[llvm] [Github] Use zstd to compress CI container images (PR #166879)

[Aiden Grossman via llvm-commits]

https://github.com/boomanaiden154 created https://github.com/llvm/llvm-project/pull/166879

zstd usually offers better compression ratios, but also offers much higher decompression speeds, which can tangibly impact image unpack times. Enable this by default given it is a two line change that is transparent at image pull time given most container runtimes these days supported zstd compressed images.

>From ccd576d4704f0697f83ba370b00241d8ee330120 Mon Sep 17 00:00:00 2001
From: Aiden Grossman <aidengrossman at google.com>
Date: Fri, 7 Nov 2025 01:53:06 +0000
Subject: [PATCH] [Github] Use zstd to compress CI container images

zstd usually offers better compression ratios, but also offers much
higher decompression speeds, which can tangibly impact image unpack
times. Enable this by default given it is a two line change that is
transparent at image pull time given most container runtimes these days
supported zstd compressed images.
---
 .github/actions/push-container/action.yml | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/.github/actions/push-container/action.yml b/.github/actions/push-container/action.yml
index 51f4b2aa0002e..087e3dcb2718c 100644
--- a/.github/actions/push-container/action.yml
+++ b/.github/actions/push-container/action.yml
@@ -24,9 +24,9 @@ runs:
           latest_name=$(echo $image_name | sed 's/:[a-f0-9]\+$/:latest/g')
           podman tag $image_name $latest_name
           echo "Pushing $image_name ..."
-          podman push $image_name
+          podman push --compression-format=zstd $image_name
           echo "Pushing $latest_name ..."
-          podman push $latest_name
+          podman push --compression-format=zstd $latest_name
         }
 
         podman login -u ${{ github.actor }} -p $GITHUB_TOKEN ghcr.io