Landing: c29a38d644bb

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Project / Subsystem

gcc / riscv

Date

2026-05-01

Author

Philipp Tomsich

Commit

c29a38d644bb6984875d92acac9b30a133dacd6f

Source

github

Perf win

Yes

Breaking

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All attributes

project: gcc
subsystem: riscv
patch_id: —
commit_hash: c29a38d644bb6984875d92acac9b30a133dacd6f
source_type: github
headline: RISC-V: Optimize power-of-2 boundary comparisons in conditional moves.
tldr: Optimizes conditional moves by converting power-of-2 boundary comparisons into shift-based equality tests.
author: Philipp Tomsich
outcome: committed
performance_win: true
breaking_change: false
series_id: —
series_parts: []
tags: • riscv
• optimization
• conditional move
• code generation
discussion_id_link: —
bugzilla_pr: —
url: https://github.com/gcc-mirror/gcc/commit/c29a38d644bb6984875d92acac9b30a133dacd6f
date: 2026-05-01T00:00:00.000Z

The RISC-V backend optimizes conditional moves by detecting unsigned comparisons against power-of-2 boundaries and converting them to shift-based equality tests. This avoids materializing large constants, replacing them with a single shift instruction. This optimization improves code generation for expressions like (a & (0xff << 56)) ? b : 0.