Invalid assembly is generated when using intel syntax

[Hubert]

Invalid assembly code is generated when intel syntax (-masm=intel) is used and there are any symbols of the same name as CPU register. For example:

int ST = 42;
int main() {
 return ST;
}

Will produce messages like:
/tmp/ccglHDgh.s: Assembler messages:
/tmp/ccglHDgh.s:21: Error: invalid use of register

The problem is that GCC will generate nonsense like that:
mov eax, DWORD PTR ST[rip]

In case of such trivial example, it is very easy to find what the problem is but it can be really tricky to find the cause in larger projects. I expect that the compiler should at least generate some clear warning that using such names can cause problems.

[Matthias Klose (doko)]

It is because ST is a register. To use -masm=intel, one should avoid
using registers, like st, rax, xmm0, .... as variables.