[llvm] Point workflow yaml at new docker image (PR #133359)

[George Burgess IV via llvm-commits]

https://github.com/gburgessiv created https://github.com/llvm/llvm-project/pull/133359

WIP; docker image hasn't landed yet (see https://github.com/llvm/llvm-project/pull/133137), but I want to see what wins can be verified/bugs can be found outside-of-production.

>From b67b29f9d7dbe6c9b12b4f0d322b7be41094b36a Mon Sep 17 00:00:00 2001
From: George Burgess IV <george.burgess.iv at gmail.com>
Date: Thu, 27 Mar 2025 20:48:47 -0600
Subject: [PATCH 1/2] .github: rely on new llvm-project checkout

This is now baked into the docker images to speed up
premerge cycle times.
---
 .github/workflows/premerge.yaml | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/.github/workflows/premerge.yaml b/.github/workflows/premerge.yaml
index c488421d37450..951c3273d3f4f 100644
--- a/.github/workflows/premerge.yaml
+++ b/.github/workflows/premerge.yaml
@@ -26,6 +26,11 @@ concurrency:
 jobs:
   premerge-checks-linux:
     name: Linux Premerge Checks (Test Only - Please Ignore Results)
+    defaults:
+      run:
+        # The premerge Linux docker instance keeps a pristine clone of LLVM in
+        # /home/gha/llvm-project; that should be used as our main workdir.
+        working-directory: /home/gha/llvm-project
     if: >-
         github.repository_owner == 'llvm' &&
         (github.event_name != 'pull_request' || github.event.action != 'closed')
@@ -34,7 +39,7 @@ jobs:
       - name: Checkout LLVM
         uses: actions/checkout at 11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
-          fetch-depth: 2
+          path: /home/gha/llvm-project
       - name: Setup ccache
         uses: hendrikmuhs/ccache-action at a1209f81afb8c005c13b4296c32e363431bffea5 # v1.2.17
         with:

>From 2000467934238541a884a9bfe182342b8d464908 Mon Sep 17 00:00:00 2001
From: George Burgess IV <george.burgess.iv at gmail.com>
Date: Thu, 27 Mar 2025 20:49:39 -0600
Subject: [PATCH 2/2] DO NOT COMMIT: tweak premerge to use custom image

For help in testing the prior commit
---
 .github/workflows/premerge.yaml | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/.github/workflows/premerge.yaml b/.github/workflows/premerge.yaml
index 951c3273d3f4f..672894446d541 100644
--- a/.github/workflows/premerge.yaml
+++ b/.github/workflows/premerge.yaml
@@ -35,6 +35,8 @@ jobs:
         github.repository_owner == 'llvm' &&
         (github.event_name != 'pull_request' || github.event.action != 'closed')
     runs-on: llvm-premerge-linux-runners
+    container:
+        image: ghcr.io/gburgessiv/llvm-ci-with-checkout:latest
     steps:
       - name: Checkout LLVM
         uses: actions/checkout at 11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
@@ -52,6 +54,8 @@ jobs:
         # are ready for people to start recieving notifications.
         continue-on-error: true
         run: |
+          ls /home/gha
+          exit 1
           git config --global --add safe.directory '*'
 
           modified_files=$(git diff --name-only HEAD~1...HEAD)
@@ -110,6 +114,7 @@ jobs:
       - name: Compute Projects
         id: vars
         run: |
+          exit 1
           modified_files=$(git diff --name-only HEAD~1...HEAD)
           modified_dirs=$(echo "$modified_files" | cut -d'/' -f1 | sort | uniq)
 
@@ -170,6 +175,7 @@ jobs:
         uses: llvm/actions/install-ninja at main
       - name: Build and Test
         run: |
+          exit 1
           modified_files=$(git diff --name-only HEAD~1...HEAD)
           modified_dirs=$(echo "$modified_files" | cut -d'/' -f1 | sort -u)