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Re: [PATCH] Fix DCE REG_LIBCALL note moving from noop move insns (PR rtl-optimization/33644)
On Fri, Oct 19, 2007 at 03:04:49PM +0200, Steven Bosscher wrote:
> > > Compile with -fpic. There should only be one call to __tls_get_addr
> > > to get a base address. Without libcalls there will be two calls. The
> > > base address is not exposed in tree-ssa.
> > But isn't the function marked const? (Is that the right flag?)
> __tls_get_addr is not const, and not pure either.
To expand on this:
__tls_get_addr can side effects. The only one I'm sure of offhand
is that it can allocate previously unallocated thread-local storage
for the current thread / module. I think in Alex's clever descriptor
stuff it was called indirectly through the GOT entry and could also
modify the GOT entry to call a simpler function.
But omitting those side effects is, from the POV of a conforming
program, fine. Everywhere except in the dynamic linker during TLS
setup, at least. Can't we get away with marking it const or pure?