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One of the downsides of V_CNDMASK_B32 on AMD is that you burn the SGPRs on the VCC bool, so if you are selecting between constants, those require extra V_MOV_B32 ops.

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@NOTimothyLottes GLSL bitfieldInsert does something else?

@NOTimothyLottes GLSL bitfieldInsert does something else?

Properties5
typearchive
sourcetwitter
date2025-01-06
tagsarchive, twitter, notimothylottes
description@NOTimothyLottes GLSL bitfieldInsert does something else?

Jan 06, 20251 min read

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  • URL: https://x.com/axelgneiting/status/1876147238508138659
  • Author: Axel Gneiting (@axelgneiting)
  • Posted: 2025-01-06 06:02:13

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1/ @axelgneiting

@NOTimothyLottes

GLSL bitfieldInsert does something else?

2/ @NOTimothyLottes

@axelgneiting

Yeah the GLSL bitfieldInsert() and V_BFI_B32 are different. The HW instruction supports an arbitrary bitmask instead of one generated from just {offset, size}

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  • One of the downsides of V_CNDMASK_B32 on AMD is that you burn the SGPRs on the VCC bool, so if you are selecting between constants, those require extra V_MOV_B32 ops.

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