[RISCV] redundant return-only BB not eliminated

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Project / Subsystem

gcc / gcc

Date

2026-08-30

Proposer

Robert Guthrie <forkbombidable@gmail.com>

Source type

public_inbox

Consensus

Proposed

Sentiment

8/10

Technical tradeoffs

• The author's custom fix is overly specific and might not generalize.
• Incorrectly modifying CFG passes like `try_optimize_cfg` can lead to infinite loops or break other optimizations.

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All attributes

project: gcc
subsystem: gcc
patch_id: —
discussion_id: apSEEAiw9CP262re@bertguix
source_type: public_inbox
title: [RISCV] redundant return-only BB not eliminated
headline: RISCV: redundant return-only BB not eliminated
tldr: A factorial function compiled for RISCV produces an unnecessary return instruction, and the contributor seeks guidance on optimization passes.
proposer: Robert Guthrie <forkbombidable@gmail.com>
consensus: Proposed
outcome: proposed
sentiment_score: 8
technical_tradeoffs: • The author's custom fix is overly specific and might not generalize.
• Incorrectly modifying CFG passes like `try_optimize_cfg` can lead to infinite loops or break other optimizations.
series_id: —
series_role: standalone
series_parts: []
tags: • riscv
• optimization
• compiler-internals
• cfg
url: https://inbox.sourceware.org/gcc/apSEEAiw9CP262re@bertguix
bugzilla_url: —
date: 2026-08-30T00:00:00.000Z

[RISCV] redundant return-only BB not eliminated

The author reports an unnecessary return instruction generated for a RISC-V factorial function due to loop unrolling and fall-through. They investigated optimization passes like ‘bbro’ and ‘cleanup_cfg’ but couldn’t pinpoint the exact pass responsible for not eliminating the redundant basic block. The contributor, new to compiler development, added a custom fix and seeks advice on the correct approach.