Landing: 3cca524e337a

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Project / Subsystem

gcc / i386

Date

2026-07-12

Author

MITSUNARI Shigeo

Commit

3cca524e337a886d479e630c7a3e6aef4656b425

Source

github

Perf win

Yes

Breaking

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All attributes

project: gcc
subsystem: i386
patch_id: —
commit_hash: 3cca524e337a886d479e630c7a3e6aef4656b425
source_type: github
headline: Add BMI2 MULX instruction pattern for efficient highpart multiplication.
tldr: New MULX instruction pattern optimizes high part of unsigned multiplication on BMI2 targets.
author: MITSUNARI Shigeo
outcome: committed
performance_win: true
breaking_change: false
series_id: —
series_parts: []
tags: • i386
• optimization
• bmi2
discussion_id_link: —
bugzilla_pr: —
url: https://github.com/gcc-mirror/gcc/commit/3cca524e337a886d479e630c7a3e6aef4656b425
date: 2026-07-12T00:00:00.000Z

GCC now utilizes the BMI2 MULX instruction to directly compute the high part of an unsigned multiplication, replacing a less efficient sequence involving MULQ and a subsequent move to RDX. This optimization reduces instruction count for operations like 32-bit unsigned division by constants requiring 33-bit magic multipliers, changing the sequence from 4 to 3 instructions on BMI2-capable processors.