[4.5:r99336] Cortex-A8 optimisation: jump/loop alignment.

Bug #628907 reported by Andrew Stubbs
8
This bug affects 1 person
Affects Status Importance Assigned to Milestone
Linaro GCC Tracking
Invalid
Undecided
Andrew Stubbs

Bug Description

Related: lp:gcc-linaro/4.5,revno=99336

Cortex-A8 optimisation: jump/loop alignment.

Merged from SourceryG++

Tags: 46merge
Revision history for this message
Andrew Stubbs (ams-codesourcery) wrote :

Assigning upstream submission to Julian.

affects: gcc-linaro → gcc-linaro-tracking
Changed in gcc-linaro-tracking:
assignee: nobody → Julian Brown (julian-codesourcery)
milestone: none → 4.6.0
tags: added: 46merge
Changed in gcc-linaro-tracking:
milestone: 4.6.0 → 4.7.0
Revision history for this message
Andrew Stubbs (ams-codesourcery) wrote :

I've benchmarked this patch on A8 (imx51) using "-O3 -static -mcpu=cortex-a8" in GCC 4.6 and found *no* measurable speed improvement.

In fact, I've benchmarked every permutation of -falign-functions={4,8,16,32,64} and -falign-jumps={4,8,16,32,64}, and found that none of them give a measurable improvement.

Therefore, I suggest dropping this patch on A8, and possibly on A9 also, if the benchmark results turn out the same.

Revision history for this message
Andrew Stubbs (ams-codesourcery) wrote :

Benchmarking on A9 shows little better results. There are a few configurations that give a tiny improvement, but they're far from consistent across all the benchmark instances.

I'm going to drop this patch.

Changed in gcc-linaro-tracking:
assignee: Julian Brown (julian-codesourcery) → Andrew Stubbs (ams-codesourcery)
milestone: 4.7.0 → rejected
status: New → Won't Fix
Changed in gcc-linaro-tracking:
status: Won't Fix → Invalid
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