Fix JIT rolling build issue with non-JIT changes (#64480)

When uploading a JIT rolling build, use the git hash of the most recent
JIT change, not the git hash that was actually built. This handles the case
where a JIT change kicked off an AzDO pipeline, but the pipeline didn't start
until after one or more additional changes were merged.

The AzDO pipelines appear to fetch with `-depth=20`, which should provide
enough history for almost any case.

Fixes #64392

eng/pipelines/coreclr/templates/build-jit-job.yml

@@ -118,7 +118,7 @@ jobs:
       - script: $(PipScript) install --user --upgrade pip && $(PipScript) install --user azure.storage.blob==12.5.0 --force-reinstall
         displayName: Upgrade Pip to latest and install azure-storage-blob Python package
 
-      - script: $(PythonScript) $(Build.SourcesDirectory)/src/coreclr/scripts/jitrollingbuild.py upload -build_type $(buildConfig) -arch $(archType) -host_os $(osGroup) -git_hash $(Build.SourceVersion)
+      - script: $(PythonScript) $(Build.SourcesDirectory)/src/coreclr/scripts/jitrollingbuild.py upload -build_type $(buildConfig) -arch $(archType) -host_os $(osGroup) -git_hash $(Build.SourceVersion) --use_latest_jit_change
         displayName: Upload JIT to Azure Storage
         env:
           CLRJIT_AZ_KEY: $(clrjit_key1) # secret key stored as variable in pipeline

src/coreclr/scripts/jitrollingbuild.py

@@ -74,6 +74,13 @@
 
 git_hash_help = "git hash"
 
+use_latest_jit_change_help = """\
+Starting with the given git hash, look backwards in the git log for the first change that includes any JIT
+change. We want to ensure that any git hash uploaded to the JIT rolling build store is a JIT change. This
+addresses a problem where Azure DevOps sometimes builds changes that come soon after a JIT change, instead of
+the JIT change itself.
+"""
+
 target_dir_help = "Directory to put the downloaded JIT."
 
 skip_cleanup_help = "Skip intermediate file removal."
@@ -97,6 +104,7 @@
 upload_parser = subparsers.add_parser("upload", description=upload_description, parents=[common_parser])
 
 upload_parser.add_argument("-git_hash", required=True, help=git_hash_help)
+upload_parser.add_argument("--use_latest_jit_change", action="store_true", help=use_latest_jit_change_help)
 upload_parser.add_argument("-az_storage_key", help="Key for the clrjit Azure Storage location. Default: use the value of the CLRJIT_AZ_KEY environment variable.")
 upload_parser.add_argument("--skip_cleanup", action="store_true", help=skip_cleanup_help)
 
@@ -458,6 +466,32 @@ def upload_blob(file, blob_name):
     #        pdb_paths = [os.path.join(pdb_dir, item) for item in os.listdir(pdb_dir) if re.match(r'.*clrjit.*', item)]
     #        files += pdb_paths
 
+    # Figure out which git hash to use for the upload. By default, it is the required coreclr_args.git_hash argument.
+    # However, if "--use_latest_jit_change" is passed, we look backwards in the git log for the nearest git commit
+    # with a JIT change (it could, and often will be, the same as the argument git_hash).
+    jit_git_hash = coreclr_args.git_hash
+
+    if coreclr_args.use_latest_jit_change:
+        # Do all the remaining commands, including a number of 'git' commands including relative paths,
+        # from the root of the runtime repo.
+
+        with ChangeDir(coreclr_args.runtime_repo_location):
+            # Enumerate the last change, starting with the jit_git_hash, that included JIT changes.
+            command = [ "git", "log", "--pretty=format:%H", jit_git_hash, "-1", "--", "src/coreclr/jit/*" ]
+            print("Invoking: {}".format(" ".join(command)))
+            proc = subprocess.Popen(command, stdout=subprocess.PIPE)
+            stdout_change_list, _ = proc.communicate()
+            return_code = proc.returncode
+            change_list_hashes = []
+            if return_code == 0:
+                change_list_hashes = stdout_change_list.decode('utf-8').strip().splitlines()
+
+            if len(change_list_hashes) == 0:
+                print("Couldn't find any JIT changes! Just using the argument git_hash")
+            else:
+                jit_git_hash = change_list_hashes[0]
+                print("Using git_hash {}".format(jit_git_hash))
+
     print("Uploading:")
     for item in files:
         print("  {}".format(item))
@@ -472,7 +506,7 @@ def upload_blob(file, blob_name):
         raise RuntimeError("Missing azure storage package.")
 
     blob_service_client = BlobServiceClient(account_url=az_blob_storage_account_uri, credential=coreclr_args.az_storage_key)
-    blob_folder_name = "{}/{}/{}/{}/{}".format(az_builds_root_folder, coreclr_args.git_hash, coreclr_args.host_os, coreclr_args.arch, coreclr_args.build_type)
+    blob_folder_name = "{}/{}/{}/{}/{}".format(az_builds_root_folder, jit_git_hash, coreclr_args.host_os, coreclr_args.arch, coreclr_args.build_type)
 
     total_bytes_uploaded = 0
 
@@ -684,6 +718,11 @@ def setup_spmi_location_arg(spmi_location):
                             lambda unused: True,
                             "Unable to set git_hash")
 
+        coreclr_args.verify(args,
+                            "use_latest_jit_change",
+                            lambda unused: True,
+                            "Unable to set use_latest_jit_change")
+
         coreclr_args.verify(args,
                             "az_storage_key",
                             lambda item: item is not None,