Landing: 0b12c7345a94

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Project / Subsystem

gcc / rtl-optimization

Date

2026-04-26

Author

Roger Sayle

Commit

0b12c7345a94f11bdacf360d45b847307f9be9cf

Source

github

Perf win

Yes

Breaking

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project: gcc
subsystem: rtl-optimization
patch_id: —
commit_hash: 0b12c7345a94f11bdacf360d45b847307f9be9cf
source_type: github
headline: rtl-optimization: Simplify vec_select of a vec_select.
tldr: GCC now simplifies consecutive vector permutations, reducing redundant instructions and improving code generation for vector operations.
author: Roger Sayle
outcome: committed
performance_win: true
breaking_change: false
series_id: —
series_parts: []
tags: • optimization
• rtl
• vectorization
• code generation
discussion_id_link: —
bugzilla_pr: —
url: https://github.com/gcc-mirror/gcc/commit/0b12c7345a94f11bdacf360d45b847307f9be9cf
date: 2026-04-26T00:00:00.000Z

GCC’s RTL optimizer now simplifies vec_select operations applied consecutively. When the output of one vec_select instruction feeds directly into another, the compiler combines them into a single vec_select with an equivalent permutation. This removes redundant shuffle instructions, leading to more compact and efficient code, particularly for vector-heavy operations. This optimisation avoids a sequence of permutes by collapsing them into a single permute.