[clang] clang -mpopcnt hello.c <link flag> fails to generate warning when file precedes link flag

[paparodeo]

on aarch64 darwin using the -mpopcnt flag will result in a warning on clang 16 and error on clang 19.1.3. however, if a linker flag trails the file name no warning / error is generated. eg:

$ clang -mpopcnt hello.c -lc
$ ./a.out
hello world

however, re-ordering the command line so the file name comes after -lc will generate the expected error

$ clang -mpopcnt -lc hello.c
clang: error: unsupported option '-mpopcnt' for target 'aarch64-apple-darwin'

this behavior is not seen with all link flags, eg -flat_namespace always will generate an error, but when used in conjunction with -Wl will generate an error (as do other flags, like -v)

$ clang -mpopcnt -flat_namespace hello.c
clang: error: unsupported option '-mpopcnt' for target 'aarch64-apple-darwin'
$ clang -mpopcnt hello.c -flat_namespace
clang: error: unsupported option '-mpopcnt' for target 'aarch64-apple-darwin'
$ clang -mpopcnt -Wl,-flat_namespace hello.c
clang: error: unsupported option '-mpopcnt' for target 'aarch64-apple-darwin'
$ clang -mpopcnt hello.c -Wl,-flat_namespace
$ ./a.out
hello world

$ clang -v
clang version 19.1.3
Target: aarch64-apple-darwin24.1.0
Thread model: posix
InstalledDir: /nix/store/6b4vxqc16xq1nq8jhdsylfml244vah22-clang-19.1.3/bin

[llvmbot]

@llvm/issue-subscribers-clang-driver

Author: Reno Dakota (paparodeo)

on aarch64 darwin using the `-mpopcnt` flag will result in a warning on clang 16 and error on clang 19.1.3. however, if a linker flag trails the file name no warning / error is generated. eg:

$ clang -mpopcnt hello.c -lc
$ ./a.out
hello world

however, re-ordering the command line so the file name comes after -lc will generate the expected error

$ clang -mpopcnt -lc hello.c
clang: error: unsupported option '-mpopcnt' for target 'aarch64-apple-darwin'

this behavior is not seen with all link flags, eg -flat_namespace always will generate an error, but when used in conjunction with -Wl will generate an error (as do other flags, like -v)

$ clang -mpopcnt -flat_namespace hello.c
clang: error: unsupported option '-mpopcnt' for target 'aarch64-apple-darwin'
$ clang -mpopcnt hello.c -flat_namespace
clang: error: unsupported option '-mpopcnt' for target 'aarch64-apple-darwin'
$ clang -mpopcnt -Wl,-flat_namespace hello.c
clang: error: unsupported option '-mpopcnt' for target 'aarch64-apple-darwin'
$ clang -mpopcnt hello.c -Wl,-flat_namespace
$ ./a.out
hello world

$ clang -v
clang version 19.1.3
Target: aarch64-apple-darwin24.1.0
Thread model: posix
InstalledDir: /nix/store/6b4vxqc16xq1nq8jhdsylfml244vah22-clang-19.1.3/bin

[paparodeo]

this can be reproduce on x64 linux by finding some other unsupported option: eg

$ clang -mno-mma -mhtm hello.c  
clang: error: unsupported option '-mno-mma' for target 'x86_64-unknown-linux-gnu'
clang: error: unsupported option '-mhtm' for target 'x86_64-unknown-linux-gnu'
$ clang -mno-mma -mhtm hello.c -lc
$ ./a.out
hello world

[paparodeo]

seems to be this block which is swallowing the errors:

llvm-project/clang/lib/Driver/Driver.cpp

Lines 4132 to 4139 in 47928ab

	// If we are linking, claim any options which are obviously only used for
	// compilation.
	// FIXME: Understand why the last Phase List length is used here.
	if (FinalPhase == phases::Link && LastPLSize == 1) {
	Args.ClaimAllArgs(options::OPT_CompileOnly_Group);
	Args.ClaimAllArgs(options::OPT_cl_compile_Group);
	}
	}