || ch == "\t" || ...
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let mut result = None;
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for ws_char in whitespace_chars {
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let ws_const = emit_string(builder, ws_char.clone());
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let eq_check = emit_eq_to(builder, ch_value, ws_const)?;
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result = Some(if let Some(prev) = result {
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// prev || eq_check
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emit_binary_op(builder, BinaryOp::Or, prev, eq_check)?
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} else {
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eq_check
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});
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}
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result.ok_or("Empty whitespace_chars".to_string())
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}
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```
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### Step 2: Loop Body Update Logic (Task 172-3)
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**Location**: Pattern2 lowerer's latch generation (after `start = start + 1`)
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**Goal**: Update bool carrier for next iteration
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**Implementation**:
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```rust
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// In latch block generation (conceptually after line 267+)
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if let Some(helper) = carrier_info.trim_helper() {
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if helper.is_safe_trim() {
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// ch_next = s.substring(start_next, start_next+1)
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let ch_next = self.emit_method_call("substring", s_id, vec![start_next, start_next_plus_1])?;
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// is_ch_match_next = (ch_next == " " || ...)
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let is_ch_match_next = emit_whitespace_check(self, ch_next, &helper.whitespace_chars)?;
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// Store for JoinIR latch → header PHI
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// (Will be used in carrier update mapping)
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}
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}
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```
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**Note**: The actual MIR emission happens in **host space**, not JoinIR space. The JoinIR only sees the bool carrier as a loop parameter.
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### Step 3: JoinIR break Condition Replacement (Task 172-4)
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**Location**: `lower_loop_with_break_minimal` call at line 267
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**Goal**: Replace break condition with `!is_ch_match`
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**Current Code**:
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```rust
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let (join_module, fragment_meta) = match lower_loop_with_break_minimal(
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scope,
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condition, // loop condition: start < end
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&break_condition_node, // if condition: ch == " " || ...
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&env,
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&loop_var_name
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) { ... }
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```
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**Modified Approach**:
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```rust
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// Phase 172: Trim pattern special route
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if let Some(helper) = carrier_info.trim_helper() {
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if helper.is_safe_trim() {
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// Create negated carrier check: !is_ch_match
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let carrier_var_node = ASTNode::Variable {
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name: helper.carrier_name.clone(), // "is_ch_match"
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span: Span::unknown(),
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};
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let negated_carrier_check = ASTNode::UnaryOp {
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operator: UnaryOperator::Not,
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operand: Box::new(carrier_var_node),
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span: Span::unknown(),
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};
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// Use negated carrier as break condition
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let (join_module, fragment_meta) = match lower_loop_with_break_minimal(
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scope,
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condition, // start < end (unchanged)
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&negated_carrier_check, // !is_ch_match (REPLACED)
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&env,
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&loop_var_name
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) { ... }
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// Continue with normal merge flow...
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}
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}
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```
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**Critical Design Decision**:
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- The break condition AST is replaced, but the loop condition (`start < end`) remains unchanged
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- JoinIR sees bool carrier as just another loop parameter
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- No new JoinIR instructions needed!
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### Step 4: Carrier Mapping Integration
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**Location**: Boundary setup (line 283-291)
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**Goal**: Ensure bool carrier is properly mapped between host and JoinIR
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**Current boundary setup**:
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```rust
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let mut boundary = JoinInlineBoundary::new_inputs_only(
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vec![ValueId(0)], // JoinIR: loop param
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vec![loop_var_id], // Host: "start"
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);
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boundary.condition_bindings = condition_bindings;
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boundary.exit_bindings = exit_bindings.clone();
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```
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**Enhanced with Trim carrier**:
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```rust
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// Phase 172: Add bool carrier to condition_bindings
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if let Some(helper) = carrier_info.trim_helper() {
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let carrier_host_id = self.variable_map.get(&helper.carrier_name)
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.copied()
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.ok_or_else(|| format!("Carrier '{}' not in variable_map", helper.carrier_name))?;
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let carrier_join_id = alloc_join_value(); // Allocate JoinIR-local ID
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env.insert(helper.carrier_name.clone(), carrier_join_id);
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condition_bindings.push(ConditionBinding {
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name: helper.carrier_name.clone(),
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host_value: carrier_host_id,
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join_value: carrier_join_id,
