Add additional patch folder for performance patches

CMakeLists.txt

@@ -134,6 +134,11 @@ option(
     the tools every time you update llvm-project."
     ON
 )
+option(
+    APPLY_LLVM_PERFORMANCE_PATCHES
+    "During checkout, apply optional downstream patches to
+    llvm-project to improve performance."
+)
 set(
     FVP_INSTALL_DIR
     "${CMAKE_CURRENT_SOURCE_DIR}/fvp/install" CACHE STRING
@@ -280,24 +285,17 @@ if(NOT (LLVM_TOOLCHAIN_C_LIBRARY STREQUAL llvmlibc)) # libc in a separate repo?
   read_repo_version(${LLVM_TOOLCHAIN_C_LIBRARY} ${LLVM_TOOLCHAIN_C_LIBRARY})
 endif()
 
-# The patches are generated from custom branch, with followin command:
-#   git format-patch -k origin/main
-# The patches apply cleanly against llvm-project commit
-# 327124ece7d59de56ca0f9faa2cd82af68c011b9.
-set(
-    llvm_project_patches
-    ${CMAKE_CURRENT_SOURCE_DIR}/patches/llvm-project/0001-libc-tests-with-picolibc-xfail-one-remaining-test.patch
-    ${CMAKE_CURRENT_SOURCE_DIR}/patches/llvm-project/0002-libc-tests-with-picolibc-disable-large-tests.patch
-    ${CMAKE_CURRENT_SOURCE_DIR}/patches/llvm-project/0003-Disable-failing-compiler-rt-test.patch
-    ${CMAKE_CURRENT_SOURCE_DIR}/patches/llvm-project/0004-libc-tests-with-picolibc-XFAIL-uses-of-atomics.patch
-    ${CMAKE_CURRENT_SOURCE_DIR}/patches/llvm-project/0005-libc-tests-with-picolibc-mark-two-more-large-tests.patch
-)
+set(LLVM_PATCH_COMMAND ${Python3_EXECUTABLE} ${CMAKE_CURRENT_SOURCE_DIR}/cmake/patch_llvm.py ${CMAKE_CURRENT_SOURCE_DIR}/patches/llvm-project)
+if(APPLY_LLVM_PERFORMANCE_PATCHES)
+    set(LLVM_PATCH_COMMAND ${LLVM_PATCH_COMMAND} && ${Python3_EXECUTABLE} ${CMAKE_CURRENT_SOURCE_DIR}/cmake/patch_llvm.py ${CMAKE_CURRENT_SOURCE_DIR}/patches/llvm-project-perf)
+endif()
+
 FetchContent_Declare(llvmproject
     GIT_REPOSITORY https://github.com/llvm/llvm-project.git
     GIT_TAG "${llvmproject_TAG}"
     GIT_SHALLOW "${llvmproject_SHALLOW}"
     GIT_PROGRESS TRUE
-    PATCH_COMMAND git reset --quiet --hard && git clean --quiet --force -dx && git am -k --ignore-whitespace --3way ${llvm_project_patches}
+    PATCH_COMMAND ${LLVM_PATCH_COMMAND}
     # Add the llvm subdirectory later to ensure that
     # LLVMEmbeddedToolchainForArm is the first project declared.
     # Otherwise CMAKE_INSTALL_PREFIX_INITIALIZED_TO_DEFAULT

