Hello! I'm trying to dyanmically generate different bitpatterns using inline assembly depeding on a value is constant or not. I'm using it to issue system calls (see http://spel.bth.se/index.php/Cibyl) and avoid clobbering registers with constant values. What I'm trying to achieve is this: move a0,v0 # Normal MIPS instruction 0000fffd # Argument, is a constant 00000020 # Constant 32 ffff0001 # System call number 1 I use the first word as encoding of the "argument" type and the second as the constant or register number. My problem is: How can I generate this reliably from inline assembly? It seems to me that __builtin_constant_p doesn't work as I would expect it to. My syscall macros are defined as: #define _syscall1(type,name,atype,a) \ type name(atype a) \ { \ register unsigned long __v0 asm("$2"); \ \ __asm__ volatile ( \ ".set push" \ ".set noreorder " \ ".long %1" \ ".long %2" \ ".short 0xffff #" #name " " \ ".short %3" \ ".set pop" \ : "=&r" (__v0) \ :"r?i" (__builtin_constant_p(a) ? 0xfffd : 0xfffe), "r?i" (a), \ "i" (__NR_##name) \ ); \ \ return (type) __v0; \ } When I compile code which uses the above call (puts("Hello, cruel world!\n");, const char* argument), I get the following: move a0,v0 # Normal MIPS instruction 0000fffe # Argument, is a _register_ 00000020 # Constant 32 ffff0001 # System call number 1 so the funny thing here is that GCC seems to realize that the "r?i" constraint to the right can emit the constant directly (without a register), whereas __builtin_constant_p() returns false and my thought-out evil optimization fails. I realize that GCC cannot detect all constant values with __builtin_constant_p(), but in this case it seems internally inconsistent - it apparently emits a constant for the string address. Any takes? Would this qualify as a bug? My GCC is mips-linux-gcc (GCC) 3.4.4 20050314 (prerelease) (Debian 3.4.3-13) // Simon