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});
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}
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```
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## Implementation Constraints
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### What We DON'T Change
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1. **ExitLine Architecture**: No changes to ExitLineReconnector/ExitMetaCollector
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2. **Header PHI Generation**: Existing LoopHeaderPhiBuilder handles bool carrier automatically
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3. **JoinIR Instruction Set**: No new instructions added
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4. **Pattern2 Basic Logic**: Core control flow unchanged
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### What We DO Change
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1. **Pre-loop initialization**: Add bool carrier setup
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2. **Latch update logic**: Add bool carrier update
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3. **Break condition AST**: Replace with `!is_ch_match`
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4. **Condition bindings**: Add bool carrier mapping
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## Testing Strategy
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### E2E Test
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**Command**:
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```bash
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./target/release/hakorune local_tests/test_trim_main_pattern.hako
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```
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**Expected Behavior**:
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- **Before**: Error message "✅ Trim pattern validation successful! ... JoinIR lowering: TODO"
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- **After**: `Result: [hello]` and `PASS: Trimmed correctly`
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### Debug Traces
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**With JoinIR debug**:
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```bash
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NYASH_JOINIR_DEBUG=1 ./target/release/hakorune local_tests/test_trim_main_pattern.hako 2>&1 | grep -E "\[pattern2\]|\[trim\]"
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```
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**Expected log patterns**:
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```
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[pattern2/promotion] LoopBodyLocal detected in condition scope
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[pattern2/promoter] LoopBodyLocal 'ch' promoted to carrier 'is_ch_match'
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[pattern2/trim] Safe Trim pattern detected, bypassing LoopBodyLocal restriction
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[pattern2/trim] Carrier: 'is_ch_match', original var: 'ch', whitespace chars: [" ", "\t", "\n", "\r"]
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[pattern2/trim] Emitting whitespace check initialization
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[pattern2/trim] Replacing break condition with !is_ch_match
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```
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### MIR Validation
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**Dump MIR**:
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```bash
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./target/release/hakorune --dump-mir local_tests/test_trim_main_pattern.hako 2>&1 | less
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```
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**Check for**:
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- Pre-loop: `substring()` call + OR chain comparison
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- Loop header: PHI for `is_ch_match`
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- Loop body: Conditional branch on `!is_ch_match`
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- Loop latch: `substring()` call + OR chain update
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- Exit block: Proper carrier value propagation
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## Success Criteria
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1. ✅ `test_trim_main_pattern.hako` executes without errors
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2. ✅ Output: `Result: [hello]` (correctly trimmed)
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3. ✅ Test result: `PASS: Trimmed correctly`
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4. ✅ `cargo build --release` succeeds with 0 errors
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5. ✅ `cargo test` all tests pass
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6. ✅ No new warnings introduced
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7. ✅ MIR dump shows proper SSA form
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## Implementation Status
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- [ ] Task 172-1: Design document (THIS FILE)
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- [ ] Task 172-2: Loop pre-initialization
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- [ ] Task 172-3: Loop body update logic
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- [ ] Task 172-4: JoinIR break condition replacement
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- [ ] Task 172-5: E2E test validation
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- [ ] Task 172-6: Documentation update
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## Future Work (Out of Scope for Phase 172)
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### Pattern 4 Support
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- Apply same Trim lowering to Pattern 4 (loop with continue)
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- Reuse `emit_whitespace_check()` helper
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### JsonParser Integration
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- Apply to all trim loops in JsonParser._trim
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- Validate with JSON parsing smoke tests
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### P6+ Patterns
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- Complex control flow with Trim-like patterns
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- Multi-carrier bool promotion
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## Notes
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### Why This Design Works
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1. **Minimal Invasiveness**: Changes only affect Trim-specific paths
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2. **Reusability**: `emit_whitespace_check()` can be shared with Pattern 4
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3. **Maintainability**: Clear separation between host MIR and JoinIR concerns
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4. **Testability**: Each step can be validated independently
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### Phase 171 Validation Hook
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Current code (line 234-239) already validates Trim pattern and returns early:
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```rust
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return Err(format!(
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"[cf_loop/pattern2] ✅ Trim pattern validation successful! \
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Carrier '{}' ready for Phase 172 implementation. \
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(Pattern detection: PASS, Safety check: PASS, JoinIR lowering: TODO)",
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helper.carrier_name
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));
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```
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Phase 172 will **replace this early return** with actual lowering logic.
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## References
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- **Phase 171-C**: LoopBodyCarrierPromoter implementation
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- **Phase 171-C-5**: TrimLoopHelper design
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- **Pattern2 Lowerer**: `src/mir/builder/control_flow/joinir/patterns/pattern2_with_break.rs`
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- **Test File**: `local_tests/test_trim_main_pattern.hako`
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