riscv: lib: Check if output in asm goto supported

The output field of an asm goto statement is not supported by all
compilers. If it is not supported, fallback to the non-optimized code.

Signed-off-by: Charlie Jenkins <[email protected]>
Fixes: a04c192 ("riscv: Add checksum library")
Link: https://lore.kernel.org/r/20240118-csum_remove_output_operands_asm_goto-v2-1-5d1b73cf93d4@rivosinc.com
Signed-off-by: Palmer Dabbelt <[email protected]>

Author: charlie-rivos

arch/riscv/lib/csum.c

@@ -156,6 +156,7 @@ do_csum_with_alignment(const unsigned char *buff, int len)
 	end = (const unsigned long *)(buff + len);
 	csum = do_csum_common(ptr, end, data);
 
+#ifdef CC_HAS_ASM_GOTO_TIED_OUTPUT
 	/*
 	 * Zbb support saves 6 instructions, so not worth checking without
 	 * alternatives if supported
@@ -214,6 +215,7 @@ do_csum_with_alignment(const unsigned char *buff, int len)
 		return csum >> 16;
 	}
 no_zbb:
+#endif /* CC_HAS_ASM_GOTO_TIED_OUTPUT */
 #ifndef CONFIG_32BIT
 	csum += ror64(csum, 32);
 	csum >>= 32;