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Re: c/7871: ICE on legal code, global register variables problems
- From: Richard Henderson <rth at redhat dot com>
- To: Jim Wilson <wilson at tuliptree dot org>
- Cc: gcc-gnats at gcc dot gnu dot org, gcc-bugs at gcc dot gnu dot org, gcc-prs at gcc dot gnu dot org, rz at linux-m68k dot org, wilson at gcc dot gnu dot org
- Date: Thu, 27 Feb 2003 21:47:11 -0800
- Subject: Re: c/7871: ICE on legal code, global register variables problems
- References: <3E5ED649.9080002@tuliptree.org>
On Thu, Feb 27, 2003 at 10:23:53PM -0500, Jim Wilson wrote:
> ! /* Calls change all call-used registers. Calls may or may not
> ! change global registers. Since this will cause previous stores
> ! to be deleted as dead, we must assume that global registers are
> ! not set in the call. */
> for (i = 0; i < FIRST_PSEUDO_REGISTER; i++)
> ! if (TEST_HARD_REG_BIT (regs_invalidated_by_call, i)
> ! && ! global_regs[i])
I don't think this is right. The call may change the variable.
If we don't mark the value set, we won't have proper log_links.
The register was *supposed* to be marked used by
/* Calls may also reference any of the global registers,
so they are made live. */
for (i = 0; i < FIRST_PSEUDO_REGISTER; i++)
if (global_regs[i])
mark_used_reg (pbi, regno_reg_rtx[i], cond, insn);
so I'm not sure where we went wrong...
A test case that I think may fail with your change is
register int d __asm__("d7");
void bar()
{
if (d != 1)
abort();
d = 4;
}
void baz()
{
if (d != 6)
abort();
}
int main()
{
d = 1;
bar();
d |= 2;
baz();
return 0;
}
If log_links are wrong, combine will see d=1 linked with d|=2 and
produce d=3.
r~