[cpunion]

Problem

ReorderLocals updates Wasm instructions but leaves DW_OP_WASM_location operands pointing at the old local indices. Execution remains correct, but the debugger can silently show another variable's value.

extern int touch(int);
volatile int observed;
__attribute__((noinline)) int run(void) {
  int a = touch(11);
  int b = touch(22);
  int c = touch(33);
  observed = a;
  observed = b;
  observed = c;
  observed = b;
  observed = b;
  return a + b + c; // Inspect a, b, c here after wasm-opt -O1 -g.
}

Check	Before	After
GDB / LLDB: a, b, c	22, 11, 33	11, 22, 33
Program result	66	66
Deleted local	Can point at an unrelated surviving local	Unavailable

The interactive comparison includes #9194 on both sides to separate this bug from the independent line-table problems. The DWARF change is based on main (5d31e56e); its regression tests do not depend on the other DWARF PRs.

CI dependency: temporarily includes Thomas Lively's approved FuzzTest update from #9394. It fixes the uintptr_t error in Abseil that also fails on main. This dependency can be dropped by rebasing once #9394 lands.

Fix

Compose input-to-IR local mappings across reordering and coalescing, then apply the writer's final binary-local mapping to DWARF locations. This also handles the coalescing performed internally by Asyncify. Coalescing's existing DWARF-invalidating status remains: repairing indices does not repair changed variable live ranges.

Rewrite inline expressions and location lists, including shared suffixes, nested expressions and expression-level DIE/type references. If an operand grows across a LEB boundary, relocate the affected list offsets, DIE references, CU lengths and public-name tables. Collection, expression/layout relocation and public-table updates are separate stages. With unchanged CU address sizes, the common same-width case skips the .debug_info layout pass; expressions without DIE references are not decoded again on subsequent iterations. Instruction boundaries use a small ordered vector instead of per-instruction hash allocations. No optimization is disabled.

The implementation is in wasm-debug.cpp. Input list offsets retain the original CU address width; emitted list offsets and DIE layout use the final width. Expressions being rewritten reject truncated operands.

Validation

• All 19 focused DWARF tests pass. Coverage includes repeated passes, StackIR, removed locals, coalescing, LEB boundaries, legacy forms, short-form overflow, multiple CUs, shared list heads/suffixes, expression-level references, Memory64 lowering and truncated operands. The new suffix and expression-reference checks also reproduce failures in the initial PR implementation, before this follow-up fix. Independent LLVM verification is used when available; typed operations unsupported by that verifier still have exact operand and structural assertions.
• All 102 Python tests and the wasm-opt pass suite pass; 455 C++ tests pass, with one existing Linux-only size test skipped on macOS. The Python run excludes V8-dependent checks because local d8 is not V8. The full build and these automated checks were rerun after rebasing onto current main on November 14.
• TinyGo output passes LLVM DWARF verification; O1 + Asyncify runs and prints {"name":"dwarf","value":42}. GDB on Linux arm64 and LLDB on macOS arm64 read the correct values in the combined verification above.

TinyGo sample on the original main baseline (82439ad0), seven alternating warmed runs on macOS arm64; timings are medians, not evidence of a speedup:

Configuration	Output bytes, before → after	wasm-opt time, before → after
O1 + Asyncify, no debug	1,791,971 → 1,791,971	727.4 → 730.6 ms
O1, debug	1,912,371 → 1,912,371	353.0 → 362.6 ms
O1 + Asyncify, debug	2,185,951 → 2,185,947	924.5 → 884.0 ms

Stripped outputs are byte-identical in all three configurations. This fixes local-index relocation, not all remaining DWARF limitations or variable live-range transformations.

Developed with AI assistance; the validation above was executed locally.

[tlively]

Thanks for the PR. I'll remove myself as a reviewer because I won't be able to review this effectively due to lack of DWARF expertise. As an alternative approach, you could skip passes that reorder locals, e.g. with --skip-pass=coalesce-locals.

I've left some notes below about bugs Gemini found, though.

[cpunion]

Thanks for the review. Fixed both bugs and moved the implementation into wasm-debug.cpp in ca64016. I kept remapping so ReorderLocals remains available with DWARF.

Rebased onto current main. All 102 Python tests, 455 C++ tests and the wasm-opt pass suite pass. The new Memory64 and truncated-operand regressions fail before the fixes and pass after them.

[cpunion]

The failed fuzztest job hits the same Abseil uintptr_t error on main. Rebased on current main and included Thomas Lively's approved fix from #9394, preserving authorship. The DWARF changes are unchanged.

All 17 jobs in the new CI run now pass, including clang with fuzztest. Local tests and lint also pass. The temporary CI dependency is noted in the PR body.