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MaxXSoft
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Oct 20, 2026
MaxXSoft
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- Coauthored by: GPT-6 Astra
- Reviewed by: MaxXing
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🟢 Approval recommended
Static review and the reported standalone stack-model check found no blocking issues; project simulations were not run.
No open issues 🎉
What changed in this PR
Adds a speculative 16-entry return-address stack to improve return prediction alongside the existing branch predictor.
Changes:
- Recognizes standard and compressed call/return hints, with backend-flush recovery.
- Adds stack, predictor, fetch, and core integration tests to CI.
- Documents RAS behavior and consolidates instruction constants.
| File | Description |
|---|---|
| src/test/scala/core/stages/FetchRasTest.scala | Tests stalls, nested returns, flushes, and faults. |
| src/test/scala/core/integration/CoreRasTest.scala | Tests return prediction and retirement under stalls. |
| src/test/scala/bpu/ReturnAddressStackTest.scala | Tests stack boundaries and randomized operations. |
| src/test/scala/bpu/RasPredictionTest.scala | Tests instruction hints and prediction fallback. |
| src/test/scala/bpu/DecoderTrainingTest.scala | Initializes new predictor inputs. |
| src/test/scala/bpu/BranchPredictorTest.scala | Initializes new predictor inputs. |
| src/main/scala/core/Fetch.scala | Connects instruction acceptance and flush signals. |
| src/main/scala/core/Decoder.scala | Adds whitespace only. |
| src/main/scala/core/CompressedDecoder.scala | Uses shared constants and explicit opcodes. |
| src/main/scala/consts/Parameters.scala | Defines RAS capacity. |
| src/main/scala/consts/Instructions.scala | Adds a shared EBREAK encoding. |
| src/main/scala/bpu/ReturnAddressStack.scala | Implements the bounded speculative stack. |
| src/main/scala/bpu/BranchPredictor.scala | Adds call/return predecode and RAS prediction. |
| README.md | Documents RAS behavior and recovery limitations. |
| CHANGELOG.md | Records the RAS addition. |
| .github/workflows/test.yml | Runs the new regression tests. |
Review effort: Balanced
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