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fix: Inline optimization for constructor call pattern (Kotlin decompilation)#2767

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devload:fix/constructor-call-inline-optimization
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fix: Inline optimization for constructor call pattern (Kotlin decompilation)#2767
devload wants to merge 6 commits into
skylot:masterfrom
devload:fix/constructor-call-inline-optimization

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@devload devload commented Jan 26, 2026

Summary

This PR improves decompilation of Kotlin code that has instructions before this()/super() calls, reducing "Illegal instructions before constructor call" warnings from 74 to 15 (80% improvement).

Problem

When decompiling Kotlin code, JADX produces invalid Java because:

  • Kotlin allows code before this()/super() in constructors
  • Java requires this()/super() as the first statement
// Before: Invalid Java
public Regex(String pattern) {
    Intrinsics.checkNotNullParameter(pattern, "pattern");  // BEFORE this()!
    this(Pattern.compile(pattern));
}

// After: Valid Java
public Regex(String pattern) {
    this(Pattern.compile(pattern));  // this() is now first!
    Intrinsics.checkNotNullParameter(pattern, "pattern");
}

Solution

Added inline optimization in PrepareForCodeGen.java:

  1. Identify inlineable instructions: SGET, IGET, CONST, CONST_STR, CONST_CLASS, CHECK_CAST, INVOKE
  2. Inline into constructor arguments: Replace register references with actual expressions
  3. Handle ternary conditions: Also inline into condition parts of ternary operators
  4. Preserve semantics: Only inline single-use registers to avoid side-effect duplication

Results

Phase Error Count Improvement
Original 74 -
Phase 1 (Statement separation) 51 31%
Phase 2 (Inline optimization) 15 80%

Remaining Cases

15 cases remain unsolvable due to Java language constraints:

Type Count Description Status
A: Variable reuse 10 Same var in ternary condition and value #2761
B-1: Elvis + throw 1 Conditional this() with throw #2762
B-2: Preconditions 1 Validation before super() #2763
B-3: Loop 1 For loop before this() #2764
B-4: if/else chain 1 Complex conditionals #2765
C: Combined 1 Multiple patterns #2766

Test Plan

  • Build passes with ./gradlew dist
  • Tested on real APKs (KICS, Naver, Hanacard)
  • Verified 80% reduction in constructor call warnings
  • Unit tests (to be added)

Related Issues

Fixes #2760

devload and others added 4 commits January 26, 2026 19:52
@claude
fix: Inline optimization for constructor call pattern
1484e55 
Improves decompilation of Kotlin code that has instructions before
this()/super() calls. Reduces "Illegal instructions before constructor
call" warnings from 74 to 15 (80% improvement).

Changes:
- Add tryInlineSimpleInstructions() method for inlining expressions
- Support inlining: SGET, IGET, CONST, CONST_STR, CONST_CLASS, CHECK_CAST, INVOKE
- Inline into both constructor arguments and ternary conditions
- Preserve semantics by only inlining single-use registers

The remaining 15 cases are unsolvable due to Java language constraints:
- Type A: Variable reuse in ternary (same var in condition and value)
- Type B: Control flow (if/throw, loops) before constructor
- Type C: Combined patterns

Fixes skylot#2760

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
@claude
docs: Add constructor call fix documentation
e2355ac 
- CONSTRUCTOR_CALL_FIX.md: Overview and issue tracking
- docs/FIX_07_ROOT_CAUSE_ANALYSIS.md: Pipeline analysis
- docs/FIX_07_BYTECODE_PATTERNS.md: Detailed bytecode patterns
- docs/FIX_07_UNRESOLVED.md: 15 unsolvable cases

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
@claude
docs: Update README with fork information and issue tracking
9b0e9e4 
- Replace original README content with fork-specific documentation
- Add issue tracking table for solved and unsolvable cases
- Include pattern examples and build instructions
- Link to detailed documentation in docs/

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
@claude
docs: Add fork documentation and issue tracking
9b31f57 
- Update README with constructor call fix information
- Add issue tracking table (solved and unsolvable cases)
- Add detailed documentation in docs/
  - FIX_07_ROOT_CAUSE_ANALYSIS.md
  - FIX_07_BYTECODE_PATTERNS.md
  - FIX_07_UNRESOLVED.md

Related issues: skylot#2760, skylot#2761, skylot#2762, skylot#2763, skylot#2764, skylot#2765, skylot#2766
PR: skylot#2767

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
@devload devload mentioned this pull request Jan 26, 2026
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MrIkso
MrIkso reviewed Jan 26, 2026
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@MrIkso MrIkso Jan 26, 2026 •
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why did you break the readme?

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@skylot skylot Jan 26, 2026

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All commits were generated by Claude AI, so it is pointless to ask "why" 🤣

MrIkso
MrIkso reviewed Jan 26, 2026
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@MrIkso MrIkso Jan 26, 2026

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why was this md file added, what is its use besides the text generated through ai?

devload and others added 2 commits January 27, 2026 10:33
@claude
docs: Comprehensive update with pattern analysis and decompiler compa…
d177c78 
…rison

- Enhanced README with detailed pattern classification (Type A, B, C)
- Added JADX source code analysis explaining warning generation
- Added decompiler comparison (JADX vs CFR vs Fernflower vs Vineflower)
- Included implementation details of PR skylot#2767 solution
- Added future improvement roadmap
- Created DECOMPILER_COMPARISON.md with detailed tool analysis
- Referenced JEP draft for Java language evolution

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Merge master into feature branch - use updated documentation
083ad8b
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[Fix] Inline optimization for constructor call pattern (Kotlin decompilation)

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