On Tue, Nov 24, 2015 at 8:58 AM, <paul_kon...@dell.com> wrote: > > I'm really concerned with loosening the meaning of basic asm. I > wish I could find the documentation that says, or implies, that it > is a memory clobber. And/or that it is implicitly volatile.
The volatile one is right there in the current docs. https://gcc.gnu.org/onlinedocs/gcc/Basic-Asm.html#Basic-Asm "All basic asm blocks are implicitly volatile." Even back in GCC 2.95.3, the docs say (https://gcc.gnu.org/onlinedocs/gcc-2.95.3/gcc_4.html#SEC93) "If you write an asm instruction with no outputs, GNU CC will know the instruction has side-effects and will not delete the instruction or move it outside of loops" and "An asm instruction without any operands or clobbers (and "old style" asm) will not be deleted or moved significantly, regardless, unless it is unreachable, the same wasy as if you had written a volatile keyword." However, I'm not aware that basic asm's were ever implicitly memory clobbers. Again, back in GCC 2.95.3: "If your assembler instruction modifies memory in an unpredictable fashion, add `memory' to the list of clobbered registers." Ian
