mem: Fix a RAR/RAWQueue bug.

[Ergou-ren]

The current load/storeCompletedIdx ignores certain situations, which may cause some instructions before Idx to not have been committed.

Change-Id: I7f79ad2ea0bc305f9d389e4372b45a453bf59278

Summary by CodeRabbit

• Refactor
  • Refined completion tracking logic in queue management systems to improve state consistency and boundary handling for more reliable operation sequencing.

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[coderabbitai]

📝 Walkthrough

Walkthrough

The LSQ unit's completion index tracking mechanism was refactored to use a sentinel convention (head()-1) for initialized indices, enforce strict boundary constraints, replace per-iteration progression with guarded advancement loops, and introduce a unified rewindCompletedIdx mechanism to handle squash operations consistently.

Changes

Cohort / File(s)	Summary
LSQ Unit Completion Index Tracking src/cpu/o3/lsq_unit.cc	Refactored completion index initialization to use head()-1 as sentinel value; added boundary enforcement in updateCompletedIdx; replaced direct progression logic with guarded loops that only advance when queues are non-empty and entries are valid/ready; introduced unified rewindCompletedIdx lambda to handle squash-time boundary restoration for both load and store queues

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~50 minutes

Suggested reviewers

• happy-lx
• jensen-yan
• tastynoob

Poem

🐰 Queues once tangled, now aligned,
Sentinels guard each weary line,
Boundaries held, no squash in sight,
Completion tracking—shining bright! ✨

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately reflects the main change: fixing a bug in RAR/RAWQueue load/storeCompletedIdx handling, which is the core focus of the modifications to lsq_unit.cc.

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✨ Finishing touches

• 📝 Generate docstrings

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[coderabbitai]

Actionable comments posted: 2

🤖 Fix all issues with AI agents

In `@src/cpu/o3/lsq_unit.cc`:
- Around line 2904-2917: The loop that advances loadCompletedIdx can call
loadQueue.getIterator(loadCompletedIdx + 1) when loadCompletedIdx equals the
queue tail, producing an invalid iterator; before calling getIterator(check),
add a bounds check using loadQueue.tail() or loadQueue.size() to ensure
loadCompletedIdx + 1 is within the queue range (e.g., if (loadCompletedIdx + 1
<= loadQueue.tail()) ) and only then obtain loadIt and inspect
loadIt->valid()/instruction()/isExecuted(); keep the rest of the logic
(loadCompletionWidth, DPRINTF, incrementing loadCompletedIdx) unchanged.
- Around line 2920-2932: The loop advances storeCompletedIdx by calling
storeQueue.getIterator(storeCompletedIdx + 1) without checking bounds; when
storeCompletedIdx == storeQueue.tail() that +1 access is out of range. Fix by
adding a bounds check before calling getIterator (or change the loop condition)
so you only attempt getIterator(storeCompletedIdx + 1) when storeCompletedIdx !=
storeQueue.tail(); i.e., ensure the loop over storeCompletionWidth also verifies
storeCompletedIdx != storeQueue.tail() and break if it is, before using
storeQueue.getIterator, keeping use of storeQueue, storeCompletedIdx,
storeCompletionWidth, storeQueue.getIterator, addrReady(), and canWB() intact.

[github-actions]

🚀 Coremark Smoke Test Results

Branch	IPC	Change
Base (xs-dev)	2.1739	-
This PR	2.1739	➡️ 0.0000 (0.00%)

✅ Difftest smoke test passed!