Jeroen Demeyer <jdemeyer@xxxxxxxxxxxxx> writes: > I have a C++ program (i386 target) which has a piece of inline > assembly with the following constraints: > > asm(/* Some asm code */ > : "=&rm" (n0), "=&r" (n1), "=&r" (n2) > : "2" (n0), "1" (n1), "g" (n2), "cI" (s) > ); > > When compiled with g++ 4.1.2 (CXXFLAGS=-O2 -march=pentium4) the > operands %0 and %5 get the same memory address, even though they refer > to distinct variables (n0 and n2). So, is this a bug in g++ 4.1.2 or > am I doing something wrong? g++ 3.4.6 and g++ 4.3.1 generate correct > code, but that does not really prove anything. It would help to see the types of the variables. Is n2 a pointer? Also it would help to see the actual values that wind up getting passed in. With "=%rm" you are telling gcc that it is OK to pass a memory address. And "g" accepts any operand. That gives gcc a lot of flexibility. If it does wind up passing in a memory operand for both, though, it seems to me that they should not overlap. I think more details would help. For example, run gcc with the -dg option, look at FILENAME.xxx.greg, and show us the insn corresponding to the asm statement. > In particular I would like to know: > 1) Is it allowed to put matching (digit) constraints referring to > different variables? This is what I do with %2. The same register is > used as input for variable n0 and as output for variable n2. Yes, that is fine. > 2) Is there a way to specify some kind of 'earlyclobber' (&) modifier > with a memory constraint? How can I prevent gcc from putting an input > variable and an unrelated output variable in the same memory location? The simple way is to force one or both of them into registers. Ian