cmake/patch_llvm.py

@@ -0,0 +1,134 @@
+#!/usr/bin/env python3
+
+"""
+Script to apply a set of patches to llvm-project sources.
+"""
+
+import argparse
+import os
+import pathlib
+import subprocess
+import sys
+
+
+def main():
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument(
+        "patchdir",
+        help="Set of patches to apply. This should be a directory containing one or more ordered *.patch files.",
+    )
+    parser.add_argument(
+        "--llvm_dir",
+        help="Directory of the llvm-project git checkout, if not the current directory.",
+    )
+    parser.add_argument(
+        "--method",
+        choices=["am", "apply"],
+        default="apply",
+        help="Git command to use. git am will add each patch as a commit, whereas git apply will leave patched changes staged.",
+    )
+    parser.add_argument(
+        "--reset",
+        help="Clean and hard reset the repo to a specified commit before patching.",
+    )
+    parser.add_argument(
+        "--restore_on_fail",
+        action="store_true",
+        help="If a patch in a series cannot be applied, restore the original state instead of leaving patches missing. Return code will be 2 instead of 1.",
+    )
+    args = parser.parse_args()
+
+    if args.llvm_dir:
+        git_cmd = ["git", "-C", args.llvm_dir]
+    else:
+        git_cmd = ["git"]
+
+    if args.reset:
+        reset_args = git_cmd + ["reset", "--quiet", "--hard", args.reset]
+        subprocess.check_output(reset_args)
+        clean_args = git_cmd + ["clean", "--quiet", "--force", "-dx", args.reset]
+        subprocess.check_output(clean_args)
+
+    abs_patch_dir = os.path.abspath(args.patchdir)
+    patch_list = list(pathlib.Path(abs_patch_dir).glob("*.patch"))
+    patch_list.sort()
+
+    print(f"Found {len(patch_list)} patches to apply:")
+    print("\n".join(p.name for p in patch_list))
+
+    if args.method == "am":
+        merge_args = git_cmd + ["am", "-k", "--ignore-whitespace", "--3way"]
+        for patch in patch_list:
+            merge_args.append(str(patch))
+        p = subprocess.run(merge_args, capture_output=True, text=True)
+        print(p.stdout)
+        print(p.stderr)
+
+        if p.returncode == 0:
+            print(f"All patches applied.")
+            sys.exit(0)
+        if args.restore_on_fail:
+            # Check that the operation can be aborted.
+            # git am doesn't give any specific return codes,
+            # so check for unresolved working files.
+            rebase_apply_path = os.path.join(".git", "rebase-apply")
+            if args.llvm_dir:
+                rebase_apply_path = os.path.join(args.llvm_dir, rebase_apply_path)
+            if os.path.isdir(rebase_apply_path):
+                print("Aborting git am...")
+                subprocess.run(git_cmd + ["am", "--abort"], check=True)
+                print(f"Abort successful.")
+                sys.exit(2)
+            else:
+                print("Unable to abort.")
+        sys.exit(1)
+    else:
+        applied_patches = []
+        for current_patch in patch_list:
+            print(f"Checking {current_patch.name}...")
+            # Check that the patch applies before trying to apply it.
+            apply_check_args = git_cmd + [
+                "apply",
+                "--ignore-whitespace",
+                "--3way",
+                "--check",
+                str(current_patch),
+            ]
+            p_check = subprocess.run(apply_check_args)
+
+            if p_check.returncode == 0:
+                # Patch will apply.
+                print(f"Applying {current_patch.name}...")
+                apply_args = git_cmd + [
+                    "apply",
+                    "--ignore-whitespace",
+                    "--3way",
+                    str(current_patch),
+                ]
+                apply_args = subprocess.run(apply_args, check=True)
+                applied_patches.append(current_patch)
+            else:
+                # Patch won't apply.
+                print(f"Unable to apply {current_patch.name}")
+                if args.restore_on_fail:
+                    # Remove any patches that have already been applied.
+                    while len(applied_patches) > 0:
+                        previous_patch = applied_patches.pop()
+                        print(f"Reversing {previous_patch.name}...")
+                        reverse_args = git_cmd + [
+                            "apply",
+                            "--ignore-whitespace",
+                            "--3way",
+                            "--reverse",
+                            str(previous_patch),
+                        ]
+                        p_check = subprocess.run(reverse_args, check=True)
+                    print(
+                        f"Rollback successful, failure occured on {current_patch.name}"
+                    )
+                    sys.exit(2)
+                sys.exit(1)
+        print(f"All patches applied.")
+
+
+main()

docs/building-from-source.md

@@ -148,3 +148,12 @@ The same build directory can be used for both native and MinGW toolchains.
 
 See [patches](https://github.com/ARM-software/LLVM-embedded-toolchain-for-Arm/tree/main/patches)
 directory for the current set of differences from upstream.
+
+The patches for llvm-project are split between two folders, llvm-project and
+llvm-project-perf. The former are generally required for building and
+successfully running all tests. The patches in llvm-project-perf are optional,
+and designed to improve performance in certain circumstances.
+
+To reduce divergence from upstream and potential patch conflicts, the
+performance patches are not applied by default, but can be enabled for an
+automatic checkout with the APPLY_LLVM_PERFORMANCE_PATCHES option.

patches/llvm-project-perf/0000-Placeholder-commit.patch

@@ -0,0 +1,22 @@
+From e79697a54cba9bfc1a755ed048e42054d679de61 Mon Sep 17 00:00:00 2001
+From: David Candler <[email protected]>
+Date: Wed, 2 Oct 2024 14:13:31 +0100
+Subject: [PATCH] Placeholder commit
+
+---
+ .gitignore | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/.gitignore b/.gitignore
+index 0e7c6c790013..dfa0b8da0ccd 100644
+--- a/.gitignore
++++ b/.gitignore
+@@ -1,4 +1,4 @@
+-#==============================================================================#
++#==============================================================================#
+ # This file specifies intentionally untracked files that git should ignore.
+ # See: http://www.kernel.org/pub/software/scm/git/docs/gitignore.html
+ #
+-- 
+2.34.1
+