[Driver] Mark -arch as TargetSpecific

[MaskRay]

-arch is a Darwin-specific option that is ignored for other targets
and not known by GCC.

% clang -arch arm64 -c a.c
clang: warning: argument unused during compilation: '-arch arm64' [-Wunused-command-line-argument]

We are utilizing TargetSpecific (from https://reviews.llvm.org/D151590)
to make more options lead to errors for unsupported targets.

[llvmbot]

@llvm/pr-subscribers-clang-driver

@llvm/pr-subscribers-clang

Author: Fangrui Song (MaskRay)

Changes

-arch is a Darwin-specific option that is ignored for other targets
and not known by GCC.

% clang -arch arm64 -c a.c
clang: warning: argument unused during compilation: '-arch arm64' [-Wunused-command-line-argument]

We are utilizing TargetSpecific (from https://reviews.llvm.org/D151590)
to make more options lead to errors for unsupported targets.

---

Full diff: https://github.com/llvm/llvm-project/pull/74365.diff

4 Files Affected:

• (modified) clang/include/clang/Driver/Options.td (+1-1)
• (modified) clang/test/Driver/arc-exceptions.m (+2-2)
• (modified) clang/test/Driver/arm-arch-darwin.c (+3-2)
• (modified) clang/test/Frontend/darwin-eabi.c (+3-3)

diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index 1d04e4f6e7e6d..8c6d1f61ebcf2 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -994,7 +994,7 @@ def all__load : Flag<["-"], "all_load">;
 def allowable__client : Separate<["-"], "allowable_client">;
 def ansi : Flag<["-", "--"], "ansi">, Group<CompileOnly_Group>;
 def arch__errors__fatal : Flag<["-"], "arch_errors_fatal">;
-def arch : Separate<["-"], "arch">, Flags<[NoXarchOption]>;
+def arch : Separate<["-"], "arch">, Flags<[NoXarchOption,TargetSpecific]>;
 def arch__only : Separate<["-"], "arch_only">;
 def autocomplete : Joined<["--"], "autocomplete=">;
 def bind__at__load : Flag<["-"], "bind_at_load">;
diff --git a/clang/test/Driver/arc-exceptions.m b/clang/test/Driver/arc-exceptions.m
index 4501ccd073823..c1dd02d59988c 100644
--- a/clang/test/Driver/arc-exceptions.m
+++ b/clang/test/Driver/arc-exceptions.m
@@ -1,5 +1,5 @@
-// RUN: %clang -### -x objective-c -arch x86_64 -fobjc-arc -fsyntax-only %s 2> %t.log
+// RUN: %clang -### -x objective-c --target=x86_64-apple-macos10.6 -fobjc-arc -fsyntax-only %s 2> %t.log
 // RUN: grep objective-c %t.log
 // RUN: not grep "fobjc-arc-exceptions" %t.log
-// RUN: %clang -### -x objective-c++ -arch x86_64 -fobjc-arc -fsyntax-only %s 2> %t.log
+// RUN: %clang -### -x objective-c++ --target=x86_64-apple-macos10.6 -fobjc-arc -fsyntax-only %s 2> %t.log
 // RUN: grep "fobjc-arc-exceptions" %t.log
diff --git a/clang/test/Driver/arm-arch-darwin.c b/clang/test/Driver/arm-arch-darwin.c
index 55089619d1e71..c523622964738 100644
--- a/clang/test/Driver/arm-arch-darwin.c
+++ b/clang/test/Driver/arm-arch-darwin.c
@@ -1,6 +1,7 @@
 // On Darwin, arch should override CPU for triple purposes
 // RUN: %clang -target armv7m-apple-darwin -arch armv7m -mcpu=cortex-m4 -### -c %s 2>&1 | FileCheck -check-prefix=CHECK-V7M-DARWIN %s
 // CHECK-V7M-DARWIN: "-cc1"{{.*}} "-triple" "thumbv7m-{{.*}} "-target-cpu" "cortex-m4"
-// RUN: %clang -target armv7m -arch armv7m -mcpu=cortex-m4 -### -c %s 2>&1 | FileCheck -check-prefix=CHECK-V7M-OVERRIDDEN %s
-// CHECK-V7M-OVERRIDDEN: "-cc1"{{.*}} "-triple" "thumbv7em-{{.*}} "-target-cpu" "cortex-m4"
 
+/// -arch is unsupported for non-Darwin targets.
+// RUN: not %clang --target=armv7m -arch armv7m -mcpu=cortex-m4 -### -c %s 2>&1 | FileCheck -check-prefix=ERR %s
+// ERR: unsupported option '-arch' for target 'armv7m'
diff --git a/clang/test/Frontend/darwin-eabi.c b/clang/test/Frontend/darwin-eabi.c
index 27471e6cfb0e6..9d62632891cbe 100644
--- a/clang/test/Frontend/darwin-eabi.c
+++ b/clang/test/Frontend/darwin-eabi.c
@@ -1,6 +1,6 @@
-// RUN: %clang -arch armv6m -dM -E %s | FileCheck %s
-// RUN: %clang -arch armv7m -dM -E %s | FileCheck %s
-// RUN: %clang -arch armv7em -dM -E %s | FileCheck %s
+// RUN: %clang --target=armv6m-apple-darwin -dM -E %s | FileCheck %s
+// RUN: %clang --target=armv7m-apple-darwin -dM -E %s | FileCheck %s
+// RUN: %clang --target=armv7em-apple-darwin -dM -E %s | FileCheck %s
 // RUN: %clang_cc1 -triple thumbv7m-apple-unknown-macho -dM -E %s | FileCheck %s
 
 // CHECK-NOT: __ENVIRONMENT_IPHONE_OS_VERSION_MIN_REQUIRED__

[kovdan01]

@MaskRay Unfortunately, the case I was initially trying to fix still has a problem after applying this patch. Consider LLVM_DEFAULT_TARGET_TRIPLE=aarch64-linux-musl. In such a case, running clang -arch arm64e -c test.c -### will show us "-triple" "aarch64-unknown-linux-musl". As far as I understood from the comment #72821 (comment), a warning -Wunused-command-line-argument should be emitted - but it is not (this does not change even if we really compile to the object file instead of just printing cli args with -###).

Are we supposed to pass -target to clang in addition to -arch if we want to be sure to compile with Apple's triple? It might be reasonable, but in such case many tests which use -arch without -target actually might run with undesired non-Apple triple - I find such behavior a bit misleading. Is this "by design"?

[MaskRay]

When the target triple is aarch64 and -arch is specified, e.g. --target=aarch64 -arch arm64e, there is currently no warning/error, because clang/lib/Driver/ToolChains/Arch/AArch64.cpp claims OPT_arch in quite a few places.
We can safely remove these references now that https://reviews.llvm.org/D55731 has checked isOSDarwin (which covers macOS/iOS/watchOS/DriverKit).

Are we supposed to pass -target to clang in addition to -arch if we want to be sure to compile with Apple's triple?

If the default target triple is not Apple's triple, --target= is required. clang -arch arm64 without --target= does not work.
This is the desired behavior.

It might be reasonable, but in such case many tests which use -arch without -target actually might run with undesired non-Apple triple - I find such behavior a bit misleading. Is this "by design"?

These tests need to be fixed to specify --target= if it may run on a non-Apple target.
It's possible that -arch is redundant with --target=.

[kovdan01]

OK, thanks for such a detailed explanation! Closing #72821 as not needed.