Bug 1747533 - Update clang pass manager flags handling. r=firefox-build-system-reviewers,andi

- Avoid the flag selection silently not enabling the new pass manager
  when --enable-new-pass-manager is passed explicitly.
- Avoid adding the -fexperimental-new-pass-manager to clang >= 13, which
  has it enabled by default. Likewise for the linker flags.
- Remove the force-enable of the new pass manager with clang < 12 on
  automation, since we're using version 13 anyways.
- Account for the fact that both lld and ld64 can pass the
  -import-hot-multiplier flag to the LTO plugin on mac builds, which
  effectively will set it for the first time on mac, and might improve
  performance.

Differential Revision: https://phabricator.services.mozilla.com/D134860

build/moz.configure/flags.configure

@@ -35,32 +35,68 @@ option(
     enable_fuzzing,
     ubsan,
 )
-def new_pass_manager_flags(enabled, compiler, host, target, pgo, enable_fuzzing, ubsan):
+def pass_manager(enabled, compiler, host, target, pgo, enable_fuzzing, ubsan):
+    if compiler.type not in ("clang", "clang-cl"):
+        return None
+
+    # As of clang 13, the default pass manager is the new one.
+    if compiler.version >= "13.0.0":
+        if enabled:
+            return namespace(flags=None, enabled=True)
+        if compiler.type == "clang":
+            return namespace(flags=["-flegacy-pass-manager"], enabled=False)
+        if compiler.type == "clang-cl":
+            return namespace(flags=["-Xclang", "-flegacy-pass-manager"], enabled=False)
+
+    if not enabled:
+        return None
+    if compiler.version < "9.0.0":
+        if enabled.origin != "default":
+            die("--enable-new-pass-manager is only supported with clang >= 9")
+        return None
+
     if host.os == "OSX":
         # Some native Mac builds hang with the new pass manager. Given the
         # inability to test in CI, don't take the risk of further breakage.
+        if enabled.origin != "default":
+            die(
+                "--enable-new-pass-manager causes problems on mac hosts with clang < 13"
+            )
         return None
     if target.os == "OSX" and not pgo:
         # Also disable when cross-compiling to Mac, because plain-ish opt
         # builds hang. Variants like asan and ccov work fine, but it would be
         # too tedious to test them all here. PGO is the only thing that matters
         # enough to make an exception for.
+        if enabled.origin != "default":
+            die(
+                "--enable-new-pass-manager causes problems on mac builds with clang < 13"
+            )
         return None
     if enable_fuzzing and compiler.version < "10.0.0":
         # Clang 9 does not seem to play well with libFuzzer
+        if enabled.origin != "default":
+            die(
+                "--enable-new-pass-manager causes problems on fuzzing builds with clang < 10"
+            )
         return None
     if ubsan and compiler.version == "10.0.0":
         # Clang 10.0.0 hangs with some ubsan-inserted code constructs.
         # This was fixed in 10.0.1 (https://llvm.org/pr45835)
+        if enabled.origin != "default":
+            die(
+                "--enable-new-pass-manager causes problems with ubsan builds with clang 10.0.0"
+            )
         return None
-    if enabled and compiler.version >= "9.0.0":
-        if compiler.type == "clang":
-            return ["-fexperimental-new-pass-manager"]
-        elif compiler.type == "clang-cl":
-            return ["-Xclang", "-fexperimental-new-pass-manager"]
+    if compiler.type == "clang":
+        return namespace(flags=["-fexperimental-new-pass-manager"], enabled=True)
+    elif compiler.type == "clang-cl":
+        return namespace(
+            flags=["-Xclang", "-fexperimental-new-pass-manager"], enabled=True
+        )
 
 
-set_config("MOZ_NEW_PASS_MANAGER_FLAGS", new_pass_manager_flags)
+set_config("MOZ_PASS_MANAGER_FLAGS", pass_manager.flags)
 
 
 # Try to make builds more reproducible and allow sharing built artifacts across

build/moz.configure/lto-pgo.configure

@@ -183,22 +183,20 @@ imply_option("MOZ_LD64_KNOWN_GOOD", depends_if("MOZ_AUTOMATION")(lambda _: True)
     "--enable-lto",
     c_compiler,
     select_linker,
-    "MOZ_AUTOMATION",
     "MOZ_LD64_KNOWN_GOOD",
     target,
     "--enable-profile-generate",
-    new_pass_manager_flags,
+    pass_manager.enabled,
 )
 @imports("multiprocessing")
 def lto(
     value,
     c_compiler,
     select_linker,
-    automation,
     ld64_known_good,
     target,
     instrumented_build,
-    newpm_flags,
+    pass_manager,
 ):
     cflags = []
     ldflags = []
@@ -234,6 +232,7 @@ def lto(
         target.kernel == "Darwin"
         and target.os == "OSX"
         and value == "cross"
+        and select_linker.KIND == "ld64"
         and not ld64_known_good
     ):
         die(
@@ -315,15 +314,17 @@ def lto(
     # If we're using the new pass manager, we can also enable the new PM
     # during LTO. Further we can use the resulting size savings to increase
     # the import limit in hot functions.
-    if newpm_flags:
+    if pass_manager:
         if target.os == "WINNT":
-            # On Windows, this flag requires a change from clang-12, which
-            # is applied as a patch to our automation toolchain.
-            if automation or c_compiler.version >= "12.0.0":
+            if c_compiler.version >= "12.0.0" and c_compiler.version < "13.0.0":
                 ldflags.append("-opt:ltonewpassmanager")
+            if c_compiler.version >= "12.0.0":
                 ldflags.append("-mllvm:-import-hot-multiplier=30")
-        elif select_linker.KIND != "ld64" and c_compiler.type == "clang":
-            ldflags.append("-Wl,-plugin-opt=new-pass-manager")
+        elif target.os == "OSX":
+            ldflags.append("-Wl,-mllvm,-import-hot-multiplier=30")
+        else:
+            if c_compiler.version < "13.0.0":
+                ldflags.append("-Wl,-plugin-opt=new-pass-manager")
             ldflags.append("-Wl,-plugin-opt=-import-hot-multiplier=30")
 
     return namespace(

python/mozbuild/mozbuild/frontend/context.py

@@ -655,8 +655,8 @@ class CompileFlags(TargetCompileFlags):
                 ("CXXFLAGS", "CFLAGS"),
             ),
             (
-                "NEWPM",
-                context.config.substs.get("MOZ_NEW_PASS_MANAGER_FLAGS"),
+                "PASS_MANAGER",
+                context.config.substs.get("MOZ_PASS_MANAGER_FLAGS"),
                 ("CXXFLAGS", "CFLAGS"),
             ),
             (