On Mon, 24 Feb 2020, Andreas Schwab wrote: > On Feb 24 2020, Petr Tesarik wrote: > > > On Mon, 24 Feb 2020 12:29:40 +0100 > > Andreas Schwab <sch...@suse.de> wrote: > > > >> On Feb 24 2020, Petr Tesarik wrote: > >> > >> > This works great ... until there's some inline asm() statement, for > >> > which gcc cannot keep track of the length attribute, so it is probably > >> > taken as zero. > >> > >> GCC computes it by counting the number of asm insns. You can use > >> ADJUST_INSN_LENGTH to adjust this as needed. > > > > Hmm, that's interesting, but does it work for inline asm() statements? > > Yes, for a suitable definition of work. > > > The argument is essentially a free-form string (with some > > substitution), and the compiler cannot know how many bytes they occupy. > > That's why ADJUST_INSN_LENGTH can adjust it.
I think Petr might be unaware of the fact that GCC counts the **number of instructions in an inline asm statement** by counting separators in the asm string. This may overcount when a separator appears in a string literal for example, but triggering under-counting is trickier. Petr, please see https://gcc.gnu.org/onlinedocs/gcc/Size-of-an-asm.html for some more discussion. Alexander
