7c55baa818
- Created joinir_function_converter.rs (~133 lines): Function-level conversion - Created joinir_block_converter.rs (~691 lines): Block-level conversion - Reduced convert.rs from 943 → 120 lines (87% reduction) - Total: 944 lines (original 943 lines, minimal overhead) - Separation of concerns: Function vs Block responsibilities - All handlers moved to block_converter for better organization - Maintained backward compatibility with existing API - Build successful, simple tests passing
142 lines
3.0 KiB
Markdown
142 lines
3.0 KiB
Markdown
# Phase 33-11: Exit Block PHI Node Missing Bug Analysis
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## Problem Summary
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The MIR generated from JoinIR lowering is missing PHI nodes in the exit block, causing "use of undefined value" errors.
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## Test Case
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File: `apps/tests/loop_min_while.hako`
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```nyash
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static box Main {
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main() {
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local i = 0
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loop(i < 3) {
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print(i)
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i = i + 1
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}
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return 0
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}
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}
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```
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## Error
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```
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[ERROR] use of undefined value ValueId(16)
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```
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## MIR Dump Analysis
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```mir
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bb8:
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1: ret %16 # %16 is never defined!
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```
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bb8 is the exit block, but ValueId(16) is never defined anywhere.
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## Root Cause
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In `src/mir/builder/control_flow.rs::merge_joinir_mir_blocks()`:
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### Step 1: Exit block is created empty (line 618-621)
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```rust
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let exit_block_id = self.block_gen.next();
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// ...
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let exit_block = BasicBlock::new(exit_block_id); // Empty!
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func.add_block(exit_block);
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```
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### Step 2: Return instructions are converted to Jump (line 827-841)
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```rust
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MirInstruction::Return { value } => {
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if let Some(ret_val) = value {
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let remapped_val = value_map.get(ret_val).copied().unwrap_or(*ret_val);
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if debug {
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eprintln!(
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"[cf_loop/joinir] Return({:?}) → Jump to exit",
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remapped_val
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);
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}
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}
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MirInstruction::Jump {
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target: exit_block_id,
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}
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}
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```
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**Problem**: The return value (`remapped_val`) is logged but NOT STORED anywhere!
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### Step 3: Exit block stays empty
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The exit block is never populated with:
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- PHI nodes to collect return values
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- Return instruction to return the PHI'd value
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## Expected Fix
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The exit block should look like:
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```mir
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bb8:
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1: %16 = phi [%9 from bb7], [%2 from bb5], ...
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1: ret %16
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```
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Or simpler, if all functions return the same constant:
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```mir
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bb8:
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1: %16 = const 0
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1: ret %16
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```
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## JoinIR Functions Structure
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The Pattern 1 lowerer generates 3 functions:
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1. **main()**: Calls loop_step, returns 0
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2. **loop_step()**: Tail recursion OR Jump to k_exit
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3. **k_exit()**: Returns 0
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All Return instructions are converted to Jump to bb8 (exit block).
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## Solution Strategy
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### Option A: Collect Return Values + Generate PHI
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1. While converting Return→Jump, collect all return values
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2. After merging, generate PHI node in exit block
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3. Add Return instruction that returns PHI result
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### Option B: Direct Value Propagation
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1. Since Pattern 1 always returns 0, directly emit const 0 in exit block
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2. Simpler but less general
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### Option C: Track Return Values in Hash Map
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1. Create `HashMap<BasicBlockId, ValueId>` to track returns
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2. Use as PHI incoming values
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3. Most robust, handles all patterns
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## Recommendation
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Start with **Option B** (simplest fix for Pattern 1), then generalize to **Option C** for future patterns.
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## Implementation Location
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File: `src/mir/builder/control_flow.rs`
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Function: `merge_joinir_mir_blocks()`
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Lines: ~827-950
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## Test Validation
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```bash
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NYASH_DISABLE_PLUGINS=1 ./target/release/hakorune apps/tests/loop_min_while.hako
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```
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Expected output:
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```
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0
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1
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2
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```
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